<P> Let us assume that the persistence or repetition of a reverberatory activity (or "trace") tends to induce lasting cellular changes that add to its stability. (...) When an axon of cell A is near enough to excite a cell B and repeatedly or persistently takes part in firing it, some growth process or metabolic change takes place in one or both cells such that A's efficiency, as one of the cells firing B, is increased . </P> <P> The theory is often summarized as "Cells that fire together wire together ." This summary, however, should not be taken too literally . Hebb emphasized that cell A needs to "take part in firing" cell B, and such causality can occur only if cell A fires just before, not at the same time as, cell B . This important aspect of causation in Hebb's work foreshadowed what is now known about spike - timing - dependent plasticity, which requires temporal precedence . </P> <P> The theory attempts to explain associative or Hebbian learning, in which simultaneous activation of cells leads to pronounced increases in synaptic strength between those cells . It also provides a biological basis for errorless learning methods for education and memory rehabilitation . In the study of neural networks in cognitive function, it is often regarded as the neuronal basis of unsupervised learning . </P> <P> Hebbian theory concerns how neurons might connect themselves to become engrams . Hebb's theories on the form and function of cell assemblies can be understood from the following: </P>

Describe hebbian learning as it occurs in the brain
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