The effect of vibrissa deprivation pattern on the form of plasticity induced in rat barrel cortex

Plasticity was induced in the barrel cortex of adolescent rats by depriving every second vibrissa on the contralateral vibrissa pad. This produced a c hessboard pattern of barrels in the cortex where each barrel receiving its principal input from a spared vibrissa was surrounded by barrels for which the principal vibrissa had been deprived and conversely, each barrel receiv ing its principal input from a deprived vibrissa was surrounded by barrels for which the principal vibrissa had been spared. After 7 days' deprivation, responses to the regrown vibrissae were depresse d in layers II/III (49% of control levels) and TV (60%). Depression was far greater than that seen with "all vibrissa" deprivation, suggesting that ac tivity in the spared vibrissae accentuated the depression of the deprived v ibrissae. Depression was not due to subcortical changes as thalamic Ventral Posterior Medial (VPM) responses to deprived vibrissa were unchanged. The short latency responses in layer Iv (5-7 ms) were unaffected by deprivation , but the number of cells responding at intermediate latencies (8-13 ms) wa s markedly reduced (to 66% of control). Potentiation of the spared vibrissa response was substantial in the near side of the neighbouring barrel (2.2- fold increase in layers II/III, 2.9-fold in layer IV) but had not spread to the far side after 7 days' deprivation. Sparing multiple vibrissae may inc rease the rate of potentiation since 7 days is insufficient time for potent iation in single vibrissa spared animals. Potentiation was not due to subco rtical changes as thalamic VPm responses to the spared vibrissa were normal . However, in the spared barrel the response latency decreased by 1-2 ms. O nly the cells responding at short latency exhibited potentiated responses ( 39% increase) suggesting that some thalamocortical plasticity is still poss ible at P28-35. These results show that chessboard pattern deprivation is capable of induci ng substantial plasticity over a wide area of barrel cortex. All the major forms of plasticity seen with other vibrissa deprivation patterns were pres ent, although no other single deprivation pattern studied so far causes the complete repertoire seen with chessboard deprivation.