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Models of Brain Function > Week 4: A case study using rate neurons = Head Direction (HD) Cells > Flashcards

Week 4: A case study using rate neurons = Head Direction (HD) Cells Flashcards

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1
Q

HD Case study using

A

rate-coded neurons

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2
Q

Hippocampus and its nearby areas are important for

A

memory and spatial cognition/orientation

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3
Q

spatial cognition means….

A

the knowledge and processes used to represent and navigate in and through space

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4
Q

First hint that hippocampus important for memory formation is from famous case study H&M as… (3)

A

· HM had severe epilepsy that was drug resistant

· At the last resort, they cut both hippocampi (since hippocampus is typically the source of epileptic seizures)

· They figured out that HM could not form any new memories

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5
Q

A parallel stream of animal research (after H&M) using the Morris Water maze also revealed that the

A

hippocampus is fundamental for spatial navigation.

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6
Q

What does the Morris Water maze involve? (3)

A

rodents placed in a pool of water that is opaque

· The maze has a hidden escape platform that is just below the surface of the water and is in a fixed location of the maze.

· In the maze, the animals must search to locate the hidden platform

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7
Q

Morris Water Maze

Findings (Morris et al., 1982)

A

Rats who had no lesions to the hippocampus (control) took less time in swimming towards the platform , no matter what area they were dropped in the maze, as compared to rats who had bilteral lesions to the hippocampus.

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8
Q

Diagram of Morris Water Maze

A
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9
Q

Taube 1990 measured the neurons in the hippocampus and surrounding areas using a technique called

A

single cell recordings mostly with rodents

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10
Q

Single cell recordings methodology (3)

A

microdrives with electrodes are implanted chronically in rodents’ brain

·Once the animal recovered from this surgery, the rodent is allowed to remove freely from the box where there is a visual cue (e.g., white cue card) on the wall of the box which helps the animal orient itself to

The electrodes in the animal are moved slowly per day until they record spikes:

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11
Q

Single cell recordings technique allows us to know

A

what single neurons are doing in a behaving animal

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12
Q

Diagram of rodent single cell recordings

A
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13
Q

Cells that share characteristics of encoding both place and HDC found in

A

Presubicular and parasubicular cortices (Taube, 2007)

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14
Q

Plot of HD cells

A
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15
Q

Head directions are predominantly found in a large network of brain areas in Papez circuit (Taube 2007) such as (3)

A

o Entorhinal cortex
o The thalamus (lateral dorsal and anterior dorsal nuclei)
o Anterior dorsal thalamic

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16
Q

HD found in non-Papez circuit in brain like (3) (Taube, 2007)

A

Lateral dorsal thalamus
Dorsal striatum
Medial preecentral cortex

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17
Q

Diagram of areas where HD cells are found: what red, blue and green? (3)

A

Red = Pure forms of head direction cells

Green = Theta-modulated head directions

Blue = Theta-modulated structures that have no head direction cells

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18
Q

Reminder of theta is:

A

distinguished background oscillation in the membrane potential (similar to VoSC in the Lisman and Idiart model of WM)

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19
Q

Place cells are commonly found in the (2)

A

· subiculum and

in the entorhinal cortex ( Taube, 2007)

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20
Q

Two types of cells important for spatial cognition (2)

A

HD cells

Place cells

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21
Q

The general properties of HDC was first described by

A

Taube et al., 1990

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22
Q

HDCs can be depicted using a (2)

A

polar plot or

tuning curve with firing rate on ordinate axis and animal’s head represented on abscissa

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23
Q

Taube et al., (1990) HD cell Tuning graph (3) Example

A

Graph from single cell recording that is integrated over time

Animal will run around with box for 10-20 minutes where experimenters track where the animal is looking and firing rates of HD neurons

In this graph, a particular neuron emits few spikes at 90 degrees. But when animal is looking 200 degrees, every time during 20 minutes, this particular HD neuron vigorously emits more spikes (PREF DIREC)

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24
Q

Direction at which HDCs fire maximally is referred as the cell’s

A
  • preferred firing direction
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25
Q

Place cell graph (3)

A

Let animal run around the box

Every time a specific place cell neuron fires AP you plot a red dot

Accumulates this data over 20 minutes of rodent running in box

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26
Q

Receptive fields, areas at which

A

which stimulation leads to response of a specific sensory neuron”

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27
Q

Different place cells and HD cells are distinguished by

A

their different receptive fields

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28
Q

Place cells have a receptive fields for

A

spatial location

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29
Q

HD cells have a receptive field for

A

head orientation

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30
Q

Whats the 3 uses of HD cells?

A
  • Orientation is very important for navigation
  • For grasping and pointing: If you want to reorient yourself and do some action like pointing somewhere in a specific direction
  • To define a point of view = human spatial cognition
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31
Q

Different HD cells are distinguished by different receptive fields meaning in other words:

A

what direction is the preferred direction (i.e., emits most spikes)

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32
Q

In place cells have receptive fields meaning that a particular place cell neuron fires most

A
  • vigorously at a particular location in the environment
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33
Q

From manipulations of single-cell recording of rodent (Taube, 1990), experiments found 3 main defining properties of HD cells are… (3)

A

Head direction cells depend on vestibular input

Cue cards control angular turning

HD drift in darkness meaning without any visual input, the animal loses its sense of orientation

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34
Q

Mizumori and Williams (1993) found HD cells drift in darkness as when rats are either blindedfolded or placed in complete darkness then preferred direction of HD cells

A

become less stable (disrupted) and begins to drift

35
Q

Stackman and Taube (1997) found HDcs depend on vestibular input as

A
  • neurotoxic lesions of vestibular labyrinth abolished HD cell signal in the AND for up to three months post lesion
36
Q

vestibular input is the sensation in

A

changes of direction, movement and position of head

37
Q

Taube demonstrated that the cue cards control angular turning (orientation)

what was the method?

Rotate cue card leads to…

This means HD is controlled by… (3)

A

HD cells recorded in a cylinder that contains a prominent visual cue (e.g., white cue card) attached to the box

They rotate this important visual landmark which leads to a corresponding shift in the preferred firing direction of HD cells

Thus, HD cells controlled by landmarks (Taube et al., 1990

38
Q

Hypotheses from 3 main defining properities of HD cells (2)

A

HD used for navigation

When animal lost its way, HD cells have lost their stable directional tuning which makes them drift

39
Q

Correct for drift in HD cells by

A

receiving feedback from visual cue

40
Q

Correct for drift in HD cells by receiving feedback from visual cue

What is visual cell and seeing visual cue card ahead? (2)

A
  • Visual cells that are somewhere in your visual cortex will provide feedback (i.e., meaning providing synaptic inputs at particular orientations to specific HD cells)
  • In seeing a cue card ahead, a specific visual cell will be active and give strong synaptic input to the appropriate and correct HD cell
41
Q

Diagram of visual cells feedback correcting for drift

A
42
Q

Even in darkness, the directional firing preference of HDC was maintained - Mizumori and Williams 1993

A

briefly

43
Q

Another property of HDcs is independent of animal’s ongoing behaviour in experiment as

A

The firing of a head direction cell was maximal at the preferred direction and unaffected by whether the animal was eating, grooming, earing, walking running etc..

44
Q

Questions for HD cells model (2)

A

How is HD activity sustained when head is still at a certain heading and even without any visual inputs (i.e., darkness)

How is HD updated after each head turn?

45
Q

HD sustained firing at given location

Taube (2007;1990) found HDC firing is largely unaffected by pitch/roll of animal’s head within 90 degrees of horizontal plane as

A

long as the animal’s head is in a given cell’s directional range, cell firing will continue whether the animal is moving or still and largely independent of the animal’s ongoing behaviour

46
Q

HD cells must cover

A

0 to 360 degrees uniformly

47
Q

We get a tuning curve of a single HD cell neuron by (2)

A

As the animal moves around our chosen neuron fires at varying rates depending on the heading

Summing all those activities and dividing by the total time we get a tuning curve

48
Q

Diagram of tuning curve of single HD cell

A
49
Q

In a tuning curve of HD cell it has firing rate ______ as a function of ___

Its data is ____

(2)

A

firing rate of a single HD neuron as a function of heading

Its data is accumulated over time

50
Q

Tuning curve of all HD neurons given one heading diagram

A
51
Q

In tuning curve of all HD neurons there is line of bunch of

A

neurons

52
Q

In tuning curve of all HD neurons , the ___ HD neuron is active

A

red

53
Q

Tuning curve where updating heading and turning head to another direction diagram

A
54
Q

What happens when turning my head in another direction in tuning curve? (3

A

A different HD neuron is maximally active compared to other 2 graphs

Now that the heading is changed, the activity of HD cells is shifted so the red neuron is less active and gives smaller contribution to this orientation

As animal moves, tuning curve of firing rate of HDC shifts with different heading directions so different HDC get smaller or large contributions.

55
Q

The defining characteristic of this case study is finding the synaptic connections that give us (tuning curve pattern, more specifically…) - (2)

A

sustained activity when the head is still, even in darkness (at least for a while) i.e., without sensory feedback

Able to shift the activity pattern of HDCs across the line of neurons

56
Q

HDCs most active in a particular direction sustain their activity when the head is still (even in darkness) by…

short-range excitatory connections + long-range inhibitory connections (2)

A

It is exciting itself as well as exciting neighbouring HDC near them due to having short-range excitatory synaptic connections (recurrent connections)

Also has long-range inhibitory synaptic connections to distant HDC to suppress its activity

57
Q

Diagram of HDCs having short-range excitation and long-range inhibition

A
58
Q

There is close-range excitation and long-range inhibition for each

A

HDC neuron in the ring

59
Q

How to shift the activity pattern of HDCs across the line of neurons? (3)

A
  • These line of neurons active will have an offset inhibition in the direction opposite of a turn and offset excitation in the direction of a turn.
  • These connections will be active only when the head is turning (dependent on velocity)
  • We need double of these connections, one for clock-wise and counter-clockwise head turns.
60
Q

Diagram of shifting activity packet across ring of HDC neurons

A
61
Q

To turn clockwise we need to excite

A

nearby HDCs to the right (blue)

62
Q

To turn anti- clockwise we need to excite

A

nearby HDCs to the left (purple)

63
Q

Reminder: what gives us sustained activity for

A

symmetric short-range and long-range inhbition

64
Q

Reminder: what gives us capability to turn our head and shift activity pattern across ring of HDCs neuron?

A

Velocity-dependent asymmetric excitation and inhibition

65
Q

Paper that used firing rate model to explain spatial orientation in HDCs

A

Zhang et al., (1996)

66
Q

In Zhang’s paper, equation is:

A

change of activation over time = -a + (weight * rate)

67
Q

Zhang’s paper have W as a matrix

A

all sender/receiver combinations and r is a vector of firing rates of all neurons

68
Q

Some of the wij will be 0 so meaning in Zhang will be

A

zero, those for sender-receiver neuron pairs that are not connected by a synapse

69
Q

Zhang’s concise equation for each neuron in the network

A
70
Q

In Zhang’s concise equation, each equation needs to be updated

A

separately which was the case in lamprey spinal cord and WM model

71
Q

Updating orientation Zhang 1996
diagram (2)

odd weights lead to…

the asymmetric component is…

A

odd weights (call them asymmetric) lead to shift of the activity bump across the neurons

Recall the asymmetric component is velocity dependent

72
Q

Two possible behaviours when giving external stimulus to HD ring in Zhang 1996 model

A

Shift and reset

73
Q

Zhang found that the internal

A

direction maintained by HD cell networks is calibrated by external input from a local-view detector

74
Q

If the activity of HD cell network is maintained at 180 degrees but the heading is 200 degrees then the

A

external input from the local-view detector will induce a shift in its activity towards 200

75
Q

Reset is shown if the excitation of HD cells in the network is too far away from the actual orientation of heading then the

A

external input from the local-view detector will produce a new estimate –> this resets the heading.

76
Q

Diagram of reset and shift

A
77
Q

The HD ring network is an example of a

A

continuous attractor network (CAN)

78
Q

HD ring network is an example of CAN because… (3)

A

o Place the activity anywhere you wanted in our line of neurons

o Shift it and make it come to rest at a new position

o It can sustain its activity as connectivity pattern is same for each neuron when heading is still at a certain orientation

79
Q

If precise connections are perturbed? (like deleting some HDC cells) in ring of HDC then - (4)

A

All activity of HDCs converge to different locations and at the end only represent a subset of all possible orientations

The continous attractor becomes a discrete attractor

Certain HDC attract the activity bump

Discrete basins of attractions (circle)

80
Q

Continous attractor def and example (2)

A

we can place the ball anywhere

(our symmetric connections maintain the activity packet in place)

81
Q

Discrete attractor ball def and example (2)

A

Given a bit of time, the ball settles in one of
Several valleys (basins). Locations between valley are unstable.

Is this what happens to HD during aging due to neuron loss?

82
Q

Benefits of this HD (4)

A

Best model of HD we have

Allows us to explain how internal sense of direction is coded and maintained

Don’t have to make use of spikes, let alone ion channels (assuming all info about direction is encoded in firing rate of network)

Good case of rate-coded neurons

83
Q

Problems of HD CAN - (2)

A
  • How could the brain learn and maintain such precise connections? Neurons die off, affected by biological noise (e.g., temperature etc…)

o Partial answer: see reference Cacucci

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