Gustatory deficits produced by lesions of the thalamic taste nucleus

Rats were trained preoperatively to detect 0.8% NaCl using an operant conditioning procedure in which the tastant served as the discriminative cue for reinforcement. Bilateral lesions were made in the parvicellular portion of the ventral posteromedial nucleus (VPMpc) in four rats and just posterior to the VPMpc in three rats. Control rats received sham lesions (n = 5) or lesions dorsal to the VPMpc (n = 4). Postoperatively the sham controls demonstrated excellent retention of the detection task. Rats with lesions outside of the area of the taste nucleus had no deficits or moderate deficits in postoperative tests. However, rats with bilateral damage to VPMpc and those with lesions just posterior to VPMpc had a profound deficit in their ability to detect NaCl and most of these animals failed to achieve criterion performance in 1,400 retraining trials. Prior studies have demonstrated that similar lesions alter preference for tastants. The present results indicate that such behavioral changes are due to a deficit in the ability of rats to detect the stimulus rather than a change in taste preference.