Protocol to assess the neurophysiology associated with multi-segmental postural coordination

Abstract

Anticipatory postural adjustments (APAs) stabilize potential disturbances to posture caused by movement. Impaired APAs are common with disease and injury. Brain functions associated with generating APAs remain uncertain due to a lack of paired tasks that require similar limb motion from similar postural orientations, but differ in eliciting an APA while also being compatible with brain imaging techniques (e.g., functional magnetic resonance imaging; fMRI). This study developed fMRI-compatible tasks differentiated by the presence or absence of APAs during leg movement. Eighteen healthy subjects performed two leg movement tasks, supported leg raise (SLR) and unsupported leg raise (ULR), to elicit isolated limb motion (no APA) versus multi-segmental coordination patterns (including APA), respectively. Ground reaction forces under the feet and electromyographic activation amplitudes were assessed to determine the coordination strategy elicited for each task. Results demonstrated that the ULR task elicited a multi-segmental coordination that was either minimized or absent in the SLR task, indicating that it would serve as an adequate control task for fMRI protocols. A pilot study with a single subject performing each task in an MRI scanner demonstrated minimal head movement in both tasks and brain activation patterns consistent with an isolated limb movement for the SLR task versus multi-segmental postural coordination for the ULR task.

Figure 1

Experimental tasks and variables. A) Supported leg raise task (SLR); B) Unsupported leg raise task (ULR), and; C) Schematic of the vertical ground reaction forces under the feet (Fz) as well as representative EMG. The graphs of representative EMG illustrate the task dependence and temporal characteristics of EMG burst activity for muscles of the leg: from top to bottom, the ipsilateral long-head of biceps femoris (BFM), the ipsilateral rectus femoris (RFM), the contralateral BFM, and the contralateral RFM. Black traces represent responses during the ULR task; gray traces represent responses during the SLR task. Time 0 represents movement onset. The dashed black vertical line indicates the start of the PRE-movement epoch (−200 ms), while the solid black vertical line represents the start of the movement-epoch (MOVE) (25 ms).

Figure 2

Summary of results. A) Mean integrated EMG amplitudes during the PRE epoch where the vertical axis represents the integrated EMG amplitudes of each muscle in millivolts and the horizontal axis lists each muscle with a prefix of “i” or “c”, representing the ipsilateral or contralateral side of the body, respectively. The black bars represent the grand averages for the ULR, and the gray bars represent the grand averages for the SLR; Muscles with significant task-by-epoch-by-muscle interactions are highlighted in bold text. B) Mean integrated EMG amplitudes during the MOVE epoch with the vertical and horizontal axes defines as in (A), and; C) Representative fMRI activation for “Go” minus “No-go” conditions during the SLR (i) and ULR (ii) tasks and for the “Go” condition of the ULR task minus the “Go” condition of the SLR task (iii). Red shaded areas indicate significance at the P < 0.05 level.