Intro to Neural circuits of Cognition

Question 1

Cognition def (1)

Answer 1

any form of mental operation or intellectual activity, such as thinking, reasoning, imagining, learning or remembering

Question 2

learning def (1)

Answer 2

the acquisition of new information or knowledge

Question 3

Memory def (2)

Answer 3

the storage and retrieval information

Memory has temporal stages: short-term, intermediate-term and long-term

Question 4

Engram def (1)

Answer 4

the physical substrate of a memory (i.e. the brain cells and their connections that store a memory)

Question 5

LT memory classification (7)

Answer 5

declarative or non-declarative:

Decl:
–episodic: Specific (i.e. event based) memories - eg Remembering your first day of university
– semantic: non-specific (generalised, fact based) memories - eg knowing capital cities

non-decl:
– procedural: skill learning eg riding bike
– associative: stimulus = response eg classical conditioning
– non-associative: habituation + sensitisation eg sleeping through planes noises

Question 6

cell assembly hypothesis (6)

Answer 6

• theory of how information is processed and stored in the brain

1) all the neurons activated by that experience/stimulus = cell assembly

• all cells reciprocally interconnected
• held in ST memory
• if it continues = growth process that strengthens reciprocal connections (fire together, wire together)

strengthening of connections = a subsequent stimulus that is only capable of activating a proportion of the neurons in the assembly can still cause the entire assembly to be reactivated

Question 7

Amnesia def + 2 types (3)

Answer 7

The loss of the ability to learn and remember, typically caused by damage to the brain resulting from injury or disease

2 main types:
(1) Retrograde amnesia – loss of memory for events in the past (i.e. before brain trauma)

(2) Anterograde amnesia – loss of the ability to form new memories after brain trauma

Question 8

Patient H.M. (6)

Answer 8

-developed severe epilepsy after bicycle accident

• 1953: had an operation to remove part of his medial temporal lobe = cured his epilepsy but left him with partial retrograde and severe anterograde amnesia
• wasn’t able to form new declarative memories for events after the operation
• He also lost memories for events in the years leading up to the operation

But…
* His memories from early life events (e.g. his childhood) were intact
* He was still able to learn procedural tasks

Question 9

What do we learn about memory from Patient HM? (2)

Answer 9

➢ The medialtemporal lobes are needed to form new declarative memories

➢ The neural circuits involved in declarative and procedural memory, and recent and latent (i.e. a long time ago) memory storage are not
necessarily the same

Question 10

Alzheimer’s disease (3)

Answer 10

• the most common cause of dementia - a syndrome disrupts a person’s cognitive abilities.
• key symptom = the loss of declarative memory ability
• A core pathological feature = the build-up of aggregates of protein that cause neurons to die in the medial temporal lobes

Question 11

AD loss of memory stages (2)

Answer 11

Early AD → anterograde amnesia (cannot form new declarative memories)

Later → retrograde amnesia (with memories of most recent events lost first)

Question 12

medial temporal lobe - structures for memory (4)

Answer 12

A group of brain structures in the medial temporal lobe crucial for processing declarative memories.

Key structures are:
(1) The hippocampus
(2) The entorhinal cortex
(3) The perirhinal cortex
(4) The parahippocampal cortex

Question 13

Proposed functional organisation of the medial temporal lobe memory system - 3 steps (3)

Answer 13

image
1) association cortices:
what -> Perirhinal cortex
where -> parahippocampal cortex

2) peri -> lateral entorhinal = item
para -> medial entorhinal = context

3) all to hippo = item in context

Question 14

Memory processing in the diencephalon (5)

Answer 14

The diencephalon is (mainly) composed of the thalamus and hypothalamus

• These structures also play a key role in
  processing declarative memories

Key parts of these structures are:
* Anterior nuclei of the thalamus
* Dorsomedial nuclei of the thalamus
* Mammillary bodies of the hypothalamus

Question 15

Explain the thalamus works as an information relay (3)

Answer 15

The thalamus + hypo receive inputs from ‘memory structures’ in the medial
temporal lobes (hippocampus, entorhinal cortex, perirhinal cortex).

The anterior and dorsomedial nuclei of the thalamus send outputs to almost all of frontal cortex

image:
1) medial temporal lobe structures ->

2) (fornix) -> hypo -> anterior nucleus of thal ->
-> dorsomedial nucleus of thal ->

3) -> cingulate cortex
-> frontal cortex

Question 16

Patient N.A. (4)

Answer 16

• suffered a penetrating brain injury being stabbed him through the nose with a fencing foil!
• = a selective lesion of N.A.’s left dorsomedial thalamus and mammillary bodies
• The lesion caused severe anterograde amnesia, and retrograde amnesia for events up to 2 years before the accident
• N.A.’s amnesia was very similar to that in patient H.M.
  = suggests that connected neural circuits in the medial temporal lobes and diencephalon form part of a system for forming declarative memories

Question 17

Spatial memory def (1)

Answer 17

memory of locations and the relationship between positions in a location

Question 18

What is the role of the hippocampus in spatial memory?(3)

Answer 18

Several key pieces of evidence show the importance of the hippocampus in processing spatial memories.

(1) Lesions/inactivation of the hippocampus impairs spatial learning and memory

(2) Places are encoded (internally represented) by the activity of hippocampal neurons

Question 19

Evidence that hippocampal lesions impair navigation (2)

Answer 19

Morris Water Maze:
A test of spatial reference memory – ‘what’ and ‘where’ things are in an environment.

Rodents with lesions of the hippocampus perform at chance levels in water maze

Question 20

What other hippo manipulation impairs spatial navigation memory in MWM? (2)

Answer 20

Infusing drugs that block NMDA receptors into the hippocampus also blocks spatial reference memory in the water maze

(NMDAr = crucial for synaptic plasticity and therefore cell assembly formation)

Question 21

Place cells (4)

Answer 21

• The activity of excitatory cells in the hippocampus is tuned to spatial locations i.e. the cells fire in specific places.
• These neurons are called place cells.
• Place cells act like the brain’s GPS.
• found in hippocampus

Question 22

Explain how place cell activity generates a cognitive map - rat (4)

Answer 22

The collective activity of many place cells forms a complete mental(cognitive) map of an environment

eg 80 heat maps, showing the firing locations of 80 hippocampal neurons recorded at the same time as
a rat explored a 1m x 1m box

• Hotter colours = higher firing rates.
• The activity of ~30% of the cells is tuned to a specific location in the box
• The activity of place cells is a suggested to be a neural substate for spatial learning and memory

Question 23

Place cells in the human brain experiment (3)

Answer 23

Recorded from individual neurons in the hippocampus in human neurosurgery patients navigating around a virtual reality maze

= heat map created

Question 24

Where does consolidation of declarative memories take place? (3)

Answer 24

evidence suggests that the LT consolidation (storage) of episodic and semantic information occurs in the association cortices

eg Patients HM + NA:
→ Severe anterograde amnesia.
→ Graded retrograde amnesia for recent events

According to hypothesis, the hippo works initially with cortex to encode new memories

Through a gradual process of reorganisation (involving the hippo + thalamus), connections b/w neurons in
cortical regions are strengthened until the memory can be accessed independently of the hippocampus

Question 25

How does replay of experience dependent neuronal activity supports memory consolidation? - experiment (3)

Answer 25

‘Online’ state → Running along a linear track : Sequential activation of place cells in the hippocampus

some time later…

‘Offline’ state → Rest or sleep : Offline reactivation (‘replay’) of the place cell sequence on a compressed timescale

current hypothesis = that the replay of coherent memory traces between the hippocampus and cortex enables LT memory consolidation

Question 26

Striatum regions + memory (4)

Answer 26

• it’s important for non-declarative memories
• The striatum is part of the basal ganglia
• It’s involved in motor planning and
  generating movements

It consists of:
(1) The caudate nucleus
(2) The putamen

Question 27

Evidence for the role of the striatum in procedural memory (4)

Answer 27

Win-stay task:
- rats need to learn simple procedure
=> must enter arms of maze that are lit = food reward
- rat does not need to remember where it is (i.e. no spatial memory) – just to enter the lit arms

Rats with lesions of the medial temporal
lobe/diencephalon (the fornix) can learn this task

Rats with lesions of the striatum cannot learn this task i.e. they keep entering arms of the maze that are not lit.

Question 28

Evidence for the role of the striatum in associational memory pt 1- PD (2)

Answer 28

Parkinson’s disease:
- caused by the degeneration of dopaminergic inputs from the substantia nigra into the striatum

• This not only impairs patients’ ability to initiate movements, but also disrupts their ability to form procedural and associational memories

Question 29

Evidence for the role of the striatum in associational memory pt 2- Evidence (4)

Answer 29

Knowlton et al 1996:

• Tested Parkinson’s and amnesia (people with MTL or diencephalon damage) patients’ ability to form stimulus- response associations
• patients had to learn to associate certain sequences of cards with an arbitrary prediction of sunny or rainy weather
• Patients w/ amnesia could do this task, but had very poor declarative memory ability on a subsequent test
• Patients w/ PD could not do this task, but had normal declarative memory ability on a subsequent test