Neural and Synaptic Plasticity

To begin with, it is important to keep in mind that the human brain is the most complex organ that we know of. Gerald Edelman (Edelman & Tononi, 2000), Nobel Prize recipient and director of The Neuroscience Institute of Scripps, pointed out that of the 100 billion or so neurons, the cerebral cortex contains about 30 billion and 1 million billion synapses-the possible number of neural circuits is a factor of 10 followed by at least a million zeros. If we counted one synapse per second, we would not finish counting for 32 million years.

The term “neural plasticity” refers to the capacity of the nervous system to exhibit structural and functional adaptations to impinging stimuli. The traditional view of synapses as fixed structures has been replaced by a dynamic one, in which as Smythies (2002) pointed out “Most synapses...are subject to a process of continual pruning, and replacement by new synapses” (p.2). The plasticity of neuronal connections has been studied by subjecting animals to neurosurgical lesions, brain electrostimulation, and a variety of rearing environments. Each of these has yielded morphological and biochemical evidence of synaptic reorganization. Schwartz ( Schwartz & Begley 2002) noted: “The brain’s response to messages from its environment is shaped by experience -- experiences not only during gestation and infancy, as most neuroscientists were prepared to accept, but by our experiences throughout life. The life we live, in other words, shapes the brain we develop” (p.179). Thelen and Corbetta (1994) observed that behavior sculpts brain.

V. S. Ramachandran (ref) has studied various neurological patients, including patients with phantom limb syndrome and somatoparaphrenic delusions. Ramachandran stated:

“The main conclusion to emerge from our experiments...is that we must give up the notion that the human brain is composed of a fixed set of anatomical connections specified largely by the genome. Our results suggest, instead, that even the adult brain is a dynamic biological system in which new connections are being created all the time, partly in response to novel sensory inputs and partly as a result of self-organizing principles...What our results imply...is that even the basic circuitry or hardware in the brain-such as the sensory maps-can be altered with surprising rapidity.”

Brian Koehler PhD
New York University