NEURO CHPT 14

Dyslexia

Impairment in learning to read write; most common learning disability

Slow word recognition

All orthographies

Inaccurate mapping of phonemes to graphemes:

Deep orthographies

cortical networks and dyslexia

Reduced activity in the left temporoparietal, occipitotemporal, and inferior frontal cortex, Reduced gray matter volume, temporal abnormalities, Reduced functional connectivity between the medial geniculate nucleus and auditory cortex

Eric Kandel and his coworkers (2015)

Measured neurotransmitter output from a sensory neuron, Verified that less neurotransmitter is released from a habituated neuron than from a nonhabituated one

neural basis of habituation

change in presynaptic calcium channels (reduced sensitivity of calcium channels), leading to a decrease in neurotransmitter

Sensitization

enhanced response to some stimulus, occurs within particular context

Associative learning

Entails an enduring neural change in a postsynaptic cell after an EPSP from the presynaptic cell crosses the synaptic gap

Long-term potentiation (LTP)

involves persistent strengthening of synapse based on recent activity patterns; produces a long-lasting increase in signal transmission between two neurons

in response to stimulation at a synapse, LTP..

changes amplitude of an excitatory postsynaptic potential lasts for hours to days or longer

Long-term depression (LTD)

Low-frequency stimulation produced a decrease in EPSP size, clears out old memories

Glutamate acts on two types of receptors on the postsynaptic membrane:

AMPA, NMDA

AMPA

responds to glutamate

NMDA

doubly gated channels, Normally blocked by magnesium (Mg2+) ions

Two events that occur together or rapidly for NMDA receptors to open:

1) Depolarization of postsynaptic membrane, which displaces Mg2+ from pore (strong electrical stimulus) 2) Activation by glutamate from the presynaptic neuron (weak electrical stimulation)

experience could change the brain in either of two ways

modifying existing circuitry or creating novel circuitry

Predominant view before the mid-1990s

The mammalian brain does not make new neurons in adulthood

BrdU technique

find newly divided cell through thyomine

Fem--Lei Chang and William Greenough (1982) Exp:

Placed patches over one eye of each rat so that the contralateral hemisphere was deprived of visual input; trained rats on a maze

Fem--Lei Chang and William Greenough (1982) conclusion:

Visual cortex of the trained hemisphere (the one that received input from the eye without the patch) had more extensive dendrites

Randy Nudo and his colleagues (1997) conclusion

Learning new motor skills, rather than simply repetitive motor use, shapes the functional topography of the motor cortex

Jon Kaas (2000)

Showed that when the sensory nerves in one limb are severed in monkeys; the relevant part of the cortex no longer responds to limb stimulation

Ramachandran (1993)

Indirectly measured the cortical maps in individuals with limb amputations

As the normal somatosensory homunculus, the __=is disproportionately large.

thumb

Arnold Scheibel and colleagues (1993)

Relationship between dendrite size in Wernicke’s area

cell complexity is related to the

computational demands required of the cel

Neurons representing the body’s trunk area have relatively __ computational demands than cells representing the finger region

less

Fear conditioning is associated with

rapid methylation, but if methylation was blocked, there was no memory

Estrogen level drops produces

increased numbers of spines on pyramidal cells in neocortex, decreased spine density in hippocampus

Menopausal women have a decline in

verbal memory ability

Middle-aged men have a

drop in spatial ability

Glucocorticoids

Released from the adrenal cortex in times of stress

Nerve growth factor

Neurotrophic factor stimulates neurons to grow dendrites and synapses and, in some cases, promotes the survival of neurons

Brain-derived neurotrophic factor (BDNF)

May enhance plastic changes, such as the growth of dendrites and synapses

Behavioral sensitization

Escalating behavioral response to the repeated administration of a psychomotor stimulant

Endogenous stem cells can be recruited to enhance functional improvement by using _______

epidermal growth factor

engram

A mental representation of a previous experience, Corresponds to a physical change in the brain, most likely involving synapses

Pavlovian conditioning

Learning procedure whereby a neutral stimulus such as a tone (CS) comes to elicit a response (CR) because of its repeated pairing with some event such as the delivery of food (UCS); also called classical conditioning or respondent conditioning

Conditioned stimulus (CS)

In Pavlovian conditioning, an originally neutral stimulus that triggers a conditioned response (CR) after association with an unconditioned stimulus

Unconditioned stimulus (UCS)

A stimulus that unconditionally—naturally and automatically—triggers an unconditioned response (UCR)

Unconditioned response (UCR)

In classical conditioning, the unlearned, naturally occurring response to the unconditioned stimulus, such as salivation when food is in the mouth

Conditioned response (CR)

In Pavlovian conditioning, the learned response to a formerly neutral conditioned stimulus

Fear conditioning

Unpleasant but harmless stimulus is used to elicit an emotional response: fear, results in learned association

Eyeblink Conditioning

experimental technique in which subjects learn to pair formally neutral stimulus with a defensive blinking response

Operant Conditioning (Instrumental Conditioning)

Learning procedure in which the consequences (such as obtaining a reward) of a particular behavior (such as pressing a bar) increase or decrease the probability of the behavior occurring again (Edward Thorndike, 1898)

Thorndike’s Puzzle Box

A cat gradually learned that its actions had consequences

Implicit memory (unconscious)

Subjects demonstrate knowledge, such as a skill, conditioned response, or recalling events on prompting, but cannot explicitly retrieve the information

Explicit memory (conscious)

Subjects can retrieve an item and indicate that they know they retrieved the correct item.

Priming

Using a stimulus to sensitize the nervous system to a later presentation of the same or a similar stimulus; unconscious learning

Gollin Figure Test

On a retention test, participants identify the image sooner, indicating some form of memory for the image

how do amnesic subjects perform on the Gollin Figure Test

show improvement even though they do not recall having taken it.

Pursuit-Rotor Task

People with amnesia, a partial or total loss of memory, perform implicit memory tests at normal.

Declarative memory (explicit)

Ability to recount what one knows, to detail the time, place, and circumstances of events; often lost in amnesia

Procedural memory (implicit)

Ability to recall a movement sequence or how to perform some act or behavior

Learning set

Rules of the game; implicit understanding of how a problem can be solved with a rule that can be applied in many different situations.

Implicit information is processed in a

bottom-up or data-driven manner, Information is encoded in the same way it was perceived

Explicit information is processed in

in a top-down or conceptually driven manner, subject reorganizes the information before it is encoded

Task roles in implicit tasks

passive role

Task roles in explicit tasks

active role

Priming

• Uses a stimulus to sensitize the nervous system to a later presentation of the same or a similar stimulus often used to measure implicit memory

Short-term memory

Information is held in memory only briefly, then discarded; involves the frontal lobes.

Long-term memory

Information is held in memory indefinitely, perhaps for a lifetime; involves the temporal lobe

Jeffrey Binder and colleagues (2009)

Found a distinct network comprising seven different left-hemisphere regions, including regions of the parietal lobe, temporal lobe, prefrontal cortex, and posterior cingulate cortex

Autobiographical memory

Episodic memory for events pegged to specific place and time contexts

Discriminability in the hippocampus:

Similar for old and new memories

Discriminability in the prefrontal cortex:

Much poorer for new memories

Hippocampal injury is also associated with

poor episodic memory

Increased __ activity during memory retrieval was found as a result of partial compensation for the hippocampal dysfunction

vmPFC

Highly superior autobiographical memory (HSAM)

People display virtually complete recall for events in their lives, usually beginning around age 10

Individuals with HSAM (Lawrence Patihis and colleagues, 2013)

Areas likely as other participants to develop false memories, Show superior personal memories but not superior cognitive functioning

William Scoville performed a bilateral medial temporal lobe resection on a young man, Henry Molaison (H. M.).

lacked explicit memory, retained implicit memory

Primary structures for explicit memory

Medial temporal region, Prefrontal cortex

Parahippocampal cortex

Receives connections from the parietal cortex, visuospatial processing

Perirhinal cortex

Receives connections from the visual regions of the ventral stream, visual object memory

Entorhinal cortex

Receives projections from parahippocampal and perirhinal cortices, first area to show cell death in Alzheimer disease

Visuospatial memory

Using visual information to identify an object’s location in space

Place cells discharge when rats are

in a spatial location, regardless of orientation

Head direction cells discharge whenever a rat’s

head points in a particular direction

Neocortex projects to the __, which projects back to the neocortex.

entorhinal cortex

Korsakoff Syndrome

Permanent loss of the ability to learn new information (anterograde amnesia) and to retrieve old information (retrograde amnesia)

what is Korsakoff Syndrome caused by

diencephalic damage from chronic alcoholism or malnutrition that produces a vitamin B1 deficiency

Mortimer Mishkin and his colleagues

Neural circuit for explicit memory incorporates evidence from both humans and laboratory animals with injuries to the temporal and frontal lobes

The temporal lobe role in memory

central to long-term explicit memory formation

The prefrontal cortex role in memory

central to maintaining temporary (short term) explicit memories and memory for the recency (chronological order) of explicit events

Hippocampus

consolidates new memories

consolidation

stabilizing a memory trace after learning, memories move from hippocampus to diffuse regions in the neocortex

Mishkin and colleagues (1982, 1997)

Proposed circuit for implicit memory: Basal ganglia, Ventral thalamus , Substantia nigra, Premotor cortex

where does the basal ganglia send projections to after recieving input from the neocortex

first to the ventral thalamus and then to the premotor cortex

why are explicit memories conscious

medial temporal lobe projects back to the cortex

Emotional memory

Memory for the affective properties of stimuli or events

two forms of pavlovian conditioning that are common in experiments today

eyeblink conditioning and fear conditioning

key regions associated with how autobiographical memories are stored in the brain

ventromedial prefrontal cortex (vm PFC) and hippocampus

Karl Lashley

began searching for the neural circuits underlying memories

Lashley discovered that severity of memory disturbance was related to not the location of the lesion but the

size

what type of memory deflicit is related to basal ganglia dysfunction?

implicit memory

Case H.M: bilateral medial temporal lobe resection

disrupting explicit memoru, implicit left in tact

structures involved in explicit memory

hippocampus, amygdala

two major neuronal changes that take place in Alzheimer disease

loss of cholinergic cells in basal forebrain, development of neuritic plaques and tangles in cerebral cortex

alzheimers disease is characterized by two misfolded proteins:

Amyloid-beta and tau

visual-recognition task

animal must learn to displace the novel object for the food reward