Abolition of a conditioned, surface-negative, cortical potential during cryogenic blockade of the non-specific thalamo-cortical system

Cryoprobes were implanted bilaterally in the region of the inferior thalamic peduncle (ITP) of three chronic cat preparations in order to block the non-specific thalamo-cortical system. Three other chronic animal preparations had cryoprobes placed more laterally in this forebrain region in the medial part of the anterior limb of the internal capsule. All six animals had stimulating electrodes placed in nucleus ventralis lateralis (VL) to produce augmenting responses and in nucleus centralis medialis (NCM) to produce recruiting responses. Transcortical recording electrodes were implanted ipsilaterally in the anterior sigmoid, coronal, anterior lateral and anterior suprasylvian cortices. 1. 1. Stimulation of NCM produced either no sustained steady-potential shift or a small positive one, whereas repetitive stimulation of VL produced a train of augmenting responses superimposed upon a large, negative, steady-potential shift which was followed after the cessation of stimulation by a post-stimulus wave of 300–400 msec duration. 2. 2. Reversible cryogenic blockade in the region of the ITP sufficient to abolish recruiting responses abolished or markedly reduced the VL-elicited steady potential and post-stimulus wave recorded in the anterior sigmoid and coronal cortices but did not affect the simultaneously recorded positive-negative augmenting-response components. Cryogenic blockade in the medial part of the anterior limb of the internal capsule did not affect the VL-elicited steady potential or post-stimulus wave, although it did reduced the amplitude of the augmenting response in the anterior sigmoid cortex. 3. 3. The three animals with cryoprobes in the ITP were exposed to a sensory-sensory conditioning paradigm in which a tone was reinforced with a mild electric shock to the skin of the neck. During early conditioning, surface-negative steady-potentials were recorded in the anterior sigmoid, coronal, and anterior lateral, i.e., marginal, cortices. After 500 additional trials, the surface-negative response had a longer latency of onset, occurring just before the start of the shock, and after overtraining, the conditioned negative response was recorded only in the frontal cortical region (anterior sigmoid). 4. 4. Cryogenic blockade in the region of the ITP abolished or markedly reduced the amplitude of the conditioned negative response recorded in the frontal cortical area during both early conditioning and overtraining. 5. 5. During ITP blockade, the simultaneous effect on the steady-potential shift, post-stimulus wave, and conditioned cortical response suggests a common underlying mechanism. 6. 6. It was shown that the VL-elicited steady-potential shift and post-stimulus wave recorded in the frontal and sensory-motor cortex, as well as the conditioned negative response recorded in the frontal cortical region, are affected by the non-specific thalamo-cortical system, a system that from previous studies has been shown to mediate recruiting responses, regulate specific sensory evoked potentials and underlie the performance of certain complex behavioral tasks. The previous work as well as the present is suggestive of a neural mechanism related to the focusing of attention, expectancy and selective perception.