Anatomical Correlates of Uncontrollable Laughter With Unilateral Subthalamic Deep Brain Stimulation in Parkinson's Disease

Movement-related increases in subthalamic activity optimize locomotion

The subthalamic nucleus (STN) is traditionally thought to restrict movement. Lesion or prolonged STN inhibition increases movement vigor and propensity, while optogenetic excitation has opposing effects. However, STN neurons often exhibit movement-related increases in firing. To address this paradox, STN activity was recorded and manipulated in head-fixed mice at rest and during self-initiated and self-paced treadmill locomotion. We found that (1) most STN neurons (type 1) exhibit locomotion-dependent increases in activity, with half firing preferentially during the propulsive phase of the contralateral locomotor cycle; (2) a minority of STN neurons exhibit dips in activity or are uncorrelated with movement; (3) brief optogenetic inhibition of the lateral STN (where type 1 neurons are concentrated) slows and prematurely terminates locomotion; and (4) in Q175 Huntington's disease mice, abnormally brief, low-velocity locomotion is associated with type 1 hypoactivity. Together, these data argue that movement-related increases in STN activity contribute to optimal locomotor performance.

Movement-related increases in subthalamic activity optimize locomotion

The subthalamic nucleus (STN) is traditionally thought to restrict movement. Lesion or prolonged STN inhibition increases movement vigor and propensity, while ontogenetic excitation typically has opposing effects. Subthalamic and motor activity are also inversely correlated in movement disorders. However, most STN neurons exhibit movement-related increases in firing. To address this paradox, STN activity was recorded and manipulated in head-fixed mice at rest and during self-initiated treadmill locomotion. The majority of STN neurons (type 1) exhibited locomotion-dependent increases in activity, with half encoding the locomotor cycle. A minority of neurons exhibited dips in activity or were uncorrelated with movement. Brief optogenetic inhibition of the dorsolateral STN (where type 1 neurons are concentrated) slowed and prematurely terminated locomotion. In Q175 Huntington's disease mice abnormally brief, low-velocity locomotion was specifically associated with type 1 hyperactivity. Together these data argue that movement-related increases in STN activity contribute to optimal locomotor performance.

A Neuroanatomy of Positive Affect Display – Subcortical Fiber Pathways Relevant for Initiation and Modulation of Smiling and Laughing

Background

We here report two cases of stimulation induced pathological laughter (PL) under thalamic deep brain stimulation (DBS) for essential tremor and interpret the effects based on a modified neuroanatomy of positive affect display (PAD).

Objective/Hypothesis

The hitherto existing neuroanatomy of PAD can be augmented with recently described parts of the motor medial forebrain bundle (motorMFB). We speculate that a co-stimulation of parts of this fiber structure might lead to a non-volitional modulation of PAD resulting in PL.

Methods

We describe the clinical and individual imaging workup and combine the interpretation with normative diffusion tensor imaging (DTI)-tractography descriptions of motor connections of the ventral tegmental area (VTA) (n = 200 subjects, HCP cohort), [[¹⁸F] fluorodeoxyglucose (¹⁸FDG)] positron emission tomography (PET), and volume of activated tissue simulations. We integrate these results with literature concerning PAD and the neuroanatomy of smiling and laughing.

Results

DBS electrodes bilaterally co-localized with the MB-pathway (“limiter pathway”). The FDG PET activation pattern allowed to explain pathological PAD. A conceptual revised neuroanatomy of PAD is described.

Conclusion

Eliciting pathological PAD through chronic thalamic DBS is a new finding and has previously not been reported. PAD is evolution driven, hard wired to the brain and realized over previously described branches of the motorMFB. A major relay region is the VTA/mammillary body complex. PAD physiologically undergoes conscious modulation mainly via the MB branch of the motorMFB (limiter). This limiter in our cases is bilaterally disturbed through DBS. The here described anatomy adds to a previously described framework of neuroanatomy of laughter and humor.

Non-motor Adverse Effects Avoided by Directional Stimulation in Parkinson's Disease: A Case Report

Introduction

Deep brain stimulation (DBS) is widely used for treatment of advanced, medication-refractory Parkinson's disease (PD). However, a significant proportion of patients may suffer adverse effects; up to 10% will present one or more transient or permanent neurobehavioral events.

Patient and Methods

In our case study, a 44-year-old woman diagnosed with PD 6 years previously who was suffering from motor fluctuations, dyskinesia, and freezing of gait episodes was submitted for DBS and implanted with directional electrodes. Intraoperative local field potentials (LFPs) were recorded. After surgery, conventional monopolar revision was performed. Preoperative 3T MRI studies and postoperative 3D and X-ray data were integrated using the Guide DTI software application (Brainlab), and diffusion tensor imaging tractography traced from cortical areas to each subthalamic nucleus (STN) using Elements software (Brainlab).

Results

We observed that left STN stimulation in the ring mode significantly improved motor symptoms, but the patient presented uncontrollable mirthful laughter. Stimulation was then switched to the directional mode; laughter remained when using the more posteromedial contact (3-C+) but not 2-C+ or 4-C+ at the same parameters. Interestingly, LFP recordings showed the highest beta-band activity over contacts 4 and 2, and very scarce beta power over contact 3. The orientation of the directional leads was selected based on the 3D postoperative X-rays. Associative fibers showed the shortest distance to contact number 3.

Conclusion

Stimulation of the STN can affect motor and associative loops. The use of directional electrodes is a good option to avoid not only undesirable capsular or lemniscal effects, but also limbic/associative events. Oscillatory activity in the beta range that preferentially takes place over the somatomotor STN region and is closely related to motor improvement, provides a reliable guide for optimizing the DBS programming. The importance of the exact location of electrical stimulation to determine the non-motor symptoms such as mood, apathy, attention, and memory, as well as the usefulness of biological markers such as LFP for optimal programming, is discussed in relation to this case.

Case Studies in Neuroscience: Lack of inhibitory synaptic plasticity in the substantia nigra pars reticulata of a patient with lithium-induced tremor

Tremor is a well-known side effect from many psychiatric medications, including lithium and dopamine antagonists. In patients whose psychiatric symptoms are stabilized and only respond to certain medications, deep brain stimulation may offer relief of the consequent motor complications. We report the case of an elderly male with disabling tremor related to lithium therapy for bipolar affective disorder, who was subsequently treated with deep brain stimulation. In this patient, we obtained recordings from the substantia nigra pars reticulata and performed a high-frequency stimulation protocol that robustly elicits long-term potentiation (LTP)-like changes in patients with Parkinson's disease. We hypothesized that in this patient, who did not have Parkinson's disease, the levels of inhibitory plasticity would be much greater. However, we found an unanticipated lack of plasticity in the patient with lithium-induced tremor, compared with two de novo control patients with Parkinson's disease. This patient was successfully treated with deep brain stimulation in the vicinity of the ventral oral posterior nucleus, an area of the thalamus that receives inputs from the basal ganglia. We postulate that the lithium-induced blockade of LTP may bring about motor complications such as tremor while simultaneously contributing to the therapeutic mechanism for treating the symptoms of psychiatric disorders such as bipolar affective disorder.NEW & NOTEWORTHY Use of a dual-microelectrode technique enabled us to compare long-term potentiation (LTP)-like changes in a patient with lithium-induced tremor to that of patients with Parkinson's disease. This study corroborated the findings in rodent brain slices that chronic lithium treatment may block LTP. Whereas a deficit in LTP may underlie the therapeutic mechanism for treating psychiatric disorders such as bipolar affective disorder, it may simultaneously contribute to consequent appearance of tremor.