The Mind's Machine: Chapter 13

Learning and memory

Retrograde amnesia

loss of memory prior to an event (such as surgery or trauma)

Anterograde amnesia

inability to form new memories after an event (such as surgery or trauma)

Henry Molaison (Patient HM)

In this patient’s case, most old memories remained intact, but he had difficulty recollecting any events that took place after his surgery. Also unable to retain any new material for more than a brief period. Case provided clear evidence that short-term memory differs from long-term memory.

Hippocampus

Part of brain’s limbic system. Involved in memory, learning, and emotion. Its largest job is to hold short-term memories and transfer them to long-term storage in our brains.

Declarative memory

Facts and information acquired through learning. It is memory we are aware of accessing, which we can declare to others. Tests for this take the from of requests for specific info that was learned previously. Used for “what” questions.

Nondeclarative memory

AKA procedural memory. Memory about perceptual or motor procedures that is shown by performance rather than by conscious recollection. Examples include riding a bike. Used for “how” problems and is often nonverbal.

Delayed non-matching-to-sample task

A test of object recognition that requires monkeys to declare what they remember by identifying which of two objects was not seen previously.

Patient NA

Shown anterograde amnesia since his accident, but can recall earlier events. MRI showed damage to several limbic system structures in the medial diencephalon that have connections to the hippocampus: the dorsomedial thalamus and mammillary bodies.

Dorsomedial thalamus

Plays a crucial role in attention, planning, organization, abstract thinking, multi-tasking, and active memory.

Mammillary bodies

Primary function is recollective memory. Assumed that they act as a hippocampal relay.

Korsakoff’s syndrome

Degenerative disease in which damage is found in the mammillary bodies and dorsomedial thalamus, but not in temporal lobe structures like the hippocampus. People with this syndrome often fail to treconize or sense any familiarity with some items, even those presented repeatedly, yet frequently they deny that anything is wrong with them. They often confabulate (fill in a gap in memory with a falsification they accept as true) probably caused by damage to frontal cortex.

Patient KC

Could no longer retrieve any personal memory of his past, although his general knowledge remained good. Could play a game of chess, but could not recall where he learned to play or who taught him. Could not acquire new episodic knowledge. Inability to recall autobiographical details may be consequence of injury to frontal and parietal cortex.

Episodic memory

Detailed autobiographical memory. When you recall a specific episode in your life or relate an event to a particular time and place.

Skill learning

Process of learning how to perform a challenging task simply by doing it over and over. (ex. improving at the mirror-tracing task performed by HM or learning to read mirror-reversed text)

Basal ganglia

Refers to a group of subcortical nuclei responsible primarily for motor control, as well as other roles such as motor learning, executive functions and behaviors, and emotions.Skill learning impaired in people with damage to this structure.

Priming

A change in the way you process a stimulus, usually a word or a picture, because you’ve seen it, or something similar, previously. Priming does not require declarative memory of the stimulus. Not impaired by damage to basal ganglia.

Associate learning

Learning that involves relation between events (ex. between two or more stimuli, between a stimulus and a response, or between a response and its consequence)

Classical conditioning

In this form of associative learning, an initially neutral stimulus comes to predict an event.

Pavlov’s dog experiment: Repeatedly ringing a bell before putting meat powder in a dog’s mouth will eventually cause the dog to start salivating when it hears the bell alone. In this case the meat powder in the mouth is called the unconditioned stimulus (US), which already evokes an unconditioned response (UR; salivation in this example). The sound of the bell is called the conditioned stimulus (CS), and the learned response to the CS alone (salivation in response to the bell) is called the conditioned response (CR).

Operant/instrumental learning

An association is formed between the animal’s behavior and the consequence of that behavior.

Skinner box: In a common setup, the animal learns that performing a certain action (pressing a bar) is followed by a reward (such as a food pellet).

Cerebellum

Primarily responsible for muscle control, including balance and movement. Also plays a role in other cognitive functions such as language processing and memory. Circuits in this structure are crucial for simple eye-blink condiitoning.

Place cells

Neurons that selectively encode spatial location. Crucial in forming a cognitive map (an understanding of the relative spatial organization of objects and information).

Neuroplasticity

The ability of neural networks in the brain to change through growth and reorganization.

Semantic memory

Generalized declarative memory, such as knowing the meaning of a word without knowing where or when you learned that word.

Environmental enrichment/impoverishment & dendrites

Synaptic plasticity & habituation

Ability of neurons to modify the strength of their connections, especially important after damage. Habituation is a type of nonassociative plasticity in which neural responses to repeated, neutral stimuli are suppressed over time.

Hebbian synapse

Hebb proposed a theory that neurons that fire together, wire together. Proposed that when a presynaptic and postsynaptic neuron were repeatedly activated together, the synapatic connection between them would become stronger and more stable.

Long-term potentiation (LTP): outcome, physiologically (i.e., change in firing rates)

Complex process leading to persistent strengthening of synapses that enables a long-lasting increase in synaptic transmission in a neuronal network.

LTP: mechanism, structurally

LTP appears to have the hallmarks of a cellular mechanism of memory: a long-lasting change in synaptic strength.

LTP & NMDA receptors

The most studied form of LTP occurs at synapses that use the excitatory neurotransmitter glutamate, and it is critically dependent on a receptor subtype called the NMDA receptor. Treatments with drugs that selectively block NMDA receptors completely prevents LTP in this region, but doesn’t affect synaptic changes that have already been established. NMDA receptors are fully active only when “gated” by a combination of strong depolarization (via AMPA receptors) and the ligand (glutamate)

LTP & AMPA receptors

During normal, low-level activity, the release of glutamate at the synapse activates only the AMPA receptors, so the EPSP is mediated entirely by these AMPA receptors. The NMDA receptors cannot respond to glutamate because magnesium ions block the NMDA receptors calcium ion channel.