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PHGY314 > Hippocampus > Flashcards

Hippocampus Flashcards

1
Q

where was patient HM’s lesion that caused his epilepsy?

A

behind frontal lobe

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2
Q

what type of memory was affected in HM?

A

declarative / episodic memories

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3
Q

what is declarative/explicit memory?

A

events (episodic memory) and facts (semantic memory)

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4
Q

what is nondeclarative/implicit memory?

A

procedural memory, perceptual representation, classical conditioning, nonassociative learning

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5
Q

what does CA stand for?

A

Cornu amonis

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6
Q

what contains the hippocampal formation?

A

CA1-3, dentate gyrus, entorhinal cortex, subiculum, pre and Para-subiculum

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7
Q

what is the human hippocampus volume compared to rat and monkey?

A

human hippo volume is 100x bigger than a rat’s and 10x bigger than a monkey’s

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8
Q

what type of cells are in the dentate gyrus and CA1/3 and how many?

A
  • DG = 1.2 million GRANULE cells, 4000 basket cells, 32 000 hilar interneurons
  • CA3/1 = 330 000 to 420 000 PYRAMIDAL cells, many interneurons too
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9
Q

what layers of the entorhinal cortex project where?

A
  • layer II = DG and CA3
  • layer III = CA1 and subiculum
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10
Q

what layer of EC receives input from what region of the hippo?

A

EC layer 5 receives from CA1 and subiculum

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11
Q

what synapse is one of the largest and most powerful in the brain?

A

the mossy fiber synapse!

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12
Q

what type of connections are between DG and CA3 and CA1?

A

DG -> mossy fibers -> CA3 -> schaffer collaterals -> CA1

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13
Q

what are the 3 inputs going to CA3? how many of each?

A
  1. 50-80 mossy fibers from DG
  2. 3 500 perforant pathway from EC layer 2
  3. 12 000 recurrent collaterals from CA3
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14
Q

the recurrent collaterals in CA3 are separated between what?

A

they either go to basilar dendrites (8000) or to apical dendrites (4000)

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15
Q

where does CA1 get input from?

A
  • schaffer collaterals from CA3
  • from EC layer 3
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16
Q

where does the medial vs lateral EC projections separate and where do they each go to?

A

medial EC layer 3 go to proximal CA1, lateral EC layer 3 go to distal CA1

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17
Q

what is the hillus reciprocally connected to?

A

to the DG

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18
Q

what does inactivation of the medial septum do in rodents? how was it tested?

A

impairs memory! rats can’t remember where the platform is in the water maze anymore

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19
Q

what type of memory is encoded in the hippocampus?

A

episodic memory (type of declarative memory)

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20
Q

what kind of hippo lesions disrupt memory performance in the water maze?

A

mostly dorsal lesions

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21
Q

how did they test for how long it takes for memory to move from the hippo to the cortex?

A
  • they shock a rat at the same time as a tone: rat associates tone with shock
  • they lesion the hippo after 1, 7, 14 or 28 days
  • then test if the rat freezes when it hears the tone to see if it remembers the tone-shock association
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22
Q

what were the results of the tone-shock pairing and hippo lesions experiment? what can we conclude?

A

when lesioning the hippo after 28 days, the rat remembers the tone-shock pairing (freezes when hearing the tone), meaning the memory moved to the cortex

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23
Q

what do you call memory that moved from hippo to the cortex?

A

semantic memory

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24
Q

what is high pass filtering used for in extracellular recordings?

A

filter out the frequencies below 800Hz (local field potential) to look at higher frequencies only (spikes)

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25
Q

where are neurons that encode the location of the animal located?

A

in the medial temporal lobe

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26
Q

name the 3 types of neurons that encoded animal’s location

A

grid cells, head direction cells, place cells

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27
Q

what hippocampal neurons fire everywhere (at any location)?

A

interneurons are not place specific

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28
Q

what happens when rat’s medial forebrain bundle MFB stimulation is paired to a specific place cell during rat’s sleep?

A

the rate run’s to the location encoded by the place cell!

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29
Q

head direction cells have been recorded in rat pups as of when?

A

3-4 days before they open their eyes

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30
Q

what part of the brain had head direction, place and grid cells?

A

entorhinal cortex

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31
Q

what type of location cells are found in the hippocampus?

A

only place cells

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32
Q

what are angular velocity cells?

A

cells that fire when the animal turn its head in a specific direction

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33
Q

head direction cells can be tuned to what?

A

clock wise vs counter clockwise

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34
Q

where are head direction cells found?

A
  • lateral mammillary nucleus
  • anterior dorsal thalamic nucleus
  • postsubiculum
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35
Q

how is the tuning curve of head direction cells in the lateral mammillary nucleus vs the anterior dorsal thalamic nucleus?

A
  • lateral mammillary nucleus = wide tuning curve
  • anteriodorsal thalamic nucleus = narrow tuning
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36
Q

what is the difference between ADN (anterior dorsal thalamic nucleus) and PSC (postsubiculum) head direction cells?

A

ADN HD cells fire before the stimulus and anticipate the head movement.
PSC neurons fire when the head actually turns

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37
Q

ADN head direction depend on what? how did they test this

A

on vestibular inputs;
they induced vestibular system lesions with sodium arsanilate in the inner ear and it decreased the firing rate of ADN HD cells

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38
Q

what other brain area was lesioned to test the role of vestibular input on ADN HD cells?

A

dorsal tegmental nucleus, the last part of the vestibular circuit

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39
Q

what were the results of dorsal tegmental nucleus lesions on ADN HD cells firing?

A

caused least fine tuning for head direction

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40
Q

what did lesions to the lateral mammillary nucleus do to ADN HD cells?

A

almost completely decreased the firing of head direction cells

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41
Q

HD cells in what region required input from ADN? how did they find that?

A

postsubiculum; ADN partial lesion leads to big widening of presubiculum HD cells tuning curve

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42
Q

what brain area that connects to ADN is not necessary for ADN HD cells function?

A

postsubiculum (postsubiculum lesions don’t affect ADN firing)

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43
Q

so far the data suggests that an interaction between what brain areas is critical for generating HD cell signal?

A

DTN (dorsal tegmental nucleus) and LMN (lateral mammillary nucleus)

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44
Q

they recorded ADN HD cells activity and found that it correlated with what?

A

with the error the rat made finding its way back in the dark

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45
Q

ADN HD cell firing corresponding with heading erros means that HD cells act as what?

A

internal compass

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46
Q

what happened to HD cells (i assume ADN HD cells) when rat went upside down? what does that mean?

A

no more firing; rats don’t have HD cells for upside down

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47
Q

what are the 3 models used to explain 3D encoding of HD in bats?

A
  • pure azimuth cell: only fire when looking in a quadrent
  • pure pitch cell: only fire when looking down
  • azimuth and pitch cell mix
48
Q

what cells are active during sleep?

A

ADN HD cells

49
Q

how do ADN HD cells fire during sleep?

A

in cycles, going around the 360°

50
Q

almost all cell in hippocampus are?

A

place cells

51
Q

how did expanding the environment affect place field cells?

A

the firing field of place cells expanded with the environment

52
Q

the taxi driver human computer game showed evidence for the presence of what type of cells in humans?

A

hippocampal place cells

53
Q

how did they test for rodents encoding of 3D space?

A
  • cage experiment, making them go upside down
  • staircase experiment
54
Q

do rodents place cells code for 3D?

A

no (place cells were firing at almost every level of the staircase)

55
Q

what are attractor states?

A

pattern completion (assuming a pattern with little info)
pattern separation (seeing the 2 possible patterns)

56
Q

what information allows us to fall into pattern separation?

A

having a big change in input (higher difference between 2 images)

57
Q

‘Remapping’ of hippocampal place cells between contexts: what is global remapping?

A

when presented to 2 identical rooms, the hippocampus creates 2 separate maps in which the same neuron will fire at different location

58
Q

‘Remapping’ of hippocampal place cells between contexts: what is rate remapping?

A

when presented twice to the same room in which things have changed, the hippocampus change the rate of fire; the same neuron fires at the same location but at different intensities in each room

59
Q

in what context does global vs rate remapping happen?

A
  • small change of input between 2 environments = rate remapping
  • big change in input = global remapping
60
Q

what happened to animal’s place cells when they were put in different rooms that slowly changed from square to circle

A

the place cells fire normally until the animal realises its a new room, global remapping happens (clear cut)

61
Q

why do place cells do rate remapping?

A

to signal memory

62
Q

how was rate remapping showed in an experiment?

A

asking an animal to turn left or right: some place cells fired more when turning right or left

63
Q

what part of the hippo generates place cells?

A

CA1; it generates the spatial map

64
Q

how did CPP (NMDA receptor blocker that blocks LTP) affect place cells?

A

it abolished long-term stability of newly formed place cells (can make new place fields but can’t retain the info)

65
Q

what did they find when looking at the entorhinal cortex for place field signal?

A

nothing

66
Q

what happened when they cut the connection from CA3 to CA1? what can we conclude?

A

place cells were not affected, therefore place cells originate after CA1 (in CA3)

67
Q

what happens in the water maze if you lesion LEA (lateral entorhinal cortex)?

A

the animal perfroms well in the water maze. no effect

68
Q

what happens in the water maze if you lesion MEA (medial entorhinal cortex)?

A

the animal struggles in the water maze (place cells are affected)

69
Q

after realizing that MEA lesions affect water maze experiment, they recorded MEA. what did they find?

A

beautiful place fields

70
Q

where in MEA did they find place fields?

A

dorsal MEA

71
Q

MEA recording found that each neuron had..?

A

multiple place fields

72
Q

what about ventral MEC? (MEA = MEC)

A

neurons there had weak spatial tuning, unlike dorsal

73
Q

what pattern of activity was found in MEC place field when the animal was put in a large environment?

A

hexagonal grid of fields; equilateral triangles between place field; from that came grid cells

74
Q

what happened to the grid cells in MEC in the dark?

A

their place fields persist! must be keeping track of the animal’s movement

75
Q

what is one different between grid cells and place cells?

A

grid cells will always be grid cells no matter if the environment changes. Place cells change depending on the environment.

76
Q

when do grid cells form?

A

they immediately start forming a grid field when entering a new environment

77
Q

when did they find the most activity in grid cells/entorhinal cortex?

A

when an animal OR HOMUAN moves at a 60° angle, in line with the lines of the grid field

78
Q

how does speed affect the activity of human’s entorhinal cortex?

A

faster speed = more activity

79
Q

what occurs at the same time as global remapping of place cells?

A

realignment / remapping of grid cells / shift of grid field

80
Q

they made the rats run in an 18m long tunnel and found what when measuring the activity of MEC?

A

dorsal MEC had more and smaller place fields,
ventral MEC had less but bigger place fields

81
Q

they did the same experiment in the hippocampus. what did they find?

A

progressive increase in place cells from dorsal to ventral hippocampus (place fields get way bigger in ventral hippo)

82
Q

this link in entorhinal and hippocampus grid / place fields widening led to what conclusion?

A

grid cells drive hippocampal place fields

83
Q

what happened to GRID CELLS in a multi-compartmental environment?

A

grid fields code each hallway as if it was the same… they don’t make triangles patterns anymore

84
Q

what happened to PLACE CELLS in a multi-compartmental environment? (hippo)

A

they also code for each hallway independantly, not forming a pattern (re-listen some of that class cus what)

85
Q

the fact that hippo place cells and entorhinal cortex grid cells respond the same way to a multi-compartmental environment proves what?

A

that the place field signal in hippocampus comes from the entorhinal cortex!

86
Q

multiple grid cells with the same what project to one place cell?

A

they have the same center (a place field in the middle)

87
Q

what other brain area acts like the hippocampus? (lesions has the same behavioral effects)

A

medial septum

88
Q

more precisely what do lesions / inactivation of the medial septum do?

A
  1. they eliminate theta oscillations throughout the medial temporal lobe
  2. disrupt the triangle pattern of GRID cells
89
Q

what drug did they use for medial septum inactivation?

A

mucimol

90
Q

how did they test the model of grid cells projecting to place cells?

A

via septum inactivation, to see if it stops grid AND place fields

91
Q

what did they find about place field when inactivating the medial septum? what does this mean?

A

animals can still form place fields! meaning that grid cells are not necessary for place cells :o

92
Q

what are conjunctive cells?

A

grid cells that are also sensitive to head direction

93
Q

what are boundary vector cells?

A

cells that fire in bands across the environment determined by the distance of the animal from a boundary in a certain direction

94
Q

where are boundary vector cells and conjunctive cells found?

A

MEA medial entorhinal cortex

95
Q

what is the now the model for place cells after boundary vector cells discovery?

A

boundary vector cells combine to make place cells

96
Q

apart from grid cells, head direction cells, conjunctive cells, and boundary vector cells, what other localization cell type is found in the MEC?

A

speed cells

97
Q

apart from place cells, what other memory-related cells are found in the hippocampus?

A

time cells (signal for WHEN)

98
Q

why does it make sense for episodic memory to be located in the hippocampus?

A

because the main component of episodic memory is the context, including the environment (where) and timing (WHEN)

99
Q

how did they find the MEC speed cells?

A

by letting rats run on treadmills and noticing that the firing rate of some MEC neurons followed the speed even when running sur place

100
Q

how did they test for hippocampal time cells?

A

they made rats run on a treadmill in a delay zone and found cells that fired depending on how long the animal was running in the box

101
Q

are time cells only in the hippocampus?

A

no ish… grid cells in EC also code for distance and time on a treadmill (animal isn’t actually moving)

102
Q

give the characteristics of hippocampal theta oscillations

A
  • 6-10 Hz oscillation in local field potential in hippocampus and related structures
  • observed during exploration and attentive behaviors in rats, mive, bats, pigeon, monkeys, humans
  • highly precise spike timing throughout the hippocampal structures
103
Q

what is theta phase precession?

A

place cell has rhythmic firing that slightly precedes the theta oscillations because it oscillates faster than the extracellular recording of theta oscillation

104
Q

when does the place field fire in the middle of a theta oscillation in phase precession?

A

when the animal is in the middle of the place field

105
Q

where is phase precession observed in the brain?

A

in entorhinal layer II grid cells but not in layer III grid cells

106
Q

how did they prove that the oscillations of the place cells come from the place cells themselves?

A

single cell recordings of entorinal layer II

107
Q

what is the consequence of phase precession? explain

A

precise temporally structured call assemblies: in one theta cycle, you have info about where you are coming from and where you are going

108
Q

how does the firing of the neuron changeswhen it enters its place field?

A

it goes from firing at 8Hz to firing at 9Hz when we enter the cell’s place field

109
Q

what happens when the animal is still and sleep?

A

hippocampus stops firing in theta state and fires in short wave ripples + sharp waves

110
Q

during what kind of sleep do sharpwave ripples occur?

A

slow wave sleep

111
Q

what happens to place cells during sharpwave ripples?

A

place cells (pyramidal cells) reactivate! in the order that they were activated during the movement

112
Q

why do we have sharpwave ripples in the brain?

A

hippocampus sequences out (replays) displacements when we are not moving to remember it and to send it to the cortex

113
Q

researchers can estimate the animal’s location based on what?

A

on its place cell firing

114
Q

sharpwave ripples trigger activity where in the brain?

A

in all of the cortex :o how info gets from hippo to the cortex?

115
Q

they blocked the hippocampus when sharpwave ripples are about to happen and found what?

A

Blocking hippocampal sharpwave ripples impairs memory consolidation

PHGY314 (9 decks)

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