E Guic-Robles | PubMed Health

PubMed1992

Vibrissal roughness discrimination is barrelcortex-dependent.

We have investigated the contribution of the neocortical vibrissal representation within the posterior medial barrel subfield (PMBSF) to the high performance levels obtained by rats in a complex roughness discrimination task mediated by vibrissal inputs. Nine binocularly occluded rats were trained in a two-choice roughness discrimination until they obtained the 85% correct response criteria. Subsequently, the PMBSF was localized by electrophysiological recordings and bilaterally ablated. The locus and extent of the cortical lesions were confirmed by histological analysis after additional training and testing. There was no evidence of task retention after the cortical lesion and barrelless rats were unable to obtain prelesion discriminative performance levels when stimulation was restricted solely to vibrissal cues. After extensive postlesion training, four of these rats were allowed to palpate the discriminanda with their forepaws. Under these conditions rats rapidly reached the 85% correct criterion once again. The present results indicate that the PMBSF is essential for complex tactile discrimination when sensory information is obtained through the vibrissae by active palpation. This deficit is specific for the vibrissal system, the PMBSF is not essential to solve the same tactile discrimination task when the source of the somatosensory information is provided by other non-vibrissal cutaneous sensory receptors.

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PubMed1987

Rats with lesions in anteromedial extrastriate cortex fail to learn a visuosomatic conditional response.

The involvement of rat anteromedial extrastriate cortex (area AM, in the anterior portion of area 18b) in the integration of visual and somatic cues was assessed behaviorally. Following restricted bilateral lesions of selected cortical regions, rats were tested on their ability to retain or relearn a conditional visuosomatic discrimination task learned prior to surgery. Two compound, visuosomatic stimuli were used: white or black associated with either one of two degrees of roughness. The use of a guided-response procedure was essential for rats to learn this difficult conditional bimodal task. None of the 6 rats with lesions aimed at area AM retained the habit postoperatively. Four of these rats were incapable of relearning the task after 3 postoperative training series, and they had either extensive lesions of area AM or relatively small, symmetric damage of anterior portions of AM. The remaining two rats with lesions in area AM were able to relearn the task in the second postoperative training series, and their lesions either were restricted to posteromedial aspects of area AM or they involved asymmetric loci in anterior area AM. In contrast to rats with lesions of area AM, rats with lesions in visual cortex in areas 17 and 18a, or in auditory cortex in area 41, were able either to retain the task or to relearn in the first postoperative training series. These results indicate that the integrity of area AM appears necessary for rats to discriminate between pairs of compound stimuli that differ in brightness and roughness. The behavioural data point to the notion that this area might be involved in the integration of these types of visual and somatic stimuli. In addition, our finding that performance was largely unimpaired following extensive lesions of lateral extrastriate area supports previous reports indicating that medial and lateral extrastriate visual areas differ in function.

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