Plasticity: Changes in Neuronal Connections

Changes in Neuronal Connections

Each day brings us new experiences, and through them we learn new facts, acquire new skills, and gain new perspectives. Our reactions to the world—indeed, our entire personalities—evolve as we acquire knowledge, maturity, and maybe even wisdom. These various changes all correspond to changes in the nervous system, making it clear that the nervous system must somehow be plastic—subject to alteration.

In  fact,  the  nervous  system’s  plasticity  takes  many  different  forms.  Among  other options, individual neurons can alter their “output”—that is, can change the amount of  neurotransmitter they release. On the “input” side, neurons can also change how sensitive they are to neurotransmitters by literally gaining new receptors. Both of these alterations  play  a  pivotal  role  in  learning,  and  we’ll  return  to  these  mechanisms.

Neurons  can also create entirely  new connections, producing new synapse in response to new patterns of stimulation. The changes in this case seem to take place largely on the dendrites of postsynaptic cells. The dendrites grow ne dendritic spines—little knobs attached to the surface of the dendrites (Figure 3.38; Kolb, Gibb, & Robinson, 2003; Moser, 1999; Woolf, 1998). These spines are the “receiving stations” for  most  synapses; so  growing  more  spines  almost  certainly  means  that, as  learning proceeds, the neuron is gaining new synapses—new points of communication with its cellular neighbors.