Cortical Resource Allocation During Mental Rotation Determined by Magneto- and Electro- Encephalography

Of the many electrophysiological techniques employed for the assessment of cortical resource allocation, the probe paradigm has been especially useful. This technique involves the ensemble averaging of evoked responses to task-irrelevant probe stimuli presented to subjects actively performing a cognitive task. Based on the limited resources hypothesis of neuronal functioning, this methodology assumes that: (a) as task demands increase, the proportion of available cortical resources allocated to that task also increases, resulting in a concomitant decrease in the system’s capacity to respond to a simultaneously presented probe stimulus, and (b) reductions in the amplitude of the probe evoked response index the reallocation of resources for performance of the primary task. The utility of this method for evaluating hemispheric lateralization of functions in a variety of cognitive tasks has been previously demonstrated (for review see Papanicolaou and Johnstone, 1984). However, conclusions concerning relative hemispheric dominance that are based solely on the results of evoked potentials (EPs) have the added assumption that the measured electrical activity was indeed generated within the hemisphere over which it was recorded, an interpretation which can be problematic due to the conductive properties of the electrical potentials (Nunez, 1981).