Visual behaviour mediated by retinal projections directed to the auditory pathway

An unresolved issue in cortical development concerns the relative contribut ions of intrinsic and extrinsic factors to the functional specification of different cortical areas(1-4). Ferrets in which retinal projections are red irected neonatally to the auditory thalamus(5) have visually responsive cel ls in auditory thalamus and cortex, form a retinotopic map in auditory cort ex and have visual receptive field properties in auditory cortex that are t ypical of cells in visual cortex(5-8.) Here we report that this cross-modal projection and its representation in auditory cortex can mediate visual be haviour. When light stimuli are presented in the portion of the visual fiel d that is 'seen' only by this projection, 'rewired' ferrets respond as thou gh they perceive the stimuli to be visual rather than auditory. Thus the pe rceptual modality of a neocortical region is instructed to a significant ex tent by its extrinsic inputs. In addition, gratings of different spatial fr equencies can be discriminated by the rewired pathway, although the grating acuity is lower than that of the normal visual pathway.