Effects of subthalamic nucleus deep brain stimulation on cognitive function in patients with Parkinson's disease

Objective: To follow up the patients with Parkinson's disease (PD) who underwent subthalamic nucleus (STN) deep brain stimulation (DBS) therapy, and to compare the changes of cognitive function before and after this functional surgery.

Methods: The authors set up a series of clinical tests including unified Parkinson's disease rating scale (UPDRS) II & III, Hoehn & Yahr stage (H-Y stage), mini mental state examination (MMSE), Wechsler memory scale (WMS), serial reaction time task (SRTT), degraded picture naming (DPN), verbal fluency (VF), clock drawing test (CDT) to measure the performance of both clinical characteristics and cognitions 1 week before and 12 months after STN-DBS operation in 20 PD patients, matched with 20 healthy adults who just assessed by the neuropsychological tests.

Results: Activity of daily life (UPDRS II), motor manifestations (UPDRS HI) and disease condition (H-Y stage) were all significantly improved whether they were "on period" or "off period" (P<0.01). In the test of WMS, the memory quotient (MQ) scores of PD patients (88.10±16.70) were significantly lower (t=-3.187, P<0.01) than the control group (100.90±6.45). By SRTT test, the mean average response time (T_avg) of the control group, pre-operation and post-operation groups was (1.09±0.32) s, (1.58±0.83) s and (1.62±0.83) s, respectively. As to the comparison of the blocks, no changes were found within each group of PD (pro-F=0.329, P=0.964; post-F=0.377, P=0.945), by contrast, it had been proved to be statistically significant in the control group (F=2.316, P<0.05). The mean error rates of the control group, pre-operation and post-operation groups were 4.84%±4.27%, 9.76%±1.52% and 13.41%±1.11% respectively, and the control group was not different from pre-operation group (t=1.388, P=0.173) while significantly different compared with post-operation group (t=3.225, P<0.01). As for MMSE and DPN results, no significant benefits were obtained in the control, pre-operation and post-operation groups. In regard to VF, there was a statistically significant difference between control group and pre-operation group (Z=-2.927, P<0.01), and it was significantly worse after surgery (Z=-2.469, P=0.014). As for CDT, significant benefits were obtained in both pre-operation (Z=-2.762, P<0.01) and post-operation groups (Z=-2.165, P=0.03) compared with control group.

Conclusions: To some extent, STN-DBS can affect the cognition of PD patients, such as lowing VF, improving visual-spatial function and attention, a decreasing trend of implicit memory and executive function. Explicit memory is partly dissociated with implicit memory.