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Neurological Basis of Behavior (PSY - 610)

Lesson23

DEVELOPMENT OF THE NERVOUS SYSTEM

Objectives:

These lessons would familiarize the students with

· The stages of development of the brain and the changes which takes place

· Various stages of neuronal development.

· Development of the brain: from the fertilization to the various developmental stages in-utero,

and postnatally.

· Cell differtiation, determination, migration, (inside-out), cell competition, Cell death, growth

Cones, Nerve growth Factor and its role, Influences in growth and development of the brain

· Teratogenesis Genetic anomalies which affect development of the brain.

· Plasticity of the Nervous system.

Main Purpose:

This module would take the students through the development and growth (from intrauterine to neonate

stages) to give an understanding of the stages of development and the processes involve.

In the last lesson we discussed some of the influences which can affect normal brain development, we

would continue on the same topic

Oxygen level: oxygen is very important for the brain cells during growth as well as throughout

life. As the embryo depends on the mother for its oxygen supply, any reduction in the normal

level would affect the growing brain. If the mother is not getting enough oxygen during last

trimester, this leads to hypoxia (low oxygen levels) of the fetus. If the mother's blood

circulation is faulty, then it would lead to damage of the brain areas which may have developed

normally, (anemia, and heart disorders in mothers' leads to this problem). This damage is

similar to that of mental retardation. Why? Because neurons die off and lesser number of cells

remains leading to deficient functioning of these areas.

Prenatal motor activity: This is important as there is evidence if there increased activity in

uterus this leads to stronger muscles. This is exercising muscular connection, and their

pathways. Thus motor connections are strengthened even within utero. Not just motor

exercises, but sensory responses are also there. Evidence has shown that the embryo/fetus

responds to mother's lullabies and voice. Those fetuses which are stimulated during the

prenatal period are more alert when they are born.

Drugs: Though the placental barrier protects the embryo, there are some substances which

manage to pass through the protective membranes. It was discovered in the 1960's that drugs

affect the normal growth of the fetus, leading to serious deformities. Thalidomide was the first

drug to have been identified to have teratogenic effects. This sedative was given to expecting

mothers in the 1st three months; it caused major deformities in the growing embryo. Similarly,

morphine, heroin, alcohol, nicotine, cocaine and tobacco also affect the embryo. Mothers are

warned against taking these or other pharmaceutical substances during pregnancy teratogenic

effects

External Stimulation: This is very important for the growing embryo. Unless external

stimulation is received the organs and muscles do not develop normally. Therefore sensory

deprivation leads to irreversible defects in normal growth of the brain. In the now classic

experiments Hubel and Weisel (1963) closed one eye in newborn kitten creating monocular

deprivation. They found monocular response to visual stimuli (only one eye could respond

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Neurological Basis of Behavior (PSY - 610)

even though the visual system was not damaged). In another experiment, kittens were kept in

dark room from birth onwards; it was found that visual pathways atrophy. Similarly, visual

cortical brain areas also degenerate- in this case there is irreversible damage causing blindness.

Thus, early sensorimotor stimulation is important for the brain to grow normally. To stimulate

the brain now some mobile and brightly colored toys are placed in the cots for the newborn to

see.

Complex environment: Rozenwieg et al (1969, 1972) raised rats in an enriched environment

(more toys, swings, ladders, etc). They took out the brains and measured various parts of the

brain. They report a) increased brain weight (especially cerebral cortex), b) increased thickness

of cortical tissue c) larger size of neurons d) more glial cells e) more dendritic spines f)

chemistry of brain also different ( enzyme activity). Greenough (1975) and colleagues also

report that rats raised in a complex environment a) had increased dendritic sprouting b)

responded to novel environment in same way as mildly stimulated rats.

External stimulation environment extremely important but only during the periods in which

it is needed to be present in the system. beyond that neither effect nor repair is possible

References:

1. Kalat J.W (1998) Biological Psychology Brooks/ Cole Publishing

2. Carlson N.R. (2005) Foundations of Physiological Psychology Allyn and Bacon, Boston

3. Pinel, John P.J. (2003) Biopsychology (5th edition) Allyn and Bacon Singapore

4 Bloom F, Nelson and Lazerson (2001), Behavioral Neuroscience: Brain, Mind and Behaviors (3rd

edition) Worth Publishers New York

5. Bridgeman, B (1988) The Biology of Behaviour and Mind. John Wiley and Sons New York

6. Brown,T.S. and Wallace. (1980) P.M Physiological Psychology

Academic Press New York

Note: References 2, 3, 4, and 7 more closely followed in addition to the references cited in the text