Nombela et al., from Hospital Clínico San Carlos, Toronto Western Hospital, reported a Parkinson's disease (PD) patient diagnosed with mild cognitive impairment who underwent DBS surgery targeting the Globus pallidus internus (GPi; to treat motor symptoms) and the nucleus basalis of Meynert (NBM; to treat cognitive symptoms) using a single electrode per hemisphere.
Compared to baseline, 2-month follow-up after GPi stimulation was associated with motor improvements, whereas partial improvements in cognitive functions were observed 3 months after the addition of NBM stimulation to GPi stimulation.
In a 71-year-old man with slowly progressive Parkinson-dementia syndrome, 2 electrodes were inserted into the nucleus basalis of Meynert in addition to electrodes in the subthalamic nucleus.
Turning on the subthalamic nucleus electrodes improved motor symptoms but left cognitive performance almost unchanged. Turning on electrical stimulation of the nucleus basalis of Meynert resulted in markedly improved cognitive functions. The improvement in attention, concentration, alertness, drive, and spontaneity resulted in the patient's renewed enjoyment of former interests and enhanced social communication.
Such a broad effect on cognition is consistent with ample experimental evidence revealing that the nucleus basalis of Meynert provides cholinergic innervation to the cortical mantle, complemented by glutaminergic and gamma-aminobutyric acid-transmitting projections from the basal forebrain. These projections provide background tuning facilitating cortical operations. Furthermore, nucleus basalis of Meynert stimulation paired with sensory stimuli can accomplish persistent reorganization of specific processing modules. The improvements in cognitive and behavioral performance in our patient are likely to be related to the effects of stimulating residual cholinergic projections and cell bodies in the nucleus basalis of Meynert 2).
In a case report published in 1985—prior to the current modern era of DBS—Turnbull et al. 3) were the first to target this region, implanting a stimulating electrode in the left NBM in a single patient with AD. Stimulation was applied in a cyclic fashion for 9 months. Compared with the nonstimulated right side, glucose utilization was relatively preserved in the left cerebral hemisphere, particularly in the temporal and parietal areas. However, the authors did not find any convincing evidence of clinical improvement on memory or other cognitive measures at the end of the follow-up period.