Figure 7.

Phase precision of the stimulus pulse affects the strength of beta amplitude modulation. Increased stimulus phase precision leads to stronger modulation of beta amplitude. A, Example patient showing both enhanced suppression and amplification of beta amplitude when using narrower phase bins. Bins were widened or narrowed around the mean suppressing and amplifying phase (black dots). Stimulus phase was defined as follows: (left) half the oscillation cycle, (middle) ¼ the oscillation cycle, (right) ⅛ the oscillation cycle. Blue hues represent the suppressing phase; orange hues represent the amplifying phase. Amplitude modulation was only dependent on number of consecutive pulses when using ⅛ the oscillation cycle (amplifying phase: 2 bins, χ² = 1.24, p = 0.941; 4 bins, χ² = 2.05, p = 0.842; 8 bins, χ² = 9.89, p = 0.0423; suppressing phase, 2 bins, χ² = 5.23, p = 0.388; 4 bins, χ² = 10.99, p = 0.0517; 8 bins, χ² = 12.62, p = 0.0272, Kruskal–Wallis test). B, Median suppressing and amplifying effects using phase bins half a cycle wide across eight patients. Neither beta suppression (χ² = 6.33, p = 0.276) nor amplification (χ² = 6.62, p = 0.250) was dependent on the number of consecutive stimuli (Kruskal–Wallis test). This is in contrast to results seen in Figure 5 where narrower phase bins (¼ cycle wide) were used. C, Median suppressing and amplifying effects using phase bins ⅛ cycle wide across eight patients. Because it was unlikely to see three or more consecutive stimulus cycles using the narrower phase bins, <5 patients were included in many of these bins. For the suppressing phase: first pulse, n = 8 patients; second pulse, n = 8 patients; third pulse, n = 4 patients; fourth pulse, n = 2 patients; fifth pulse, n = 1 patient; sixth pulse, n = 1 patient. For the amplifying phase: first pulse, n = 8 patients; second pulse, n = 6 patients; third pulse, n = 3 patients; fourth pulse, n = 2 patients; fifth pulse, n = 1 patient; sixth pulse, n = 1 patient.