Gabaergic inhibition antagonizes adaptive adjustment of the owl's auditory space map during the initial phase of plasticity.

We studied the influence of GABA-mediated inhibition on adaptive adjustment of the owl's auditory space map during the initial phase of plasticity. Plasticity of the auditory space map was induced by subjecting owls to a chronic prismatic displacement of the visual field. In the initial stages of plasticity, inhibition suppressed responses to behaviorally appropriate, newly functional excitatory inputs. As a result, adaptive changes in excitatory input were only partially expressed as postsynaptic spike activity. This masking effect of inhibition on map plasticity did not depend on the activity of NMDA receptors at the synapses that supported the newly learned responses. On the basis of these results, we propose that the pattern of feedforward inhibition is less dynamic than the pattern of feedforward excitation at the site of plasticity. As a result, initially in the adjustment process the preexisting pattern of feedforward GABAergic inhibition opposes changes in the auditory space map and tends to preserve the established response properties of the network. The implications of this novel role of inhibition for the functional plasticity of the brain are discussed.