Inhibitory control is not lateralized in Parkinson's patients

Early‐Stage Parkinson's Patients Show Selective Impairment in Reactive But Not Proactive Inhibition

“…Second, there is another salient aspect that has been overlooked in the vast majority of previous work (see ref. for an exception). In a great number of cases, cardinal symptoms (rigidity, bradykinesia, resting tremor, and postural changes) of PD develop unilaterally either on the left or the right side of the body .…”

“…Because it has been hypothesized that inhibitory control of manual movements relies on a right‐lateralized frontal−basal ganglia–thalamic pathway, it follows that lateralized PD patients are an ideal population in which to test the role of the right hemisphere in action countermanding. Recently, Mirabella and colleagues compared inhibitory performance of right‐dominant and left‐dominant PD patients (RPD and LPD, respectively) in the middle stage of the disease (Hoehn and Yahr stages 2 or 3), and they did not find any difference in either reactive or proactive inhibition between LPD and RPD patients even though the patients were impaired with respect to healthy controls. The authors concluded that inhibition does not rely solely on the right hemisphere but on cooperation between the 2 hemispheres .…”

“…Recently, Mirabella and colleagues compared inhibitory performance of right‐dominant and left‐dominant PD patients (RPD and LPD, respectively) in the middle stage of the disease (Hoehn and Yahr stages 2 or 3), and they did not find any difference in either reactive or proactive inhibition between LPD and RPD patients even though the patients were impaired with respect to healthy controls. The authors concluded that inhibition does not rely solely on the right hemisphere but on cooperation between the 2 hemispheres . An objection to this result is that the absence of difference in inhibitory control between RPD and LPD patients could be ascribed to the fact that even though symptoms in these patients were pronounced asymmetric, both hemispheres were affected.…”

“…In most of them, the participants have to execute an action to respond to go‐signals (no‐stop trials), whereas in a minority of trials they have to suppress the preplanned action if a stop‐signal follows the go‐signal (stop trial). The reaching‐arm version of this task allows the simultaneous assessment of reactive and proactive inhibition . The former is quantified by the time it takes to cancel an action, the stop‐signal reaction time (SSRT), which is estimated using the race model .…”

“…It has been repeatedly shown that in healthy participants, go‐only trials RTs are shorter and MT are longer than in no‐stop trials . In contrast, in advanced PD patients or patients with unilateral deep brain stimulation, this optimization of costs and benefits (shorter RTs are compensated by longer MTs and vice versa) is impaired. This seems to be a very sensitive tool for assessing proactive control (but see ref.…”