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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

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
Place cell graph (3)
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
26
Receptive fields, areas at which
which stimulation leads to response of a specific sensory neuron"
27
Different place cells and HD cells are distinguished by
their different receptive fields
28
Place cells have a receptive fields for
spatial location
29
HD cells have a receptive field for
head orientation
30
Whats the 3 uses of HD cells?
- 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
31
Different HD cells are distinguished by different receptive fields meaning in other words:
what direction is the preferred direction (i.e., emits most spikes)
32
In place cells have receptive fields meaning that a particular place cell neuron fires most
- vigorously at a particular location in the environment
33
From manipulations of single-cell recording of rodent (Taube, 1990), experiments found 3 main defining properties of HD cells are... (3)
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
34
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
become less stable (disrupted) and begins to drift
35
Stackman and Taube (1997) found HDcs depend on vestibular input as
- neurotoxic lesions of vestibular labyrinth abolished HD cell signal in the AND for up to three months post lesion
36
vestibular input is the sensation in
changes of direction, movement and position of head
37
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)
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
Hypotheses from 3 main defining properities of HD cells (2)
HD used for navigation When animal lost its way, HD cells have lost their stable directional tuning which makes them drift
39
Correct for drift in HD cells by
receiving feedback from visual cue
40
Correct for drift in HD cells by receiving feedback from visual cue What is visual cell and seeing visual cue card ahead? (2)
- 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
Diagram of visual cells feedback correcting for drift
42
Even in darkness, the directional firing preference of HDC was maintained - Mizumori and Williams 1993
briefly
43
Another property of HDcs is independent of animal's ongoing behaviour in experiment as
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
Questions for HD cells model (2)
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
**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
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
HD cells must cover
0 to 360 degrees uniformly
47
We get a tuning curve of a single HD cell neuron by (2)
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
Diagram of tuning curve of single HD cell
49
In a tuning curve of HD cell it has firing rate ______ as a function of ___ Its data is ____ (2)
firing rate of a single HD neuron as a function of heading Its data is accumulated over time
50
Tuning curve of all HD neurons given one heading diagram
51
In tuning curve of all HD neurons there is line of bunch of
neurons
52
In tuning curve of all HD neurons , the ___ HD neuron is active
red
53
Tuning curve where updating heading and turning head to another direction diagram
54
What happens when turning my head in another direction in tuning curve? (3
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
The defining characteristic of this case study is finding the synaptic connections that give us (tuning curve pattern, more specifically...) - (2)
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
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)
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
Diagram of HDCs having short-range excitation and long-range inhibition
58
There is close-range excitation and long-range inhibition for each
HDC neuron in the ring
59
How to shift the activity pattern of HDCs across the line of neurons? (3)
- 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
Diagram of shifting activity packet across ring of HDC neurons
61
To turn clockwise we need to excite
nearby HDCs to the right (blue)
62
To turn anti- clockwise we need to excite
nearby HDCs to the left (purple)
63
Reminder: what gives us sustained activity for
symmetric short-range and long-range inhbition
64
Reminder: what gives us capability to turn our head and shift activity pattern across ring of HDCs neuron?
Velocity-dependent asymmetric excitation and inhibition
65
Paper that used firing rate model to explain spatial orientation in HDCs
Zhang et al., (1996)
66
In Zhang's paper, equation is:
change of activation over time = -a + (weight * rate)
67
Zhang's paper have W as a matrix
all sender/receiver combinations and r is a vector of firing rates of all neurons
68
Some of the wij will be 0 so meaning in Zhang will be
zero, those for sender-receiver neuron pairs that are not connected by a synapse
69
Zhang's concise equation for each neuron in the network
70
In Zhang's concise equation, each equation needs to be updated
separately which was the case in lamprey spinal cord and WM model
71
Updating orientation Zhang 1996 diagram (2) odd weights lead to... the asymmetric component is...
odd weights (call them asymmetric) lead to shift of the activity bump across the neurons Recall the asymmetric component is velocity dependent
72
Two possible behaviours when giving external stimulus to HD ring in Zhang 1996 model
Shift and reset
73
Zhang found that the internal
direction maintained by HD cell networks is calibrated by external input from a local-view detector
74
If the activity of HD cell network is maintained at 180 degrees but the heading is 200 degrees then the
external input from the local-view detector will induce a shift in its activity towards 200
75
Reset is shown if the excitation of HD cells in the network is too far away from the actual orientation of heading then the
external input from the local-view detector will produce a new estimate --> this resets the heading.
76
Diagram of reset and shift
77
The HD ring network is an example of a
continuous attractor network (CAN)
78
HD ring network is an example of CAN because... (3)
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
If precise connections are perturbed? (like deleting some HDC cells) in ring of HDC then - (4)
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
Continous attractor def and example (2)
we can place the ball anywhere (our symmetric connections maintain the activity packet in place)
81
Discrete attractor ball def and example (2)
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
Benefits of this HD (4)
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
Problems of HD CAN - (2)
- 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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