cortical maps and plasticity

Question 1

Maps in the brain

Answer 1

The barrel cortex - somatosensory cortex
area of brain in rodents where representations of their whiskers are mapped out.
The basic spatial relationship of their whiskers are mapped out in their brains with co-ordinating cells.

INFO about world is transmitted to the brain through the stimulation of whiskers
the barrel cortex is this map

Question 2

These maps are also involved in the visual system

Answer 2

“space” is mapped similarly
This mapping connects a location on the retina with groups of neurons within the lateral geniculate nucleus and the primary visual cortex
However the maps do not reflect the size of space- but the density of receptors in that area
retinotopic map

Question 3

NOt only location

Answer 3

code for orientation - certain cells sensitive to specific orientations
One neuron fires the most for verticle lines - however never stops firing completely
when we combine these neurons we get an orientation selective map

Question 4

Testing this theory

Answer 4

neurons in cortical maps have RECEPTIVE FIELDS
the RECEPTIVE FEILD of a neuron is of ‘feature space’ that it responds to strongest (fires most action potentials to)
can be a LOCATION (a whisker or a finger) or an orientation.
same acrosss species

Question 5

Across species

Answer 5

Although this basic mapping can be applied to all species there are small variations relative to the animals enviroment and behavior.
For example in the blind mole rat a much larger portion of the mapping is represented by its body

Could individual differences in the mapping of cells also reflect inter-species individual differences

Question 6

Plasticity

Answer 6

William James first suggested organic matter has some kind of plasticity

Not all experiences are equal - Lorenz studied effects of early life on the behaviour of gees.
Hypothesised that as they hatch and see their mother this encodes behaviour so that they stay close to the mother.
found that when the first thing they sam was him- they would follow him
this highlights that there is a critical period in which crucial stimuli can greatly influence behavior in later life

Question 7

Critical period in humans

Answer 7

• can be seen through research an bilingualism. To be fluent in a second language like that of a native you must learn before aged 12

Question 8

Environmental exposure during critical periods can drive cortical map development

Answer 8

• kittens were raised in impoverished visual enviroments (couldnt see own body)
  could only see either vertical or horizontal lines
  -Orienation cells within the visual cortex were not tuned for orientations that the kittens werent exposed to

Question 9

exposure beyond critical period

Answer 9

• post critical period we can still learn (plasticity)

Question 10

mechanoreceptors

Answer 10

• have ability to turn touch into codes the brain can understand
  (cutaneous sensitivity) - information from skin
  -skin largest organ- thickness varies .5mm to 4mm 16% of bodyweight

cutaneous somatosensory receptors (skin receptors)

Question 11

Ascending pathways - the dorsal column

Answer 11

Pathway to touch

- fingertips have much of the cortex representing because they are densley packed with receptors

Question 12

Plasticity in the primary somatosensory system

Answer 12

• first work to demonstrate two topographic representations of the body in the brain of monkeys
  areas 3b and 31 mirror eachother (static map)

-amputate finger of primate to see what would happen to the map of the hand
does not create silent zone - responds to surrounding touch

-then induced experimental syndactyly (joined two fingers together) which resulted in more temporally-coincident input to the two digits- which corrilated with the boarders between the two receptors becoming less distinct = dual digit rfs