lecture 5 - cellular and system-level memory consolidation

Question 1

types of memory consolidation

Answer 1

1. cellular (synaptic)

2. system-level (whole brain)

Question 2

define memory consolidation

Answer 2

‘offline neural changes that lead to memory stabilization, enhancement, and integration with pre-existing knowledge.’

Question 3

what is the ‘clay sculpture’ metaphor?

Answer 3

Wixted & Cai 2014

Memory initially at its finest, but fragile; over time, it becomes resistant to interference, I.e., it is shows less and less potentials for damage.

Question 4

what is cellular consolidation?

Answer 4

Occurs at the neuron level (not at the whole-brain “systems” level)

Takes place during the first hours (and perhaps days) after initial memory formation in the hippocampus

Fits well with the idea of a trace-hardening physiological process put forward as far as Mueller and Pilzecker

Corresponds to the discovery of long-term potentiation (Bliss & Lømo, 1973)

Question 5

Long term potentiation – Bliss & Lomo 1973

Answer 5

Long-lasting enhancement of synaptic efficacy induced by a tetanus (short burst of high-frequency stimulation) to the presynaptic neuron.

Question 6

Retrograde facilitation -

Answer 6

If subsequent encoding (mental exertion) interferes with memory consolidation, then factors blocking new encoding should promote memory stabilization.

Question 7

systems consolidation

Answer 7

HM’s bilateral medial temporal lobe (MTL) resection:

• (1) anterograde amnesia: inability to form new declarative memories (the ‘what’)
• (2) temporally graded retrograde amnesia: impairment of memories formed prior to surgery, stronger for young than old memories (Scoville & Milner, 1957) (Ribot’s law, 1881).

Declarative memories becoming independent from the hippocampus and more dependent on the neocortex is referred as ‘systems consolidation’.

The hippocampus

Question 8

What is the significance of this shift of activation from the medial-temporal lobe to the neocortex?

Answer 8

Declarative memories stored in neocortex from the outset (e.g., sensory and semantic areas)

Hippocampus acts as a relay station and binds them together.

Over time, cortico-cortical associations develop, such that these memories become independent of the hippocampus.

Question 9

complementary learning systems

Answer 9

a) A fast learning system that holds information only temporarily (medial temporal lobe, i.e., the hippocampus)
b) A slow learning system that serves as long-term store (i.e., the neocortex)

Question 10

complementary learning systems - main idea

Answer 10

• Information initially stored in the hippocampus is progressively fed back into the neocortex (via ‘neural replay’), so that pre-existing knowledge can accommodate newly learnt information. The hippocampus is seen as the internal sparring partner of the neocortex.
• As both systems are used to encode new learning, this reactivation/redistribution has to occur offline, for instance during sleep.