Oscillatory cortical changes during periodic limb movements

Periodic limb movements are a distinctive and frequent finding on polysomnography. The pathophysiology and clinical significance of these common sleep-related movements are not yet well understood. The brainstem, spinal cord, and peripheral nervous system may be implicated in the pathogenesis of periodic limb movements. The goal of our study was to probe if there is any participation of cortical mechanisms in the periodic limb movements. We focused the study on the analysis of electroencephalogram oscillations around the periodic limb movement.

We selected polysomnographic recordings of 6 patients diagnosed with periodic limb movements of sleep.

We analyzed the cortical activity offline after averaging 10-second segments, having the middle point with the beginning of each limb movement in non-rapid eye movement sleep, selecting exclusively samples without obvious arousals. In each patient, polysomnographic segments containing limb movements were selected from both slow-wave (stage 3-4) and lighter (stage 1-2) non-rapid eye movement sleep.

An increase in all the frequencies immediately after the limb movements, having the maximum 2.5 to 3 seconds after the beginning of the movement, was found. The slope started 1.5 to 2 seconds before the limb movements. The topography of this activity was different from the activity accompanying voluntary movements in the awake state. The meaning of this activity is uncertain, but one possibility is its relationship with microarousals or an increase of the sensory inputs. The beginning of the increase before the limb movements suggests that the cortex may be engaged during the neural changes associated with this kind of movement, though not playing a causal role.