L1-7 Flashcards
Sensory dermatome refers to
map of areas on the body where sensory info is carried along each of the 31 cranial nerves
describe the 6 layers of the neocortex from outside in
- axons and dendrites, few cell bodies
- densely packed stellate cells, a few small pyramidal cells
- loosely packed stellate cells, intermediate sized pyramidal cells
- bands of densely packed stellate cells, no pyramidal cells
- few loosely packed stellate cells, very large pyramidal cells
- loosely packed stellate cells, pyramidal cells of var sizes
what do Intrinsically Photosensitive Retinal Ganglion Cells (ipRGC) do?
- light senseitive retinal ganglion cells
- most sensitive to blue light
- bottom half of retina (top half of visual field)
- connect through to SCN for entraining circadian rhythms
what is lateral inhibition, in context of shaded rectangles
- excited neurons inhibit surrounding neurons
- opponent process
- darker/less intense surround = less inhibition = perceive as brighter
- for grey rectangle inside white or black background, perceive as lighter against black background
explain opponent process theory of colour vision
- colour vision controlled by activity of 2 opponent systems - blue-yellow and red-green
- Competition between the cones makes the different colours
- adaptation of particular colour receptors favours opponent receptors –> afterimage
simple cells (V1)
- Respond best to elongated bars or edges
- Are orientation selective.
- Have separate ON and OFF subregions
- Can be monocular or binocular (some respond only to one eye, some to info from both
COMPLEX CELLS (V1)
- don’t have off region to the side
- moving in same orientation → still fires
- orientation selective
- Have spatially homogeneous receptive fields (no separate ON/OFF subregions).
- Nearly all binocular.
cortical magnification
lots more of visual cortex devoted to info straight in front, compared to peripheral
Collumnar arcitecture of V1
columns of brain tissue responding to shape in different spatial location - systematically mapped
describe how auditory info gets from ear to cortex
cochlea → brainstem → midbrain (inferior colliculus - own sounds are filtered out here eg breathing, chewing) → medial Geniculate Nucleus of Thalamus - forebrain → auditory cortex
Why tonotopic mapping?
- Reduces axon length? —> Sounds close in frequency are processed together
- Facilitates processing (lateral inhibition)
- Allows sounds to be encoded on the basis of time/frequency changes
- Scene analysis – frequency separation relates to objects in the environment
- lower sounds = big predator
Top down processing in visual vs auditory
Most (66%) connectivity is top down in auditory, compared to ~6% in visual cortex
Why? = language
insert L4 stuff here
Hebb’s model for memory
- cell assemblies/distributed processes
- A unique pattern of activity in millions of cells corresponding to each experience
short term memory (under Hebb’s theory)
circuit feeds back on itself to say active = reverberating
20 sec
long term memory (under Hebb’s theory)
connections would be strengthened so easier to reactivate circuit, needs a cue
recall memory (under Hebb’s theory)
Recall = reactivation of an assembly (network) of neurons, due to different synaptic strength,
- The reactivation is a partial match to the original experience
Strengthening (under Hebb’s theory)
when the postsynaptic and the presynaptic cell fire together → connection between them is strengthened
object perception
= hierarchy of parallel pathways to construct an image
- memory will be stored across these different regions in the brain
object perception - how does info not get confused?
- coordinated TIMING of firing patterns
- Cells firing in synchrony form cell assemblies that collectively represent a given object at a moment in time
- firing at different rates
patient HM
- temporal lobotomy
- severe anterograde amnesia (new mems)
- also retrograde amnesia for 2 years pre surgery
- procedural memory intact
Patient R. B.
- ischemic episode after open heart surgery
- subtle damage in hippocampus
- resulted in selective, marked anterograde amnesia and very minor retrograde amnesia
Patient N.A.
- Damage to the mediodorsal thalamus and mammillary bodies
- connected to hippocampus by fornix
= anterograde amnesia
Wernicke-Korsakoff Syndrome cause and symptoms
- caused by lack of thiamine, due to poor diet
- prevalent in chronic drinker
- impaired memory, paried association, story recall
importance of hippocampus for memory, consolidated and not (explanation for anterograde and retrograde amnesia)
- Without hippocampus → can’t remember because no relay system to link different brain areas
- until consolidated → can remember without needing hippocampus because links established between areas without needing hippocampus
egocentric vs allocentric
- egocentric = things relative to yourself
- allocentric = relative to other things in external world
hippocampus largely allosteric deficit
Hippocampus in london taxi drivers
- anterior hippocampus = smaller
- posterior = bigger
Compared to bus drivers bc bus = repetitive route
Place cells
- cell firing localised to specific location
- each cell represents a different place
- for any location there are some hippocampal cells firing → can be incorporated into memories
- may underlie the ‘where’ of episodic memory
how to test difference between chronological and subjective time
asking how long the task took [time estimation],
or to hold down a button for given time [time production]
time perception with THC, and conclusion
increased time estimation, decreased time production
= perception of time given by neurological condition
chroneostatsis with quick eye movement
chroneostatsis = the stopping of time
- when visual system makes rapid movement (saccade) → surpresses the imput until you refixate again
- nervous system fills in the gap retrospectively → hand of clock seems to sit stationary for a short second
Scalar Expectancy Theory (SET)
- pacemaker/internal clock
- when an event starts → switch on → pulses accumulate → stored in short term memory → compared to memory (specifically the ratio)
what is the ‘pacemaker’?
- a loop of cell activation
- can tag event to this
internal pacemaker is sped up during recall - implications?
Time estimation – duration experienced as longer
Interval reproduction – duration shorter
e.g. THC, life-threatening situation
Ramping
- stimulus getting bigger as you get closer to a reward or something
- This would be observed as individual cells firing during a specific part of an interval
Timing cells in hippocampus
- cells fire after a particular time period
- like place cells but within time
- damage to hippocampus → skewed time recall
- also inability to organise time events
Why do some memories endure?
- we remember what is meaningful, emotional and novel
- emotional content is really important
- e.g. geographically further away from world trade centre = less memory of 9/11 events
adrenaline
- fight or flight
- released from adrenal cortex (hypothalamic–pituitary–adrenal (HPA) axis)
- doesn’t cross the BBB well - influences the brain via activation of the vagus nerve
Cortisol
- HPA axia
- slower stress hormone
