VISUAL PROJECTIONS INDUCED INTO THE AUDITORY PATHWAY OF FERRETS .2. CORTICOCORTICAL CONNECTIONS OF PRIMARY AUDITORY-CORTEX

Although the development of corticocortical projections has been well studied, less is known about the role of sensory inputs in the specifi cation of these connections. As part of an ongoing series of studies i n our laboratory, we have examined the role of thalamic input modality in the development of corticocortical connections. These studies invo lve making unilateral lesions and inducing retinal inputs into the aud itory thalamus (MGN) during early development in ferrets, thereby conf erring visual responsiveness on primary auditory cortex (AI). In this way we can examine the role of input identity in cortical specificatio n in general, and connectivity patterns specifically. A previous paper (Pallas et al. [1990] J. Comp. Neurol. 298:50-68) described the patte rn of thalamocortical and corticothalamic connections of auditory cort ex in normal and lesioned animals. This study compares the pattern of auditory corticocortical connections in normal and lesioned animals. W e injected neuroanatomical tracers into AI and mapped out the distribu tion of retrogradely labelled cells in the cortex. We report that the cortical inputs to ferret Al resembled those in cats, and that the pat tern of ipsi- and contralateral corticocortical connections of ferret AI with visual input was similar to the normal.pattern. Auditory corte x with visual input did not make ectopic connections with visual corte x, but maintained its connections with other auditory cortical areas. These results suggest that the overall corticocortical connections of an area are not influenced by the modality or activity pattern of its inputs. In particular, altering the input activity to a cortical area does not seem to promote the formation of entirely new connections, al though small changes in the strength of existing connections are possi ble (Sur et al. [1990] Trends Neurosci. 13:227-233). (C) 1993 Wiley-Li ss, inc.