Critical periods Flashcards
Outline Harlow’s experiments and identify their significance.
Experiment in 50s- effect of early maternal deprivation on subsequent social and cognitive behaviour in monkeys. Deprived monkeys of their parents after they were born and observed the effect that they had on their subsequent life. Abnormal life, esp social interactions, were timid, did not explore, became bad parents and passed on this inability to their children (intergenerational affect). One of the main faceats was also the consideration of tactile communication.
What did MRI tractography reveal in regards to the connections in the prefrontal cortex
Abnormally sparse connections in the prefrontal cortex (particularly the ventral medial prefrontal cortex) which is all about social conditions (Social learning, social mileu, social cognition)
Describe the phenomenon of “learnt present” in relation to critical periods
Learnt present essentially means that you are present in the moment but it requires to you to remember how you learned it. What this means is that with critical periods for normal social behaviour it is not seen when the behaviours are taught or modelled or even seen- but they are still required then.
Describe the experiments that were done in relation to critical periods in the visual system
Radioactive amino acids are injected in the eye– transynaptic transport at the retinal ganglion cells- travels to the LGN of the thalamus and terminates in layer 4 of the visual cortex. these terminate as bright visible bands on the autoradiogram.
Kitten experiments
Light shined no closure you get this cortical reading from all cells, closed for 2.5 months from beginning- just got input from the ipsilateral open eye with some not responsive. Close after first 12 mths of light yes cortical activity is diminished but still had bell curve not NR. Close eyes for 3 days in the critical period skew, 6 days almost exclusively ipsilateral
What are the effects of monocular deprivation of the LGN axons in the visual cortex
After a week of monocular deprivation during the critical period, axons terminating on layer 4 in the PVC from LGN neurons have greatly reduced numbers of branches compared with that of the open eye. Deprivation of longer periods does not result in appreciably larger changes in the arborization of the geniculate axons.
What is meant by competitive interaction between eyes?
In monocular deprivation the active eye gains a competitive advantage and replaces many of the synaptic inputs from the close eye. Despite the LGN being retained in the cortex few if any neurons fire AP when light is presented in the deprived eye.
Describe the impact of strabismus (lazy eye)
Objects within the same location in the visual space can no longer stimulate corresponding points on the 2 retinas at the same time. The overall activity of the eye remains the same but you get a decrease in the number of binocualrly driven cells namely (3,4,5) and as a result most responses are driven exclusively by one eye or another. Must have surgery by the age of 6-7
What does the amygdala have to do with critical periods? Is it significant?
We know that the amygdala activates something upstream that makes use feel afraid probably the cingulate cortex- and activates downstream system in response to fear it also activates endocrine changes through the activation of the HPA axis that will ultimately result in the release of cortiosl. The critical period is when this circulatory develops, links between the prefrontal cortex, hypothalamus and amgydala and other aspects of autonomic function. The capacity to feel drives our social cognition- if that does not wire corrrectly than it never does.
Describe the improvished and maltreated child effect in terms of the HPA axis and calcium.
Hippocampal neurons during vulnerable periods may be overexcited by cortisol- you can get a death or neurons. We know Ca is an important bioregulator that is present in low concentations. Usually mitochondrion sequester Ca and put into the SER. If vulnerable lots of NMDA because of LTP- you get overexcitation and death of the cells and you remove the break on this pathway- positive feedback and get extra cortisol that adds to the neurotoxicity.
