Use of DC recording in the demonstration of functional specialization

This paper describes a rationale and methodology for the use of DC recording techniques to reveal patterns of cerebral functional specialization. Results from a number of recent experiments are described. In each of these studies 15 channels of DC potential were recorded from a widely spaced array of scalp-mounted Ag/AgCl electrodes. The duration of single trial recording was always 40 s although the paradigms involved continuous performance of a complex cognitive task. In this series of experiments we used the following tasks: both visually and aurally presented word target detection with classification on a semantic basis, recognition of 'famous' faces and discrimination of animal versus non-animal sounds. In each of these tasks the rate of presentation has been systematically varied to evaluate quantitative aspects of task demand. In general, the results from these studies demonstrate that DC recording does provide a method for assessing the degree of activation of different cortical regions at the same time. However, it appears that additional transformation of the data may be required to separate out a number of overlapping slow potentials to increase the sensitivity to more subtle aspects of the cognitive demand. Two different methods to perform the separation are described and applied.