Lecture 7 - Memory: varieties & mechanisms (Cognitive Neuroscience, UU)

Representations: somehow the world is represented in the mind and the brain.

Churchland & Sejnowski: the defining function of nervous systems is representational.

Stored representations are believed to depend on the configuration of weights between units. In neural terms, these weights are the strength of synaptic connections between neurons.

Some memory functions are intact in amnesic patients.

• The declarative memory is impaired --> specific events
• Procedural memory often intact --> skills

Non-declarative (implicit) memory: memory without awareness. Skill learning, priming, classical conditioning.

Priming tests consist of:

• Free recall
• Cued recall
• Completion

Classical conditioning: before conditioning, the animal responds to the US, but not to the CS. At this stage, this is called the unconditioned response or UCR. During the conditioning the CS and the US are paired repeatedly. Conditioning leads to a conditioned response.

Delay vs trace conditioning in amnesic patients

• Delay: involve procedural memory, is not impaired in amnesic patients
• Trace: declarative memory; awareness, is impaired in amnesic patients

Anterograde amnesia: amnesia for events after the trauma

Retrograde amnesia: amnesia for events before trauma

Hebb: there is simultaneous activity in two neurons.

Changes in the effectiveness of synaptic transmission take place as a result of simultaneous pre- and postsynaptic activity.

There are two research strategies for neurobiology of learning and memory:

1. Top-down: presupposing a certain principle
2. Bottom-up: no presuppositions about the mechanism, but attempts at localization.

Top-down approach of LTP (long term potentiation) and memory.

• LTP: single stimulation of perforant path fibres to dentate gyrus results in an EPSP.
• After a brief tetanus (high frequent pulse; 250 Hz) the characteristics of the EPSP have changed.

NMDA receptor: neurotransmitter can bind to this. But there is a (Magnesium) block. This can be removed by depolarizing the cell. So it requires two simultaneous events: 1. Depolarization 2. Glutamate in the cleft.

Bottom-up approach: imprinting. The formation of early social preference for the mother or another stimulus.

Memory formation involved structural changes in the connections between neurons. Such structural changes involve protein synthesis.

Conclusions:

• Brain damage (MTL) causes amnesia
• Lead to distinction between different kinds of memory, incl. declarative memory and procedural memory
• A number of different brain structures are involved in human memory
• There are top-down and bottom-up approaches
• Bottom-up has the best prospects for localization of the neural substrate for memory
• Memory formation involves structural changes at the level of the synapse

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