Lecture9 Flashcards
What 2 factors are depended on for maintenance & reorganisation of neural circuits?
Time-dependence (critical & sensitive periods) & Experience/Use (use it or lose it)
In deprivation & enrichment experimental manipulations, what has been discovered when rats are in a deprived environment?;
What about in an enriched environment?;
Which brain region does this occur in?
Fewer synapses & dentritic spines & poor depth & pattern perception;
More dendritic spines & synapses;
Layer 3 of the somatosensory cortex
In enriched environments, what has been found to increase in adult rats?;
What is this associated with?
Neurones in the dendate gyrus of the hippocampus (60% more) & in olfactory bulbs;
Exercise interaction with the enriched environment
What did Bechera & Kelly find about exercise in cognitively enriched rats?;
Exercised & enriched rats were also found to…
It improves object recognition memory & induces brain derived neurotropic factor (mRNA) expression & cell proliferation;
Preferentially explore novel objects
In a study on ocular dominance, when kittens had one eye sutured (leading to monocular deprivation), what was found?;
How did this differ with adult cats?
No cells were activated by the deprived (contralateral) eye - critical period;
There was little effect on ocular dominance but overall cortical activity was diminished (not as catastrophic)
After a week of monocular deprivation in the critical period, what did Antonini & Stryker find was reduced in the deprived eye?;
What about long term deprivation?
Axonal branching in axons from the lateral geniculate nuclei (layer IV in primary visual cortex);
Changes were not comparably greater
What does evidence regarding vision suggest about Competition in neural development?;
What suggests this is not just a single process & that shifting & balancing occurs?
Selective deprivation - ocular dominance columns (layer IV) in many species are developed at birth; deprivation of one eye during sensitive period leads to reduced activation of layer IV of the corresponding visual cortex; That activation of the other cortex by the intact eye increases
What does evidence regarding motor control suggest about Competition in neural development?
In newborns, each muscle cell is innervated by several motor neurons but only 1 survives development; in in-vitro studies, when 1 developing muscle cell is innervated by 2 motor neurons, electrical stimulation (or activation) of 1 neuron, led to degradation of the other
What did Knudsen & Brainard find when they placed prisms over the eyes of barn owls?
Prisms displaced visual field x degrees to the left or right; vision mapping shifted in the direction of the prism; auditory map also shifted in the tectum in the corresponding direction & to the same extent
With the cutting of nerves or sewing together the fingers of one hand, altering demands on the system by increased use, what changes in the somatosensory maps occur?;
What does this suggest about the adult cortex?
The relevant part of the cortex no longer responds to the touch of that finger, but that now defunct area starts to respond to stimulation of the adjacent finger (it fills in the silent area & takes over);
That it is a dynamic area & changes can still happen
What have single unit recordings revealed about individual digit representations in the somatosensory area of monkeys if the 2 fingers of one hand are sewn together?
Months later the cortical map changes so that the sharp border once present between the fingers is now blurred; fingers don’t behave individually anymore
When thumbs & fingers have been stimulated in young string players, what was found?;
What was the size of the effect correlated with?
Responses were higher, suggesting that a larger cortical area is dedicated to touch in musicians;
The age at which they’d begun their musical training (larger responses before 12 yrs)
fMRI scans in adults performing a simple motor task a few minutes each day (touching finger to thumb) showed what?; What does this suggest?
Speed & accuracy improved with practice & greater changes in corresponding motor cortex after a few weeks;
That training can induce rapid changes in brain organisation that reflect plasticity
In Karni et al.’s study, how long did the primary motor cortex show increased activation for in participants who had engaged in training of repeated motor sequences?
Up to 8 weeks, even when no training ensued on the task in the interim
For people with phantom limbs, after time elapses…;
If the amputated part is hurt…;
They still feel it exists & is reduced in size (telescoped); The limb can feel enlarged again
What did Ramachandran find with his patient who had an amputated left arm?;
How can this be explained?
When part of his cheek was stroked, he reported sensations in his missing left hand;
Hand & face representations on the somatosensory map are close together so the face representation can expand & encroach on the hand representation
Where & how does Anterograde neural degeneration occur after brain damage;
From point of disruption forwards to the synaptic terminals (distal segment); happens fast because of separation from metabolic centre
Where & how does Retrograde neural degeneration occur after brain damage?;
What may increase in this case?
From point of disruption backwards to the cell body (proximal segment); happens slow, over days; reduction in size, then death;
Production of proteins (but no guarantee of regeneration)
How does Transneural degeneration occur?
Damage spreads to neurones that are linked synaptically
