1. Neural Coding and Function of Hippocampus

Question 1

patient H.M.

Answer 1

• started the investigation into different brain regions playing different roles
• bilateral removal of medial temporal lobes and hippocampus
• anterograde and slight retrograde (before) amnesia
• lots of cortex affected as well

Question 2

what memory are we focusing on?

Answer 2

declarative memory

Question 3

declarative memory

Answer 3

past events - experience it once and are able to remember again
- medial temporal lobe - diencephalon

Question 4

can we study cognitive abilities in animals?

Answer 4

• many people have argued the importance of the cortex for cognition (Kirsch et al, 2008) - complex make up with 6 layers of neurons all projecting to other layers (PFC too)
• animals have impressive cognitive abilities even without a cortex - ‘insight related cognition’
• animals may show simple precursors to higher order cognition and episodic memory

Question 5

animal models

Answer 5

• cases like H.M. are rare and we cant study in humans because its unethical
• can use more invasive techniques in animals/human studies methodology is limited

Question 6

scala naturae

Answer 6

• ladder of being (simple > complex)
• similar in terms of evolution in the brain
• birds and mammals 300 million years apart/birds don’t have cortex but we do
• to see if the cortex is responsible for higher cognitive function, test that in an animal with no cortex (bird)

Question 7

Prior (2008) - concept of themselves

Answer 7

does a magpie recognise its self in the mirror?

• the bird acts aggressive thinking it is another rival bird
• suggests no theory of mind
• however, other magpies look behind the mirror knowing it is not another bird - similar to child’s ToM

Question 8

contingency testing

Answer 8

some birds make specific movements to see how the mirror responds
- knows its not a rival bird

Question 9

tool use

Answer 9

Weir et al., (2002) - bird presented with a straight wire and out of reach grub > bird bends wire to hook it out of tube

Bird et al., (2009) - uses stones to displace water so floating grub becomes in reach

Question 10

hippocampus

Answer 10

• cells might do different things depending on sub region
  curved shape from central to lateral part of brain
• described as a tri-synaptic pathway as it contains the perforant pathway, mossy fibres, Schaffer collaterals
• subregions: dentate gyrus, CA3, CA1, Subiculum
• contains projection and inhibitory interneurons

Question 11

Dentate gyrus/Perforant pathway

Answer 11

• input path/location of the hippocampus from dentate gyrus
• densely packed with granule cells
• many different interneurons
• prominent in neurogenesis (new cell formation) - function of new memories?

Question 12

are granule cells excitatory or inhibitory?

Answer 12

excitatory projection neurons

Question 13

projection neurons

Answer 13

across subregions

project to next part (e.g. dentate gyrus to CA3)

Question 14

inhibitory interneurons

Answer 14

within a subregion

- connect neurons within one of the subregions (e.g. within dentate gyrus)

Question 15

CA1 and CA3

Answer 15

• hippocampus proper (main area) - complex structure
• complex network of of pyramidal neurons and inhibitory interneurons (differ in type of dendrites, where they project to, what they project to)
• there is a continuous path of pyramidal neurons (multipolar neurons) > primary excitation units of mamalian PFC - dense recurrent network in CA3
• lots of interneurons at each region (CA3 - pyramidal neurons that connect to each other - formation of memories?)
• overall you see a tri-synaptic pathway
• many cannabinoid receptors - link between weed and poor memory

Question 16

tri-synaptic pathway

Answer 16

input from perforant pathway through dentate gyrus - axons of these neurons (mossy fibres) project to CA3 - pyramidal neurons here project to CA1 - continues to subiculum

Question 17

subiculum

Answer 17

• • output region of the hippocampus
• two types of principle neurons:
  1) regular firing = consistent firing of AP’s
  2) bursting neurons = fire AP’s in bursts
• very central brain location so hard to study

Question 18

hippocampal formation

Answer 18

• part of the limbic system
• main inputs and outputs are in terms of entorhinal cortex which sits underneath hippocampus
• perforant pathway = layer II of entorhinal cortex to CA3
• tempero-ammonic pathway = layer III of entorhinal cortex to CA1
• entorhinal cortex projects to different regions (temporal lobe > entorhinal cortex > hippocampus - towards centre of brain)
• have dendritic trees that extend to both sides of input location
• gives you an idea of the complexity when trying to study specific neurons in this location

Question 19

electrophysiology

Answer 19

• measure the flow of ions in the brain with electrodes
• from recorded signal we can determine when an AP was elicited by a neuron
• results in spike trains (identifying neural activity) - key to linking neuronal activity with behaviour

Question 20

neuronal coding

Answer 20

AP reflect sensory perceptions, cognitive functions and behaviour
- RATE CODING = number of spikes in a time window (usually per second - Hz)

Question 21

rate coding

Answer 21

cognitive function represented in AP’s

• can look at the neural coding of individual neurons and compare them (could be related or random)
• can also see whether different neurons fire simultaneously or are correlated (e.g. one fires and another fires slightly after/is excited)
• could fire when animal in specific locations of sees a stimulus of a specific orientation (Hubel and Wiesel)
• Hafting et al (2005)

Question 22

Hafting et al (2005)

Answer 22

• rat in a box
• black lines showed its walking pattern around the box
• electrode placed in entorhinal cortex
• red dots resemble where this neuron elicited an AP
• shows clusters of activity in specific locations
• if you know the neural activity you can identify where the rat is located in the box (DECODING FROM AP’S)