Comparison of DOMS-related activation by contraction and physical stimulation in M1 and S1.

<p>Multi studies of activations by both stimuli in a standardized Talairach brain shown as activation maps <b>(a–f)</b> and as increases in hemodynamic response function <b>(g–j)</b>. Clusters were calculated by GLM contrasts between painful and non-painful stimulation conditions (t≥5). <u>Legend</u>: Light blue: activation by painless contraction; dark blue: activation by painless physical stimulation; magenta: common activation by both painless stimuli; dark green: activation by painful contraction; light green: activation by painful physical stimulation; orange: common activation by both painful stimuli. <b>(a)</b> coronal section showing orientation of sagittal sections b and c and transverse sections d, e and f. <b>(b, c)</b> Sagittal sections of the parasagittal cortical areas of both hemispheres illustrating the area somatotopically related to the respective thigh (M1 and S1). Painful stimulation –contraction as well as physical stimulation- activate areas expanding into the cingulate cortex. <b>(d, e, f)</b> Painless physical stimulation is centred in postcentral gyrus S1. Both contraction and physical stimulation activate precentral M1. Activation in response to painful stimulation expands over large areas of M1 and S1 with physical stimulation resulting in more widespread activation than voluntary contraction. (g–j) timeline of the BOLD-signal (average over 5 stimulus periods) in the respective clusters marked with circles in map (d). Red, painful condition, blue, non-painful condition, black bar, stimulus condition in event-related block design; error bars represent S.E.M. (g) contraction of the left thigh (control) and contraction of the right painful thigh both lead to an increase in BOLD signal in the right hemisphere in areas of the pre- and postcentral gyrus (blue timeline: control; red timeline: painful contraction of right-sided quadriceps); (h) painful contraction of the right thigh (red timeline) reveals a large increase in BOLD signal in somatotopically related areas of the left pre- and postcentral gyrus (red), similarly, the control contraction leads to coactivation in the left hemisphere (blue timeline); (i) BOLD signal in response to left-sided and right-sided physical stimulation (blue timeline and red timeline); (j) right-sided painful physical stimulation (red timeline), but not left-sided physical stimulation (blue timeline), leads to an increase in BOLD signal in the left-sided somatotopically related areas. Note: panels d-f were magnified by 40% in comparison to a–c.