We investigated changes of impulsivity after deep brain stimulation (DBS) of the subthalamic nucleus (STN) in Parkinson's disease (PD) patients, distinguishing functional from dysfunctional impulsivity and their contributing factors.

DBS-STN is routinely used to treat motor complications in PD [1Benabid A.L., Chabardes S., Mitrofanis J., Pollak P. Deep brain stimulation of the subthalamic nucleus for the treatment of Parkinson's disease Lancet Neurol 2009 ;  8 (1) : 67-81 [inter-ref]

Cliccare qui per andare alla sezione Riferimenti]. However, its impact on impulsivity in PD patients is controversial [2Jahanshahi M., Obeso I., Baunez C., Alegre M., Krack P. Parkinson's disease, the subthalamic nucleus, inhibition, and impulsivity Mov Disord 2015 ;  30 : 128-14010.1002/mds.26049 [cross-ref]

Cliccare qui per andare alla sezione Riferimenti, 3Rossi P.J., Shute J.B., Opri E., Molina R., Peden C., Castellanos O., e al. Impulsivity in Parkinson's disease is associated with altered subthalamic but not globus pallidus internus activity J Neurol Neurosurg Psychiatry 2017 ;  88 : 968-97010.1136/jnnp-2016-315325 [cross-ref]

Cliccare qui per andare alla sezione Riferimenti, 4Broen M., Duits A., Visser-Vandewalle V., Temel Y., Winogrodzka A. Impulse control and related disorders in Parkinson's disease patients treated with bilateral subthalamic nucleus stimulation: a review Parkinsonism Relat Disord 2011 ;  17 : 413-41710.1016/j.parkreldis.2011.02.013 [cross-ref]

Cliccare qui per andare alla sezione Riferimenti].

Data of 33 PD patients treated by DBS-STN were studied before and 6 months after surgery: motor impairment, medication (dose and dopaminergic agonists), cognition, mood and occurrence of impulse control disorders. Impulsivity was assessed by the Dickman scale, which distinguishes functional impulsivity (FI), reflecting the potential for reasoning, premeditation and rapid action when the situation requires it, and dysfunctional impulsivity (DFI), reflecting the lack of prior reasoning, even when the situation demands it. The location of DBS leads was studied on postoperative MRI using a deformable histological atlas and by compartmentalization of the STN.

After DBS-STN, dysfunctional impulsivity was significantly increased (mean pre- and postoperative DFI scores 1.9±1.6 and 3.5±2.4, P<0.001) without change in functional impulsivity (mean pre- and postoperative FI scores 6.2±2.7 and 5.8±2.6). Factors associated with an≥2 increase in DFI score were: a low preoperative Frontal Assessment Battery score (P=0.03), a high preoperative on medication UPDRS score (P=0.02), and location of the left active contact in the ventral part of the STN (P=0.012).

Our study suggests that DBS-STN may have a different impact on both dimensions of impulsivity, worsening pathological impulsivity without altering physiological impulsivity. The increase in dysfunctional impulsivity may be favoured by the location of the electrode in the ventral, limbic, part of the STN.