Sensory and cognitive components of the CO2 laser evoked cerebral potential

We recorded CO2 laser evoked cerebral potentials in 6 healthy subjects using both a standard technique and an oddball paradigm. In the standard technique stimuli were aimed at the dorsum of the left hand with the subject passive; in the oddball paradigm, target infrequent stimuli (P = 0.15) were directed to one side of the dorsum of the left hand and the subject was instructed to count their occurrence, the frequent stimulus being delivered to the other side of the hand. In both standard and oddball frequent recordings, CO2 laser evoked potentials were a well-formed negative-positive complex with a peak latency and amplitude around 305 msec (to positivity) and 32 microV respectively. However, in the oddball target task a later potential was also recorded, with a mean latency and amplitude of 621 msec and 24 microV respectively which we believe to be a laser oddball potential. These results demonstrate that the CO2 potential is not altered by manipulations of attention to any significant extent and suggests that it is therefore closely related to the primary sensory input. They also provide further evidence of the non-specificity of the oddball potential across sensory modalities.