Synaptic plasticity and the organization of behaviour after early and latebrain injury

Hebb proposed that synaptic change underlies behavioural and cognitive plas ticity. When applied to recovery from brain injury, the general hypothesis is that if there is recovery following brain injury, then there ought to be a correlated synaptic change, which is presumed to be responsible for reco very. In contrast, if recovery fails to occur, or expected recovery is bloc ked in some manner, then the synaptic change will likely nor be present. Sy stematic study of functional recovery and synaptic change following brain i njury at different ages supports these predictions. Good recovery is always correlated with enhanced connectivity whereas poor recovery is always corr elated with an absence of reorganized connectivity. Furthermore, factors th at stimulate recovery, such as neurotrophins or experience, stimulate synap tic change and functional recovery. Factors that retard recovery, such as d epletion of neuromodulators, also block synaptic change. These results thus support Hebb's general idea that synaptic plasticity is related to behavio ural change.