Poster A103, Saturday, March 25, 5:00 – 7:00 pm, Pacific Concourse
Motor evoked potentials reflect changes in rapid inhibitory control during serial ordering
Lawrence P Behmer Jr.1, Matthew J C Crump1, K J Jantzen2, Sarah Martinez2, Rachel Walls2, Elisabeth Amir-Brownstein2, Andrew Jaye2, Mckaila Leytze2, Kathleen Lucier2; 1Brooklyn College of CUNY, 2Western Washington University
Theories of serial ordering assume all responses in a sequence are activated in parallel and held in a buffer for execution. An inhibition or timing process impedes responses in a graded fashion with earlier more active responses executed before more inhibited later responses. There is no direct evidence in humans that planned responses are inhibited as a function of serial order. The necessary evidence could be provided by a response activation “thermometer” measuring whether the current “temperature” or activation level is graded by position across all responses in the buffer. We used transcranial magnetic stimulation to probe the level of excitation for flexion of the right index finger (first dorsal interosius muscle mucle) during typing. Motor evoked potentials (MEPs) were recorded at the onset of typing 5-letter words and nonwords. A single letter typed by the right index finger varied across letter positions one to five. The amplitude of the MEP when the right index finger was used in letter positions one and two reflected the relatively active state of the FDI. MEP amplitude decreased monotonically with further increases in position. Interestingly we also found smaller MEPs when the right index finger was the first rather than second response, indicative of a rapid deactivation at the completion of a key press. This is the most direct human evidence to date corroborating inhibition/timing theories, showing that completed responses are rapidly deactivated and future responses are activated in a graded fashion as a function of serial position.
Topic Area: PERCEPTION & ACTION: Motor control