L6 Neurons/memory

Question 1

substrates for persistent activity (memory storage)

Answer 1

• basal ganglia-thalamcortical loops
• Reciprocal loops between cortical areas
• Local recurrent excitatory cortical network
• Biophysical – graded stability of membrane potential to brief inputs

Question 2

what is the neuropharmacology of persistent cortical activity

Answer 2

certain neurons fire in a delayed match-sample task - responsible for STM encoding?
NMDA blockers prevent…
also activation of D1 receptors
evidence suggests synergism between L-Glu (NMDA) and DA systems - not effective alone

Question 3

how is a memory represented?

Answer 3

by a subset of pyramidal neurons firing in synchrony!!!

Question 4

what is the binding problem? how is it solved?

Answer 4

how it can work that these different, small aspects or features are linked together to create a larger internal representation/perception
solved by gamma/theta

Question 5

What is sequencing

Answer 5

organisation of persistent cortical activity
- sequence presented over 5-9 gamma cycles
- repeated over several theta cycles

Question 6

what do theta/gamma do

Answer 6

• Gamma oscillation ensures the precise time of firing in a subset of pyramidal neurons through fast membrane potential depolarisation
• Theta oscillation – a carrier wave that organises info about a moment in time and synchrony across hippocampus and other cortical areas

Question 7

how do theta/gamma operate?

Answer 7

• both gamma and theta depend on local feedback GABAergic inhibition and rhythmic IPSP input to ensure timing
• also theta is extrinsic - can be driven by other oscillators outside the hippocampal formation

Question 8

what other oscillators use theta

Answer 8

• entorhinal cortex - glutamatergic input
• medial septal nucleus (MSn) and diagonal band of Broca (DBB) - both mixture of GABAergic and cholinergic inputs

Question 9

what is Hebb’s rule

Answer 9

if repeatedly active at same time association will form
LTP needs sustained pre and post synaptic activation to increase synaptic efficiency

Question 10

How do associated memories activate each other?

Answer 10

bidirectional connections between nodes are initially weak, but automatically strengthened by conjoined activity
- image recognition software uses this
- only connections between active nodes strengthened
- can be activated by an input that only activates a few nodes, and ends up activating the rest of the network
CAN STILL HAPPEN WITH DEGRADED PATTERN