In rat S1, stimulation of connections that stay within a representation (NCB) yields responses that are larger than stimulation of those that cross into an adjacent representation (CB; Hickmott & Merzenich, 1997). Such differences may reflect the fact that there are fewer axons that cross a representational border than project within a representation (Mason et al, SFN Abstr. 2002). In this abstract we investigated whether the synaptic efficacies of NCB connections are larger than those of CB connections. The border between the forepaw and lower jaw representations was mapped in adult rats (>P90) using in vivo recording and marked with DiI. Coronal slices were taken from the marked region and maintained in vitro. Whole-cell recordings were obtained from layer 2/3 neurons close to the border. Horizontal connections within layer 2/3 were electrically stimulated; stimuli were either at a site that was across the border from the neuron (CB) or at an equivalent site within the representation (NCB). The synaptic ...