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.
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