Brain stem auditory evoked potential monitoring during profound hypothermia and circulatory arrest.

The effects of decreased temperature on brain stem auditory evoked potentials (BAEP) have been previously described in mild to moderate hypothermia. This report describes BAEP monitoring during profound hypothermia (11 degrees C) and circulatory arrest for repair of an aortic arch aneurysm. Recording of BAEP were interpretable during cooling to 14 degrees C, and demonstrated increasing interpeak (I-V) latency compatible with prolongation of brain stem conduction time. The changes rapidly returned to normal during rewarming from profound hypothermia, in a fashion similar to that seen after mild hypothermia, and therefore appear to be completely reversible.

Auditory brainstem evoked responses in autistic children.

Previous studies have implicated a brainstem dysfunction in the syndrome of autism. This study matched six autistic children with six normal children by age and sex to evaluate brainstem evoked response (BSER) to auditory stimuli. An evaluation of pure tone audiometric threshold showed no evidence of impairment; however, the electrophysiologic responses differed for the autistic and control groups. The BSER of the autistic children was remarkable for showing increased latency and markedly increased variability. The findings from this study add additional evidence of a brainstem dysfunction in autistic children, while the electrophysiologic variability supports the hypothesis of perceptual inconstancy.

Influence of thalamic cooling on sensory responses in association cortex.

Evoked responses to light flash, click, and paw stimuli were recorded in the four cortical association areas in the acutely prepared cat. Average evoked responses (AEP) for 100 trials were formed before, during, and after localized cooling in the midline thalamus. Cooling of the midline thalamus reduced the magnitude of responses to click and paw stimuli, and increased or did not change the responses to light flash. There was very little similarity in trial-to-trial fluctuations of EP magnitude across cortical areas, and cooling did not reduce the similarity that existed. Waveform similarity was reduced by cooling for responses across the cortex to a single stimulus modality, whereas similarity of responses in a single cortical area to all three stimuli was not changed. The temporal components of the AEP influenced by thalamic cooling were different for different stimuli and cortical locations. It was concluded that the midline thalamo-cortical projection through the centromedian area to association cortices is particularly well-differentiated for multisensory responses in a single cortical region, and that the system should not be thought of as nonspecific but as convergent or multisensory.