Final Exam (Psyc 110)

 Chapter 11.5 Navigation Notes 

Reading notes:

• Such world-centered representations are sometimes called allocentric (They can also be called cognitive maps,)  to distinguish them from egocentric 

• A cognitive map can help an animal identify shortcuts and chart detours. We certainly use our own cognitive map in this manner

• place cells indeed exist in the hippocampus. discovered by John O’Keefe.  Importantly, neurons that increase their firing rate at a particular location do so regardless of the direction in which the rat is facing. By definition, such neurons encode spatial information in allocentric, rather than egocentric, coordinates.  (Most hippocampal neurons have only one specific area, or "place field," where they activate within the arena.)

• All of these findings support the notion that hippocampal place cells are part of the brain’s cognitive map. It is important to note, however, that adjacent place cells almost never encode adjacent spatial locations. Therefore, they do not really form a map;

• In this study, epilepsy patients had electrodes implanted in their hippocampus and other brain areas. They played a computer game where they drove a virtual taxi, picking up passengers and dropping them off at specific stores. One neuron’s activity in a patient’s right hippocampus is shown in (B). The red square (outlined in black) marks a spot where this neuron consistently became more active. This suggests that certain neurons respond to specific locations in the virtual town. The histogram in (C) shows that these "place-responsive" neurons are most commonly found in the hippocampus.

• In (D), researchers found that these neurons fired in the same location no matter which direction the taxi was moving. This suggests that hippocampal neurons track location based on the overall environment (allocentric coordinates) rather than the person’s own movement direction (egocentric coordinates)

• grid cells in the entorhinal cortex. 

• These neurons have multiple place fields that are arranged in a triangular grid-like pattern. Theoretical models suggest that hippocampal place cells may obtain their single, unique place fields by combining inputs from multiple grid cells with different grid spacings

Slides Notes: 

• Animals can learn the spatial layout of their environment (place learning) but overtrained animals (2 weeks of training) go “on autopilot” 

• Spatial learning refers to the ability to acquire, store, and utilize information about the spatial relationships within an environment, often involving creating a mental map, while habit learning is the automatic acquisition of a behavior through repeated exposure to a stimulus-response association

• Silencing the hippocampus during testing disrupts the place learning strategy (but not “habit learning”)

• The “Morris water maze” is often used to study spatial learning in rodents such that After being dropped into the tub at random starting locations, rodents soon learn where to find a submerged platform (where they can rest)

• Hippocampus lesions impair spatial learning in the Morris water maze: If the platform is raised out of the water (visible), then the animals swim to it quickly, indicating that they have no motor or motivational impairments but rather lose of spatial learning 

• “Place cells” in the rat hippocampus fire selectively in a specific location : They do so regardless of the rat’s orientation, Neighboring neurons may have very different place fields

• “Place cells” can also be recorded in humans navigating a virtual environment: 

• A place cell is a type of pyramidal neuron within the hippocampus that becomes active when an animal enters a particular place in its environment; this place is known as the place field. A given place cell will have only one, or a few, place fields in a typical small laboratory environment, but more in a larger region.

• A grid cell is a type of neuron in the brains of many species that allows them to understand their position in space. A grid cell was first described in the entorhinal cortex. Grid cells derive their name from the fact that connecting the centers of their firing fields gives a triangular grid

• Tolman cross maze & Morris water maze have both been used to demonstrate that rats are capable of allocentric navigation. Such that overtrained animals tend to navigate along habitual routes ignoring their cognitive map 

Chapter 14 Memory Notes 

14.1. How many forms of learning and memory are there?

>Episodic memory: Specific memory that is specific to an individual (ex: Remembering where you parked your car this morning)  

>Semantic memory: the ability to recall general knowledge, facts, or concepts. (ex:Knowing who won the Civil War, knowing that football is a sport) 

>Declarative/Explicit Memory: the ability to consciously recall facts, events and concepts of  effort (ex:Remembering the birth dates of friends) 

>Non-declarative (implicit memory): a type of memory that's unconscious and doesn't require conscious effort to retrieve (ex:Learning to associate a specific sound with a particular event, riding a bike) 

>Classical conditioning (pavlovian conditioning/associative learning): Classical conditioning is when a neutral stimulus gets associated with a naturally-occurring stimulus causing the neutral stimulus to eventually trigger a response (pavlov ex: dogs being conditioned to salivate after they hear the bell, before food stimulus is presented)

>Pavlov’s dogs learned to salivate in anticipation of food → This form of “procedural learning” (the process of acquiring skills and habits that can be performed automatically, long term, Procedural memory/implicit memory)

• In a typical experiment, a specific sound was repeatedly presented just before the food. After several trials, the dog learned to salivate in response to the sound, even when no food was present. 

>A very small number of people have highly superior autobiographical memory

• Researchers wanted to find people with superior autobiographical memory (the ability to remember personal events in great detail). To do this, they tested people who claimed to have this ability by asking them 30 questions about public event

• Interestingly, even though these individuals are great at remembering personal events, they are often average at other types of memory tasks—such as remembering lists of numbers or doing well in school.

>People who are terrible at remembering a tune are unlikely to become musicians (though they might get better with training), suggests that learning a second language at an early age makes it much easier to learn additional languages later

 14.2. What’s wrong with H.M.?

>Anterograde amnesia: Inability to form new memories, still able to recall events from prior to the event/trauma 

>Retrograde amnesia: Inability to recall old memories (prior to event), still able to form new memories

>Medial Temporal Lobe: includes hippocampus, amygdala, and parahippocampal regions

>Patient H.M.

• Patient H.M. had his amygdala, hippocampus, and parts of the adjacent cortices surgically removed bilaterally (to treat intractable epilepsy) 

• Patient H.M. (Henry Molaison) remained able to learn new skills including both motor and cognitive skills

• In the rotary pursuit task, a person has to keep a pointer on a moving target that goes around in a circle. The control group got better at this task quickly with practice. H.M also got better at it after practicing. However, after about four practice sessions, he stopped improving.

• The interesting part is that even though H.M. got better at the task, he never remembered doing it before. This shows that his ability to learn movements (motor skills) was still working, even though his memory for events was damaged (Anterograde amnesia) ; form new memories  .

• HM suffered epileptic seizures. Surgery in 1953 at age of 27. The surgery was successful in alleviating seizures. H.M. surgery: bilaterally removed including cortex, the amygdala, the anterior two-thirds of the hippocampus.

• Brenda Miller,Psychologists who studied H.M. discovered the role of medial temporal lobe in human memory. Such surgery had no effect on perception, intelligence or personality, but Strong deficit in anterograde amnesia. Normal working memory. He will remember a number for a short time but when distracted he will not only forget the number but also that the event occurred. (Lost ability to form new episodic memories)

>Memory consolidation depends on the integrity of the temporal lobe. Brain injuries can cause amnesia, which means memory loss. There are two main types:

•  Retrograde amnesia – A person forgets events that happened before the injury, but they can still remember older memories and new events after the trauma.

• Anterograde amnesia – A person remembers everything before the injury, but they cannot form new memories after the trauma.

>Patient E.P

• E.P. patient developed memory impairment following an episode of herpes simplex encephalitis ( viral infection there was damage to the hippocampus)

• large bilateral lesions of the medial temporal lobe (where the hippocampus lies) 

• severe anterograde amnesia (tested on verbal on nonverbal recognition memory

• partial (graded) retrograde amnesia

• memory-related abilities may be impaired, other abilities, such as movement, perception, or problem-solving, are still intact

• Structures in the medial temporal lobe (hippocampus) involved in declarative memory formation

>H.M & E.P symptoms are similar but H.M had surgery for epilepsy & E.P damage to hippocampus due to viral infection 

 14.3. Can H.M.’s amnesia be reproduced in non-humans?

> Studies on monkeys and rats show that a brain area called the perirhinal/postrhinal cortex is important for recognizing objects. However, the hippocampus is not necessary for this. Instead, the hippocampus helps remember relationships between things, like locations or connections between different pieces of information.

>To replicate H.M’s form of amnesia, scientists used object recognition tasks 

• In the delayed non-match to sample task, animals are shown an object and then, after a short delay, given a choice between the same object and a new one. To get a reward (like food), they must pick the new object. Monkeys can learn this rule with practice.

• For rodents, researchers use the spontaneous object recognition task, which takes advantage of their natural curiosity

>Hippocampus lesions also impair the memory for temporal relationships (sequences)

• Rats were trained to dig in cups of scented sand to find a reward. First, they were exposed to a series of different smells in a specific order.

• To test their memory of the sequence, they were later given two cups with different smells and had to choose the one they smelled earlier in the sequence to get a reward.

• If the rats had damage to both sides of their hippocampus, they struggled with this sequence memory test.

•  However, In contrast, hippocampus lesions do not impair performance on a simple odor recognition test in which rats are trained to select a novel odor

>amygdala (a part of the brain involved in emotions) wasn't the main cause of HM's memory problems. However, they didn't fully realize how important the brain areas next to the hippocampus (called the entorhinal, perirhinal, and parahippocampal cortices) were. These areas were also damaged in HM, and this damage played a role in his memory issues. (they are input and output pathways for hippocampus, plays a role in memory and spatial navigation)

>Entorhinal cortex: Helps connect information from different parts of the brain to the hippocampus, which is important for forming new memories.

>Perirhinal cortex: Involved in recognizing objects and their features.

>Parahippocampal cortex: Helps with recognizing places and spatial memory (remembering where things are).

14.4. How are hippocampus-dependent memories created, and how are they recalled?

>Role of hippocampus: crucial for forming new explicit memories; case proved how crucial hippocampus is to memory formation

>The hippocampus is connected to the entorhinal cortex, which is connected to the perirhinal/postrhinal cortex. These areas are all linked to many other parts of the brain neocortical areas

>In the hippocampus, area CA3 acts like a network that helps link memories by connecting cells in a pattern (called Hebbian cell assemblies). This pattern can create memory traces.

>The idea is that when the hippocampus "reactivates" a group of connected cells (a cell assembly), it can recreate the same activity pattern in the brain that happened during the original experience, helping you recall a memory.

>Information flows from neocortex into the hippocampus, and back

• The hippocampus includes the dentate gyrus, CA3, CA1, and the subiculum

• 1) Entorhinal Cortex→ ( Perforant Pathway) → 2) Dentate Gyrus → (Mossy Fiber Pathway) → 3) CA3 → (Recurrent Collaterals) → 4) CA1

• Information generally flows from higher order neocortical areas through the perirhinal/postrhinal and entorhinal cortices into the hippocampus and back out.

• Hippocampal CA3 neurons receive input through three major pathways ( From entorhinal cortex; From the dentate;  From other CA3 neurons)

• The projection from the entorhinal cortex to neurons in the dentate gyrus and CA3 is called the perforant path because it “perforates” the boundary between the dentate and the entorhinal cortex.

• The mossy fiber pathway connects the dentate gyrus to CA3. the neurons of CA3 project to CA1 and, via recurrent collaterals, to other CA3 neurons.

>LTP in the CA3-CA3 pathway is Hebbian

• electrode to record activity from individual neurons in the CA3 area of the hippocampus. They applied electrical stimuli to the axons (the long parts of neurons that carry signals) of other neurons in the same area.

• When they used strong, high-frequency stimulation (called tetanic stimulation), it made the synapses (connections between neurons) stronger, and this effect lasted for at least an hour. This is called long-term potentiation (LTP). Specifically, the synapse's response (EPSP) became bigger and faster after the stimulation.

• The graph shows that weak stimulation alone doesn't cause LTP. However, when combined with a strong electrical charge inside the receiving neuron (called depolarization), LTP occurs. This follows Hebb's rule, which says that when two neurons are active at the same time, their connection becomes stronger.

>Memory recall-related firing of a neuron in the human entorhinal cortex

• electrodes were placed in the hippocampus and entorhinal cortex of patients who were waiting for epilepsy surgery. They recorded the activity of a neuron in the entorhinal cortex while the patient watched short 5-second clips from The Simpsons.

• The neurons become more active when the patient watches those clips. Later, when the patient was asked to remember which clips they had seen, the same neuron fired again right before the patient recalled watching The Simpsons.

• This shows that certain neurons become active when people remember something. Similar patterns of activity have also been seen in the hippocampus, which is important for memory.

>Memory recall activates a subset of the cortical regions activated during perception

• People were asked to memorize 20 pictures and 20 sounds. Functional MRI was performed as they viewed the pictures, listened to the sounds, or tried to recall those stimuli as vividly as possible. 

• Recalling pictures activated a subset of the same brain regions that were activated during perception of the pictures (occipital lobe) 

• Recalling sounds activated a subset of the regions activated during listening (temporal lobe)

>a widely accepted model, memory formation involves the formation of hippocampal cell assemblies

• memory recall involves the “reinstatement” of neocortical activity

• memories are created when a group of neurons in the neocortex (part of the brain involved in higher functions) becomes active at the same time. This activity helps form a corresponding group of connected neurons, called a cell assembly, in the hippocampus, which is important for memory.

• During recall (when you remember something), activating just a few of those original neocortical neurons can trigger the hippocampal cell assembly. This then "reinstates" the brain activity that was happening during the original experience, helping you remember what happened.

>Brain exercise 

• The main challenge is that it's tough to measure memory recall and record from both the hippocampus and neocortex at the same time.

14.5 – What happens to memories as they grow old ?

>The standard model of systems consolidation suggests that when memories are repeatedly reactivated in the hippocampus, they help form permanent memory groups (called cell assemblies) in the neocortex. Over time, these groups can be activated on their own, without needing the hippocampus anymore.

>Hippocampus lesions impair recent memories much more than distant (old) memories

• resulting in a “retrograde amnesia gradient”

• Humans with bilateral damage to the hippocampus have impaired memory for major news events that happened after their injury (anterograde amnesia) or 1–5 years before the brain damage (retrograde amnesia); older memories are not impaired 

• Similarly Monkeys learned 100 different 2-choice object discrimination problems (only one member of each pair was rewarded) at various intervals prior to brain surgery. Hippocampus lesions weakened only the 2- and 4-week old memories but not older memories 

>Repeated reactivation of cortical neurons generates cortical cell assemblies

• A standard model of memory consolidation, repeated reactivation of the neocortical neurons is thought to strengthen the connections between them, leading to the formation of a neocortical cell assembly that can then be activated without involving the hippocampus.

• This is often called “systems consolidation”

>Brain exercise: Synaptic consolidation is when changes in the strength of connections between neurons (synapses) are stabilized. Systems consolidation is when memories in the neocortex gradually become stronger and can eventually be recalled without the hippocampus. Most scientists believe that strengthening synapses is key to long-term memory, but other possibilities, like DNA changes, might also play a role.

 14.7. How do animals learn what’s dangerous?

>Animals have a variety of rapid and robust mechanisms for learning what is dangerous

>In auditory fear conditioning, rats learn to freeze in response to a tone previously paired with an aversive stimulus. The underlying neural circuits run through the basolateral and central nuclei of the amygdala.

>In contextual fear conditioning, animals learn to fear environments in which bad things happen to them. Recalling recent, but not old, contextual fear memories requires an intact hippocampus

>It usually takes just one trial for a rat to avoid a place where it was scared. The ability to express inhibitory avoidance is hippocampus dependent for a few weeks but then becomes hippocampus independent.

>Inactivating the amygdala interferes with auditory fear conditioning

• In auditory fear conditioning, rats are tested in a new chamber to make sure they fear the tone, not just the chamber. 

• If you use a drug called muscimol (GABA antagonist) to inactivate certain parts of the amygdala (the central nucleus or basolateral complex) during training or testing, 

• the rats freeze less in response to the tone. This shows that these parts of the amygdala are important for fear learning and memory.

>Contextual fear conditioning involves both the amygdala and the hippocampus

• In contextual fear conditioning, a rat is tested to see if it remembers the chamber where it got a footshock. If the rat freezes in that chamber, it shows it remembers the context (the chamber) and associates it with fear.

• If you inactivate the basolateral amygdala (BLA) with a drug called muscimol, either during training or testing, the rat’s freezing response (fear) is weaker, meaning it has trouble remembering the chamber and the shock.

• If the hippocampus is damaged within 14 days after training, it also impairs the rat's ability to remember the context and show fear. However, auditory fear conditioning (fear learned from a sound) is not affected by these hippocampal lesions.

> More Key terms:

> hippocampus: is a part of the brain that helps with learning, memory, and spatial awareness

>CA1: a subfield of the hippocampus, a brain structure crucial for memory (episodic)  and spatial navigation. Forms the first layer of the hippocampal circuit, consisting of pyramidal neurons arranged in a dense layer.

> CA3: encoding and storing new memories, particularly episodic memories (personal experiences). It is thought to create a network of neurons that represent the specific event or experience. & Pattern separation such us it helps distinguish between similar memes, preventing confusion and ensuring accurate retrievals 

>Dentate gyrus: in the medial temporal lobe, on the inner surface of the hippocampus, It receives information from the entorhinal cortex and processes it to create new memories. Spatial navigation: It helps in forming a map of the environment and remembering location

>subiculum: a part of the hippocampus that acts as an output structure for the hippocampal formation

>entorhinal cortex: an area of the brain's allocortex, located in the medial temporal lobe, whose functions include being a widespread network hub for memory, navigation, and the perception of time

>perirhinal cortex: a region located within the temporal lobe that plays a crucial role in various types of learning, including recognition memory and familiarity discrimination (Involved in recognizing objects and their features) 

>Amygdala: processing emotions, especially fear

>model of memory in CA3 (recurrent collateral input):  crucial for memory storage due to its strong internal connections. These allow for pattern completion, meaning even a small memory fragment (autoassociative) can reactivate the full memory. This happens through attractor dynamics, where partial input spreads activation across the network, reconstructing the entire memory. If you recall just a small part of an experience, the CA3 region helps activate the rest of the memory.

>memory (encoding, cued recall): Encoding is how information is stored in memory, and cued recall is a way to retrieve that information with the help of cues

>Cue vs recall: A "memory cue" is a hint or prompt that helps trigger the retrieval of a specific memory, while "memory recall" is the act of actively retrieving information from memory, which can be done with or without the assistance of a cue

>Model of memory formation hippocampal assembly: new memories are encoded by the coordinated firing of groups of neurons in the hippocampus, forming distinct "cell assemblies" that represent specific experiences; Stronger connections within these assemblies make memories easier to recall later.

>memory recall (reactivation): the process of reactivating a memory through a cue or recall. It's a key part of memory that helps strengthen existing memories and incorporate new information. Reactivation can occur during sleep or wakefulness. It can involve re-expressing neural activity patterns that were present when the memory was first formed.

>memory recall (pattern completions): can retrieve a complete memory based on only a partial or incomplete cue, essentially "filling in the gaps" to reconstruct the whole experience, often facilitated by the hippocampus in the brain. Cells that have “wired together” in a cell assembly can spread an input from a subset of neurons to the entire assembly.

>role of cortex memory: processing and interpreting sensory information, facilitating the formation, storage, and retrieval of memories

>memory consolidation (hippocampus & neocortex)( a systems consolidation): the process where newly formed memories, initially dependent on the hippocampus, gradually become more independent and stored primarily within the neocortex over time, a phenomenon known as "systems consolidation.

>replay of activity patterned during sleep :  where the brain during sleep reactivates neural patterns that were previously active during waking experiences, essentially "replaying" memories or learned behaviors, which is believed to be a crucial part of memory consolidation and learning process, primarily occurring in the hippocampus region of the brain.

>enhancement of memory encoding & recall: strategies like deep processing by relating new information to existing knowledge, creating vivid mental images, actively engaging with the material through self-generation, chunking information, practicing retrieval through quizzes, and considering the context and emotional state during learning; essentially, the more actively and meaningfully you process information, the better it will be encoded and remembered later on

>amygdala & memory consolidation: The amygdala is involved in memory consolidation by regulating the activity of other brain regions. The amygdala is especially involved in consolidating memories that are emotionally arousing (involved in effectively influenced memory)

>Fear memory (hippocampus, amygdala, cortex): the amygdala (primarily responsible for processing fear), the hippocampus (encoding contextual details of a fear-inducing experience), and the prefrontal cortex (regulating and potentially inhibiting fear responses), with the amygdala considered the central hub for fear memory formation and retrieval

>Practice Questions: 

1)Someone who has anterograde amnesia would have an inability to remember which of the following?

a) their mother’s name

b) how they drove to work that day

c) the location of the home they grew up in

d) all of the above

2)Which of the following were important discoveries regarding learning and memory that patient H.M. contributed to?

a) neuronal activity in the medial temporal lobes is necessary for recalling long-term memories

b) neuronal activity in the medial temporal lobes is necessary for procedural learning

c) neuronal activity in the medial temporal lobes is necessary for the formation of new episodic

memories

d) neuronal activity in the medial temporal lobes is necessary for performing cognitive tasks

3)The hippocampus is necessary for ___relational memory__, connecting memories of objects through space and time.

4)Many CA3 neurons project to a dense network of additional neurons creating an autoassociative_network of recurrent connectivity.

5)Cells that have “wired together” in a cell assembly can spread an input from a subset of neurons to the entire assembly. This process is called_____________.

a) long term potentiation

b) pattern completion

c) Hebbian synapse

d) sequence learning

6)Memory consolidation requires relocation to the neocortex, which is termed ___Systems___ consolidation.

7)In rat experiments, it has been shown that the conditioned fear response is mediated predominantly by the ___________, while the contextual fear response also involves the ______________ .

a) neocortex, amydala

b) hippocampus, amydala

c) amydala, hippocampus

d) thalamus, hippocampus

Chapter 13 Brain States  

13.1. How does the brain generate and direct attention?

>Attention generally improves performance on perceptual (or motor) tasks. It differs from behavioral arousal in being selective to particular stimuli, stimulus features, or regions of space.

>Visual spatial attention can be voluntary, such as when you are searching for a specific object in a cluttered space, or “grabbed” against your will by salient stimuli. Although spatial attention is often accompanied by orienting movements, it can also be covert.

>Salient stimuli may activate neurons in the superior colliculus, which then direct attention toward the stimulus. With strong stimulation, the shift in attention is accompanied by orienting movements to the stimulus location; with weak stimulation, the shift is covert.

>Voluntary spatial attention, you choose to focus on a specific area in your vision. The frontal eye fields (FEF), a part of your brain, help control this focus. When you pay attention to a certain spot, the neurons that process information from that area become more active—but only when they see something they are naturally tuned to respond to (their "preferred stimuli"). If something unimportant appears in that area, these neurons don’t react as strongly.

>How rapidly does the red circle “pop out” ?

• Voluntary attention: refers to the conscious and deliberate act of focusing on a specific stimulus or task, while (reading a book while ignoring the background noise)

• involuntary attention is when attention is automatically captured by a salient stimulus without conscious effort, (like a loud noise or bright light)

• See a red circle among only blue circles, it stands out instantly, no matter how many blue circles there are. Your brain processes everything at once—this is parallel search, which happens automatically.

•  But if the red circle is mixed with both blue circles and red stars, it takes longer to find because you have to check each shape one by one—this is serial search, which is slower and requires effort.

• Parallel search: several stimuli are attended at the same time with no decrease in efficiency.(automatically, involuntary)

•  Serial search: only one stimulus is attended at a time. (goal directed/voluntary)

>Even “covert attention” improves perception

• Helmoltz discovered that he could read the letters wherever he focused his attention Because his eye remained fixated on the yellow spot, Helmholtz used “covert attention

• Helmholtz tested attention by looking at letters in a dark box. When a flash lit up the letters, he couldn’t read any because his focus was on a single light spot. But when he mentally chose to focus (attention) on a specific area before the flash, he could read the letters there—without moving his eyes. This showed that attention can shift covertly (without eye movement).

• Covert attention: paying attention without moving the eyes. 

• Overt attention: selectively processing one location over others by moving the eyes to point at that location (Looking both ways before crossing the street)

• Frontal eye field (EFE) activity correlates with covert voluntary attention

>People rarely use covert attention (shifting focus without moving their eyes) on purpose, but it happens naturally. Before you move your eyes or head, your attention shifts first.

>The “saliency map” model of spatial attention predicts real attention well

• Your brain quickly scans a scene to detect in parallel to see differences in color, brightness, and shape, and feature . It combines this info into a saliency map, highlighting the most eye-catching spots. 

• Your attention goes to the most important area first, but the brain lowers its importance after a moment (inhibition of return) to help you focus on new things.

• Salience is the property by which something stands out, noticeable 

>The superior colliculus is a critical player in the neural circuits underlying attention

• So is the pulvinar nucleus (of the thalamus), which conveys attention related signals to the visual cortices

• brain pathways that control eye movements and visual attention. Information moves from the superior colliculus through the pulvinar nucleus, V1 (primary visual cortex), and higher visual cortices . 

• The frontal eye field (FEF) helps guide voluntary attention, while other pathways process vision and movement.

• LGN = lateral geniculate nucleus.

>Brain exercise: Why is it important that weak stimulation of neurons in the superior colliculus improves movement perception only in a specific region of space (rather than everywhere)?

• If weak stimulation of neurons in the superior colliculus improved perception everywhere, it would suggest the brain is just getting more alert (increased arousal), not focusing on a specific area. Attention is selective, meaning it should enhance perception only in a targeted region, not across the whole visual field.

>Hemispatial neglect is characterized by inattention to the left side of objects or the world

• It is generally caused by lesion of inferior parietal and/or superior temporal cortex on the right side of the brain

• Patients with hemispatial neglect often ignore the left side of things when asked to copy simple drawings, like a flower or clock, and only copy the right side. 

• This issue is mainly related to attention, not perception or movement. 

• Brain scans show that the damage typically happens in the right side of the brain, especially in areas where the parietal and temporal lobes meet. The more overlap in these areas, the more severe the neglect.

>Brain exercise: What would happen to your perceptual abilities if attention were to increase the responses of cortical neurons to all stimuli, not just those that the neurons already prefer?

• it would create a lot of confusion. Imagine a room where everyone talks louder at once—it would become harder to focus on any one person. Similarly, in the brain, attention works best when it boosts responses only to preferred stimuli, making the important signals clearer while reducing unnecessary "noise."

13.2. What mechanisms generate behavioral arousal?

>Wakefulness and behavioral arousal are associated with EEf desynchronization (smaller, more irregular EEG traces)

>Electrical stimulation in the reticular formation can trigger arousal. This effect probably results from the activation of noradrenergic axons from locus coeruleus and cholinergic axons from peribrachial neurons.

>The locus coeruleus is a small area in the brain that has a few neurons, but these neurons send signals all over the brain. They use a chemical called norepinephrine to communicate. These neurons get activated by things that are exciting or attention-grabbing.

>Most neurons become more responsive to stimuli and reduce their background firing rate in response to noradrenergic stimulation. The prefrontal cortex is unusual in that its neurons are inhibited by high levels of norepinephrine.

>The electroencephalogram (EEG) reflects behavioral states

• Synchronized EEG: Large amplitude, low frequency waves

• Desynchronized EEG: smaller amplitude, more irregular EEG traces

• As people become drowsy and then fall asleep, their EEG becomes dominated by large-amplitude slow oscillations (synchronized) (waves).

• These slow waves disappear during rapid eye movement (REM) sleep

>Locus Coeruleus

• Its neurons project widely throughout the central nervous system and release norepinephrine (Fight-or-flight response, alertness, attention, and cognitive function, Mood regulation, sleep-wake cycle, promoting arousal and wakefulness.)

• regulate states of attention and vigilance as well as activity of the sympathetic nervous system.

• The LC is active during wakefulness and less active during sleep. It helps to transition between sleep and wake states

• located near that fourth ventral, that are important for the arousal system include the cerebellum, thalamus, neocortex, and brainstem

13.3. Why do we sleep, and what helps us wake up?

>Sleep is good; its rest your body and brain, although the brain is not shut off entirely. After all, you can be roused from sleep by your own internal rhythm and by highly salient stimuli.

>Sleep is divisible into slow-wave and rapid eye movement (REM) sleep. During REM sleep, the EEG is as desynchronized as it is during the waking state, but muscle tone is minimal. 

>The rhythmic activation of cortical neurons during slow-wave sleep results from intrinsic neuronal rhythms as well as looping interactions between the neocortex, the dorsal thalamus, and the thalamic reticular nucleus.

>Waking from sleep involves the activation of basal forebrain cholinergic neurons, which receive input from glutamatergic peribrachial neurons, locus coeruleus, and hypocretin neurons in the hypothalamus. Loss of the hypocretin neurons causes narcolepsy

>A small group of neurons in the ventrolateral preoptic area is more active during sleep than during waking. These neurons inhibit wakefulness promoting neurons and are, in turn, inhibited by them

>Neural and Motor Correlates of Sleep

• A sleeping rat spends most of its time in slow-wave sleep, with brief periods of REM sleep and occasional wakefulness.

•  During slow-wave sleep, the brain shows large, slow electrical waves because groups of neurons in the cortex fire together. 

• Muscle tone is low in both slow-wave and REM sleep, which is measured using EMG electrodes. The regular spikes in the EMG are from the heartbeat, which keeps beating during REM sleep.

>Looping connections can generate rhythmic oscillations

• The red connection is inhibitory; the others are excitatory

• Rhythmic oscillations result if the thalamocortical neurons exhibit post-inhibitory rebound firing

• Neurons in the thalamic reticular nucleus send inhibitory signals (red) to neurons in the dorsal thalamus, which then send excitatory signals (black) to the neocortex and back to the thalamic reticular nucleus. 

• The neurons in the neocortex are excitatory and send signals back to both the dorsal thalamus and the thalamic reticular nucleus. 

• This setup, along with some natural delays and the rebound effect after inhibition, allows the system to create rhythmic activity in the brain.

13.4. What’s happening during REM sleep?

>The EEG desynchronization during REM sleep is caused primarily by the basal forebrain cholinergic neurons, which are quiet during slow-wave sleep but tend to increase their firing rate during REM sleep. 

>In contrast, the locus coeruleus and tuberomammillary neurons remain silent during REM.

>When people are suddenly woken from REM sleep, they generally report having had vivid dreams (less vivid dreams occur also in slow-wave sleep). Because vivid dreams and rapid eye movements occur at the same time, it is reasonable to suppose that dreamers move their eyes to scan the dream environment

>During REM sleep, most of the body’s muscles are paralyzed, except for the heart, smooth muscles, diaphragm, and eye muscles. 

>Muscle atonia The skeletal muscles lose their tone because the motor neurons controlling them are hyperpolarized, meaning they’re less active during REM sleep.

>REM sleep might start in two ways. One idea is that glutamatergic neurons in the peribrachial region activate cholinergic neurons in the basal forebrain. 

>Another idea is that during REM, neurons in the ventrolateral periaqueductal gray (vl-PAG) stop firing, which turns on neurons in the peribrachial and subcoeruleus regions. These regions influence each other in a way that may act like a toggle switch, deciding whether the animal is in REM or slow-wave sleep.

>more key terms 

>superior colliculus, : in midbrain it is  important for visual and sensorimotor integration such as eye and head movement, spatial navigation, sensory integrations 

>parietal eye field (PEF) : involved in reflexive saccade triggering (rapid involuntary eye movement) and visual attention

>Frontal eye field (FEF): primarily involved in planning and executing saccadic (rapid, jerky) eye movements and plays a role in voluntary control and spatial attention (convert)

>Arousal: a state of being alert and responsive, or waking from sleep

>sleep: a natural, recurring state of rest that involves reduced physical activity and altered consciousness

>Slow-wave Sleep : a deep stage of non-rapid eye movement (NREM) sleep characterized by slow, high-amplitude brain waves called delta wave

>REM Sleep : a distinct sleep stage characterized by rapid eye movements, increased brain activity, and vivid dreaming

>Thalamus: relay station for input information, It also plays a key role in sleep, wakefulness, consciousness, learning, and memory.

> rhythmic oscillations: The thalamus and cerebral cortex are interconnected, forming a complex network that generates diverse oscillatory rhythms, often detectable by scalp EEG. These oscillations, ranging from slow (delta, theta) to fast (alpha, beta, gamma), are fundamental to brain function

> thalamocortical neurons:  including those in the reticular nucleus, contributing to these oscillations, which are essential for various brain functions, including sleep, attention, and seizure

>protective thick layers surrounding the brain and spinal cord, consisting of the dura mater (outermost),

>arachnoid mater (middle) spiderweb like 

> pia mater (innermost)

>subarachnoid space (between the arachnoid and pia mater) containing cerebrospinal fluid

>EEG (electroencephalogram) brainwaves are classified by frequency (in Hertz or Hz)

•  with alpha (8-12 Hz) associated with relaxed wakefulness,

• beta (13-30 Hz) with alert/active thinking

• delta (0.5-4 Hz) with deep sleep and certain abnormal state

>practice questions

1)Which of the following is an example of covert spatial attention?

a) Turning your head when you hear a loud crash

b) Being startled awake by a loud thunk in your house

c) Keeping your head facing forward while driving but still paying attention to the conversation you have with a passenger in the car

d) Diverting your attention back and forth form a powerpoint slide to the lecturer giving the presentation

2)What sort of search are you performing when you identify the green heart in the image above? (image is a bunch of red hearts, one green heart, and a lot of green triangles)

a) serial search

b) parallel search

c) salient search

d) all of the above

3)The amplitude of an EEG of a drowsy individual is _________(than) an individual that is behaviorally aroused.

a) the same as

b) higher

c) lower

d) slower

e) faster

4)Projections from the__ locus coeruleus _____, located near that fourth ventral, that are important for the arousal system include the cerebellum, thalamus, neocortex, and brainstem.

5)The feeling of “sleep paralysis” is caused by caused by the hyperpolarization of skeletal muscle neurons in a state called_____muscle atonia______.

6)Why do we not physically act out our dreams during REM sleep?

your brain sends signals to relax muscles essential for body posture and limb movements, preventing you from acting out your dreams. This temporary paralysis is called atonia

7)Explain in your own words the short and long-term effects of repeated, prolonged sleep deprivation.

in the short term, leads to impaired cognition, reduced alertness, and increased irritability, while long-term can lead to serious health problems like heart disease, diabetes, and mental health issues.

Chapter 16 Selecting Actions, Pursuing Goals

 15.1. What is the frontostriatal system?

15.2. What are the direct and indirect pathways through the striatum?

 15.3. What is the influence of dopamine on the frontostriatal loops?

15.4 – How do we learn what to do when ?

15.5. How do the dorsal and ventral striatum relate to one another?

15.6. What to do with the prefrontal cortex?