locating memories

Question 1

wayfinding

Answer 1

is the set of cognitive processes required to get from here to there

how do we navigate?

Question 2

egocentric

Answer 2

object positions are framed in relation to the self (“I”)

spatial reference frames

Question 3

allocentric

Answer 3

spatial reference frame

object (including self) positions are framed in relation to external objects

absolute: unchanging
intrinsic: depends on orientation of the reference object ie/ right/left

Question 4

categorical wayfinding

Answer 4

technique

qualitative or nominal relationships (general terms)

ie/ above/below, in/on

affect valence biases object spatial memory (good-up; bad-down)

sense of division of things

Question 5

coordinate wayfinding

Answer 5

technique

quantitative or metric relationships (specific)

ie/ 4.67m NW, 3 times this far

Question 6

categorical wayfinding brain area

Answer 6

spatial perception is lateralized to the left cerebral hemisphere

left parietal lesion patients make more categorical errors

Question 7

coordinate wayfinding brain area

Answer 7

spatial perception is lateralized to the right cerebral hemisphere

posterior parietal cortex

right parietal lesion patients make more coordinate errors

actual distances between objects

Question 8

place cells

Answer 8

receive input from many grid cells and code for specific places

located in dentate gyrus

Question 9

grid cells

Answer 9

receive multimodal input and respond to distinct spatial frequencies

located in entorhinal cortex

Question 10

time cells

Answer 10

are sensitive to intervals between key events

located in both dentate gyrus and entorhinal cortex

Question 11

Parts of the hippocampal index theory

Answer 11

Formation
Recognition
Recall
Memory Failure

Question 12

formation

Answer 12

experience is represented in many cortical regions and stored in hippocampus by LTP as an index n

not a memory but a pointer

Question 13

recognition

Answer 13

similar stimuli activate the index, which triggers cortical and subcortical associations of an engram

Question 14

recall

Answer 14

a sufficient subset of stimuli activate enough of the index to then activate the whole index and engram

Question 15

memory failure

Answer 15

insufficient subset of information to reactivate an index

Question 16

episodic memory formation

Answer 16

hippocampus is blind to modality; does not itself discriminate visual, auditory, somatic, olfactory, or other sensory-specific information
- intrinsic theta oscillations (~8Hz), with gamma bursts in each cycle
- the sequence with each gamma burst involves place cells for recently past, current, and upcoming places

one theory proposes that the hippocampus is a general sequence generator for memory
- the “index” is a sequence, not a mere reference to a cell assembly

Question 17

dorsal stream contribution

Answer 17

the dorsal stream supports spatial awareness with three output pathways:

1. Prefrontal Pathway
   - spatial working memory
2. Premotor pathway
   - visually guided action
   - dissociable from purely perceptional or cognitive estimates of distance
3. medial temporal cortex
   - spatial navigation, wayfinding

Question 18

inferior parietal lobule (IPL)

Answer 18

region of association cortex in the right hemisphere specialized for tracking distances

Question 19

what is the rIPL specialized for

Answer 19

spatial distances
temporal distances (intervals)
social distances

parts of rIPL do not discriminate between distance type

Question 20

what are the three egocentric layers of space

Answer 20

personal
peripersonal
extrapersonal

cultural and individual variation exist in average comfortable social distances

Question 21

personal

Answer 21

within ones body

Question 22

peripersonal

Answer 22

within reach

can be adjusted, ue/ when driving

Question 23

extrapersonal

Answer 23

beyond reach

Question 24

where are memories located

Answer 24

episodic memories must encode a location, but the memory itself must also be stored somewhere

engrams are not stored as discrete packets of info in a specific location in the brain

rather, memories are stored as distributed networks of neurons whose connections have been mutually strengthened by encoding and consolidation (everything that contributes to the experience)

Question 25

memory storage: structure of engrams

Answer 25

when an axon of cell A is near enough to excite a cell B and repeatedly or persistently take part in firing it, some growth processes or metabolic change rakes place in one or both cells such that A's efficiency, as one of the cells firing B, is increased cells that fire together wire together

Question 26

techniques for studying engram location have evolved

Answer 26

A. Large cortical ablation B. small cortical ablation C. stereotaxic surgery (BLA) - basolateral amygdala D. stereotaxic surgery

Question 27

how to identify engram neurons?

Answer 27

cell must be active during learning cell must be active during test when activated they can generate the engram behaviour when inhibited they prevent (or reduce) the engram behaviour

Question 28

immediate early genes

Answer 28

genes whose protein products are present after cell activation tagged (co-expressed) with fluorescent protein to measure it problem: it degrades in minutes

Question 29

TetTag mouse

Answer 29

engineered so FOS promotes the expression of Tetracycline-transactivator (ttTA) system tTA promotes reporter gene LAC

Question 30

Detecting Cell Activity

Answer 30

Temporal control over the expression of LAC offers longer tracking of cell activity A. DOX (doxycycline) - inhibits LAC production is an antibiotic that blocks LAC expression when consumed - Remove DOX, LAC is expressed B. Fear conditioning with no DOX causes expression of LAC - add DOX during retrieval - detect coincidence of LAC and ZIF C. LAC and ZIF found more often in cells active in animals who froze more after fear conditioning - sign of both encoding and retrieval

Question 31

Optogenetics

Answer 31

DOX prevents expression of ChR2 (light sensitive receptor) After being fear condition in Context B, mice froze to blue light applied to dentate gyrus in Context A, even on DOX

Question 32

How are engram cells chosen

Answer 32

Experiment: 1. There is a difference between fear retention based on training-test interval A. short intervals (10s) are remembered much less than longer intertrial intervals (8m) B. CREB infusion "restores" fear memory trace for 10s intervals 2. engram cells targeted to die cause the the erasure of the conditioned memory A. CREB can be overexpressed by injecting it into neurons B. CREB overexpression leads to likely selection as engram cell C. Neurotoxin (diptheria) targets and kills cells that overexpress CREB D. Animals that overexpress CREB and treated with diptheria fail to remember

Question 33

How does CREB help a neuron

Answer 33

does it up-regulate genes that are involved in consolidation? - It does but thats not why CREB changes the intrinsic excitability - lowers firing thresholds, making it more likely to join hebbian cell assembly