The role of cortical activity in experience-dependent potentiation and depression of sensory responses in rat barrel cortex

The role of cortical activity in experience-dependent cortical plasticity w as studied in the rat barrel cortex. Plasticity was induced by depriving ev ery other whisker in a chessboard pattern, which is known to cause depressi on of responses to deprived whisker stimulation and potentiation of respons es to spared whisker stimulation. Postsynaptic activity was blocked by musc imol released from elvax slow-release polymer located under the dura and ov er the barrel field. Spared whisker responses potentiated 2.5-fold in layer II/III and 2.9-fold in layer IV of the near-neighbor barrel in animals imp lanted with saline-elvax. In contrast, in whisker-deprived animals implante d with muscimol-elvax, responses were indistinguishable from those in undep rived animals. Similarly, in the spared barrel itself, spared whisker respo nses potentiated 1.3-fold in layer IV in animals implanted with saline-elva x but not at all in muscimol-treated animals. Whiskers that were deprived a nd then allowed to regrow showed depressed responses in saline-elvax-treate d animals, in which 40% of the cells in layer II/III and 26% in layer IV we re unresponsive to their principal whisker. These values fell to 17 and 3% for layers II/III and IV, respectively, in muscimol-treated animals, and th e response magnitude distributions were indistinguishable from undeprived c ases. Cortical activity block had no acute effect on the ventroposteriomedi al nucleus responses and had a transient facilitatory effect after 4 d of m uscimol treatment, which returned to baseline as the muscimol treatment wor e off. We conclude from these studies that cortical activity is required fo r potentiation and depression of sensory responses in barrel cortex.