Abstract
A primate study reported the existence of neurons from the dorso-lateral prefrontal cortex which fired prior to executing categorical action sequences. The authors suggested these activities may represent abstract level information. Here, we aimed to find the neurophysiological representation of planning categorical action sequences at the population level in healthy humans. Previous human studies have shown beta-band event-related desynchronization (ERD) during action planning in humans. Some of these studies showed different levels of ERD according to different types of action preparation. Especially, the literature suggests that variations in cognitive factors rather than physical factors (force, direction, etc) modulate the level of beta-ERD. We hypothesized that the level of beta-band power will differ according to planning of different categorical sequences. We measured magnetoencephalography (MEG) from 22 subjects performing 11 four-sequence actions - each consisting of one or two of three simple actions - in 3 categories; ‘Paired (ooxx)’, ‘Alternative (oxox)’ and ‘Repetitive (oooo)’ (‘o’ and ‘x’ each denoting one of three simple actions). Time-frequency representations were calculated for each category during the planning period, and the corresponding beta-power time-courses were compared. We found beta-ERD during the planning period for all subjects, mostly in the contralateral fronto-parietal areas shortly after visual cue onset. Power increase (transient rebound) followed ERD in 20 out of 22 subjects. Amplitudes differed among categories in 20 subjects for both ERD and transient rebound. In 18 out of 20 subjects ‘Repetitive’ category showed the largest ERD and rebound. The current result suggests that beta-ERD in the contralateral frontal/motor/parietal areas during planning is differentiated by the category of action sequences.
Highlights
We found for each subject the channel and frequency with the most prominent betaERD by calculating the maximum event-related desynchronization (ERD) value within the betaband (15, 30 Hz) during visual cue display (0.0, 0.8 s), from beta-band power time-course averaged by all trials
There was no difference in error rates across categories (F(2,63) = 0.04, p = 0.96). the errors were divided into two types; performance error and inhibition error
Subjects tended to make more inhibition errors for ‘Repetitive’ (84 % of all ‘Repetitive’ errors) than the other two (63 % and 53 % for all of ‘Paired’ and ‘Alternative’ errors, respectively), a paired-sample T-test did not confirm that the error rates for any of the error types were significantly different among categories (p . 0.05)
Summary
1. Activity Before Action The word ‘Animal’ in Korean and Japanese is expressed by a set of two Chinese characters ( ), which means ‘‘moving object’’. We plan before taking actions, making inferences about the consequences of our movements. Tanji and colleagues have been investigating the role of the prefrontal and non-primary motor areas in motor planning [2,3,4,5]. These papers showed that nonprimary cortices and prefrontal cortex in monkeys have important roles in pre-movement planning. Subsequent studies focused on the non-primary motor cortices, and implemented tasks which involved cognitive aspects to planning movements [3,6]
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