Somatic sensory cortical regions of the agouti, Dasyprocta aguti

The localization and organization of primary (SmI) and secondary (SmI) somatic sensory cortical regions in agoutis, have been studied with micro- and macroelectrode-evoked potential techniques. For SmI, the mean surface area determined using microelectrodes was 13% smaller than that obtained using macroelectrodes. The location and organization of SmI are similar to those of other rodents: the largest representations were those of the vibrissae, the perioral regions and the first digit of the hand. As in some other animals, SmII is related to both sides of the body. It shows excellent somatopic differentiation and was located lateral and posterior to SmI, in relation to which it is arranged as a reduced mirror image. The area of SmII represents 31% of that of SmI in agoutis. The large size of the forepaw representation in SmI is reflected in SmII, that of the face representation is not; this agrees with similar findings from several other species. SmI was completely mapped using light touch stimuli, and contains many projections from vibrissae and hairs along with some proprioceptive projections. SmI overlaps with visual projections. SmII receives less light touch, vibrissae and hair projections than SmI, and it receives numerous deep mechanical and auditory projections. In SmII latencies were 10.96 msec for somesthetic and 13.39 msec for auditory stimuli; in SmI latencies were 13.25 msec for somesthetic and 39.80 msec for visual stimuli. One sulcus separates the SmI projections of the forelimb from those of the hindlimb, and another is often found marking the posterolateral boundary of SmII.