The beat goes on: Rhythmic modulation of cortical potentials by imagined tapping.

Abstract

A frequency analysis was used to tag cortical activity from imagined rhythmic movements. Participants synchronized overt and imagined taps with brief visual stimuli presented at a constant rate, alternating between left and right index fingers. Brain potentials were recorded from across the scalp and topographic maps made of their power at the alternation frequency between left and right taps. Two prominent power foci occurred in each hemisphere for both overt and imagined taps, one over sensorimotor cortex and the other over posterior parietal cortex, with homologous foci in opposite hemispheres arising from oscillations 180° out of phase. These findings demonstrate temporal isomorphism at a neural level between overt and imagined movements and illustrate a new approach to studying covert actions. Keywordscovert motor processes; motor imagery; synchronization tapping; movement-related brain potentials; frequency taggingThe present study is concerned with a type of motor-mind reading. We propose a new method for studying covert motor processes. The method employs movement-related brain potentials to monitor cortical motor areas in the absence of overt movement. Participation of these areas in specific covert acts is revealed by the temporal and spatial pattern of potentials. To illustrate the method, it is applied here to a type of covert motor process known as motor imagery or mental simulation. As will be seen, people can drive their cortical motor areas with a pattern quite similar to that during overt movement while producing little or no muscle activity. Moreover, the temporal relations observed between responses from different neural populations suggest that similar motor programs were run during overt and imagined actions.Correspondence concerning this article should be addressed to Allen Osman, Department of Psychology, University of Pennsylvania, 3401 Walnut Street, Suite 302C, Philadelphia, PA 19104. Email: aosman@psych.upenn NIH-PA Author ManuscriptNIH-PA Author Manuscript NIH-PA Author ManuscriptTo better explain why one would want to engage in motor-mind reading, we will provide some background on covert motor processes in general and motor imagery in particular. Details of the method then will be presented. Covert Motor ProcessesCovert motor processes are motor processes that occur with little or no overt movement or muscle activity. These cognitive processes are motoric in the sense that they are implemented by the same neural machinery involved in overt movement, and perform computations similar to those necessary to produce or control overt movement. Such processes are quite pervasive. For example, motor processes occur without immediate overt consequences when a movement is prepared and then held in readiness until the proper moment (e.g., Leuthold, Sommer, & Ulrich, 1996;Osman, Moore, & Ulrich, 1995 or inhibited before becoming overt (e.g., De Jong, Coles, Logan, & Gratton, 1990;Miller & Hackley, 1992;Osman, Bashore, Coles, Donchin, & Meyer, 1992). Sometimes motor processes are cover...

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