Growing Pains in the Brain

1. Growing Pains in the Brain Stuart WG Derbyshire

5. What is the Evidence? Newborn infants have more neurons than they will ever use Those neurons generate high synaptic density in the first 3 years Synapses are then pruned and unused neurons die Critical periods Synaptic pruning is more severe in an impoverished environment

6. We Are Born With More Neurons Than Are �Needed� Between 40 and 75 percent of all neurons born in embryonic and fetal development do not survive They fail to make optimal synapses

8. Unused Neuronal Cell Bodies Die Effect of early closure of one eye on the distribution of cortical neurons driven by stimulation of both eyes. (A) Ocular dominance distribution of single unit recordings from a large number of neurons in the primary visual cortex of normal adult cats. Cells in group 1 were activated exclusively by the contralateral eye, cells in group 7 by the ipsilateral eye. Diagrams below these graphs indicate procedure, and bars indicate duration of deprivation (purple). �Exp�= time when experimental observations were made. (B) Following closure of one eye from 1 week after birth until 2.5 months of age (indicated by the bar underneath the graph), no cells could be activated by the deprived (contralateral) eye. Some cells could not be activated by either eye (NR). Note that the closed eye is opened at the time of the experimental observations, and that the recordings are not restricted to any particular cortical layer. (C) A much longer period of monocular deprivation in an adult cat has little effect on ocular dominance (although overall cortical activity is diminished). In this case, the contralateral eye was closed from 12 to 38 months of age. (A after Hubel and Weisel, 1962; B after Wiesel and Hubel, 1963; C after Hubel and Wiesel, 1970.)Effect of early closure of one eye on the distribution of cortical neurons driven by stimulation of both eyes. (A) Ocular dominance distribution of single unit recordings from a large number of neurons in the primary visual cortex of normal adult cats. Cells in group 1 were activated exclusively by the contralateral eye, cells in group 7 by the ipsilateral eye. Diagrams below these graphs indicate procedure, and bars indicate duration of deprivation (purple). �Exp�= time when experimental observations were made. (B) Following closure of one eye from 1 week after birth until 2.5 months of age (indicated by the bar underneath the graph), no cells could be activated by the deprived (contralateral) eye. Some cells could not be activated by either eye (NR). Note that the closed eye is opened at the time of the experimental observations, and that the recordings are not restricted to any particular cortical layer. (C) A much longer period of monocular deprivation in an adult cat has little effect on ocular dominance (although overall cortical activity is diminished). In this case, the contralateral eye was closed from 12 to 38 months of age. (A after Hubel and Weisel, 1962; B after Wiesel and Hubel, 1963; C after Hubel and Wiesel, 1970.)

9. Critical Periods The consequences of a short period of monocular deprivation at the height of the critical period in the cat. Just 3 days of deprivation in this example (A) produced a significant shift of cortical innervation in favor of the nondeprived eye; 6 days of deprivation (B) produced an almost a compete shift. Bars below each histogram indicate the period of deprivation, as in Figure 24.4. (After Hubel and Wiesel, 1970.) The consequences of a short period of monocular deprivation at the height of the critical period in the cat. Just 3 days of deprivation in this example (A) produced a significant shift of cortical innervation in favor of the nondeprived eye; 6 days of deprivation (B) produced an almost a compete shift. Bars below each histogram indicate the period of deprivation, as in Figure 24.4. (After Hubel and Wiesel, 1970.)

10. Deprivation Causes Brain Structure Changes Terminal arborizations of lateral geniculate nucleus axons in the visual cortex can change rapidly in response to monocular deprivation during the critical period. (A) After only a week of monocular deprivation, axons from the deprived eye have greatly reduced numbers of branches compared with those from the open eye. (B) Deprivation for longer periods does not result in appreciably larger changes. Numbers on the left of each figure indicate cortical layers. (After Antonini and Stryker, 1993.)Terminal arborizations of lateral geniculate nucleus axons in the visual cortex can change rapidly in response to monocular deprivation during the critical period. (A) After only a week of monocular deprivation, axons from the deprived eye have greatly reduced numbers of branches compared with those from the open eye. (B) Deprivation for longer periods does not result in appreciably larger changes. Numbers on the left of each figure indicate cortical layers. (After Antonini and Stryker, 1993.)

11. Deprivation Also has enlarged ventricles and evidence of cortical atrophy.Also has enlarged ventricles and evidence of cortical atrophy.

12. Functional Implications

13. Gesture and Language

14. It�s Not Relevant We cannot extrapolate from the severe to the normal range We shouldn�t �biologise� socioeconomic problems

15. The Science is Theoretically Shallow The model (brain + environment = experience) is wrong What we are extends beyond ourselves, our immediate environment and our individual past because we are social creatures connected through language, tools and a shared history

16. The Brain Is So Over Rated What we �naturally� are is transformed in a myriad of ways and connected to a deep history Nurse Ryan�s embarrassment illustrates this point

17. History Divides Psychology George Herbert Mead Studied under Wundt in Germany �Mentality� is the relationship between the organism and stimuli and is functional rather than substantive Lev Semyonovich Vygotsky Lived through the Russian Revolution Viewed consciousness as the organising feature of mind following his assault on Russian psychology�s focus on reflex and reaction Pavlov, Watson and Skinner The founders of modern behaviourism and the gravediggers of Mead, Vygotsky and their followers Both Mead and Vygotsky recognized that human beings do not merely enter into a world consisting of random elements, bric-a-brac, but they enter into a world of stuff that contain meaning and have symbolic status. Conscious awareness resides in the ability of the organism to indicate to itself the presence of that stuff. In this way, humans are able to control their responses rather than fall into reflexive actions. Vygotsky�s concern with consciousness as the organising feature of mind arose from his assault on Russian psychology�s focus on reflex and reaction and its inability to deal with will or intention except as mystical constructs. Mead and Vygotsky began an effort to draw behaviourism into a more complete formulation of the psychological self. But they were beaten�Both Mead and Vygotsky recognized that human beings do not merely enter into a world consisting of random elements, bric-a-brac, but they enter into a world of stuff that contain meaning and have symbolic status. Conscious awareness resides in the ability of the organism to indicate to itself the presence of that stuff. In this way, humans are able to control their responses rather than fall into reflexive actions. Vygotsky�s concern with consciousness as the organising feature of mind arose from his assault on Russian psychology�s focus on reflex and reaction and its inability to deal with will or intention except as mystical constructs. Mead and Vygotsky began an effort to draw behaviourism into a more complete formulation of the psychological self. But they were beaten�

18. I�m a Mind, Get Me Out of Here

19. Socially Conscious Thought and experience cannot be adequately understood as long as their social origins are obscured You did not, all by yourself, generate the content or momentum of your conscious life The principal idea is that modes of thought and experience cannot be adequately understood as long as their social origins are obscured. All the ideas and sentiments which motivate an individual do not have their origin in him alone, and cannot be adequately explained solely on the basis of his individual life-experience. I imagine that is fairly obvious and uncontroversial when it is directed towards something like our attitudes towards terrorism or our contemplation of meaning but it is clearly more difficult and troublesome when it is directed towards something like the experience of pain. There is a major difficulty in translating across from what can be considered basic sentient experiences and the more complex reflection on those experiences. The principal idea is that modes of thought and experience cannot be adequately understood as long as their social origins are obscured. All the ideas and sentiments which motivate an individual do not have their origin in him alone, and cannot be adequately explained solely on the basis of his individual life-experience. I imagine that is fairly obvious and uncontroversial when it is directed towards something like our attitudes towards terrorism or our contemplation of meaning but it is clearly more difficult and troublesome when it is directed towards something like the experience of pain. There is a major difficulty in translating across from what can be considered basic sentient experiences and the more complex reflection on those experiences.

20. Conclusion We are more than just a brain When deprivation is severe then treating human beings as mechanical objects can make sense But boiling normal development down to mechanics boils out what makes us human