A remarkable demonstration of experience-dependent learning was seen in the experiment of Sur, Garraghty and Roe (1988). The experimenters redirected the visual inputs to the auditory cortex and vice versa and came across a path breaking finding. The neurons of the auditory cortex developed properties of the visual receptive field. However, the reverse did not happen. The visual cortex did not show properties of the auditory cortex. Although this experiment was conducted on rats, it does reflect how neural plasticity can make one learn from the experience. As far as human beings are concerned, their brain is extremely plastic in nature and learns from experiences. We have already discussed neural plasticity in the first unit.

Let us now talk specifically about human beings. It has been found that with age neurons become more myelinated along with thickening of the axons and increase in the number of synaptic boutons. The myelination of neurons by oligodendrocytes from 5-18 years influences the size of the brain (Giedd et al., 1996). The neurons of the corpus callosum show remarkable increase in myelination between 6 months to 3 years, which further continues (Paus et al., 2001; Thompson et al., 2000). Myelinated axons are supposed to facilitate learning mechanism. As life conditions might be different for different people, age is not the only determinant. Studies of human children having experienced neglect suggest delayed head growth and cognitive development. As a consequence their academic achievement in adulthood gets adversely affected. R esearch on hemispheric specialization and cognitive development suggest that the specialization of the two halves of the brain takes place at a very early stage. Atypical cognitive development could be due to damage to the cerebrum or because of the combined effect of cerebral damage and maladaptive activation pattern of the subcortical activating system.

Neuropsychological studies have confirmed that the d amage to the medial temporal lobe including the hippocampus severely affects learning. Hippocampal lesions in human beings also impair episodic memory. In terms of rate of learning, the hippocampal system learns fast whereas t he cortical system learns slowly but incrementally. On the basis of their study of context specificity of conditioning Good and Honey (1991) have shown the involvement of hippocampal-formation in incidental learning.

As human beings we learn from our experiences and the memory of such events helps us not commit the same errors that were committed earlier. Much such learning is stored in our memory. Interestingly, memories stored by the hippocampus have been found to be flexible. This means that one can infer from it in novel situations; and this makes us human.