Objectives-To test the hypotheses that Parkinson's disease can differentially produce deficits in voluntary and rhythmic jaw movements, which involve different neuronal circuits, and that levodopa treatment improves specific components of the motor deficit.

Object While deep brain stimulation (DBS) has proven to be an effective treatment for many symptoms of Parkinson’s disease (PD), a deterioration of axial symptoms frequently occurs, particularly for speech and swallowing. These unfavorable effects of DBS may depend on the site of stimulation. We made quantitative measures of jaw velocity to compare the relative effectiveness of DBS in the globus pallidus internus (GPi) or the subthalamic nucleus (STN). Design Randomized, double-blind, and longitudinal, with matched healthy control subjects Methods The peak velocities of self-scaled and externally-scaled jaw movements were studied in 27 PD patients before and after 6 months of bilateral DBS in the GPi or the STN. A mixed-effects model was used to identify differences in jaw velocity before DBS surgery (baseline) while off and on levodopa therapy, and after 6 months of DBS (postoperative) during four treatment conditions (off- and on-levodopa states with and without DBS). Results Self-scaled jaw velocity was impaired by the DBS procedure in STN; velocity was significantly decreased across all postoperative conditions compared to either the off- and on-levodopa baseline conditions. In contrast, the GPi group postoperatively was generally faster than the baseline off levodopa state. Turning the DBS off and on had no effect on jaw velocity in either group. Unlike baseline, levodopa therapy postoperatively no longer increased jaw velocity in either group, and this lack of effect was not related to postoperative changes in dose. The externally-scaled jaw velocity was little affected by PD, but DBS still slightly affected performance, with the STN group significantly slower than the GPi group for most conditions. Conclusions Our results suggest that either the electrode implant in STN or the subsequent period of continuous STN stimulation negatively affected voluntary jaw velocity, including the loss of the preoperative levodopa induced improvement. While the GPi group showed some improvement in voluntary jaw velocity postoperatively, their performance during the combination of DBS and levodopa was not different than their best medical management presurgery. The results have implications for DBS target selection, particularly for those patients with oromotor dysfunctions.

DBS in either the globus pallidus internus or the subthalamic nucleus induces improvements in bradykinesia of specific components of postural and oromotor control, which also can be measured by the postural and orofacial UPDRS items. In some Parkinson's disease patients, DBS results in improvements in force or amplitude control, although these changes are not reflected in changes in UPDRS postural and orofacial items. A battery of quantitative and clinical tests must be used to evaluate the effects of DBS on axial motor control adequately.

This review summarizes some of the recent advances in the neurobiology of memory. Current research helps us to understand how memories are created and, conversely, how our memories can be influenced by stress, drugs, and aging. An understanding of how memories are encoded by the brain may also lead to new ideas about how to maximize the long-term retention of important information. There are multiple memory systems with different functions and, in this review, we focus on the conscious recollection of one's experience of events and facts and on memories tied to emotional responses. Memories are also classified according to time: from short-term memory, lasting only seconds or minutes, to long-term memory, lasting months or years. The advent of new functional neuroimaging methods provides an opportunity to gain insight into how the human brain supports memory formation. Each memory system has a distinct anatomical organization, where different parts of the brain are recruited during phases of memory storage. Within the brain, memory is a dynamic property of populations of neurons and their interconnections. Memories are laid down in our brains via chemical changes at the neuron level. An understanding of the neurobiology of memory may stimulate health educators to consider how various teaching methods conform to the process of memory formation.