Responses of neurons in the globus pallidus (GP) to cortical stimulation were recorded for the first time in humans. We performed microelectrode recordings of GP neurons in 10 Parkinson's disease (PD) patients and 1 cervical dystonia (CD) patient during surgeries to implant bilateral deep brain stimulation electrodes in the GP. To identify the motor territories in the external (GPe) and internal (GPi) segments of the GP, unitary responses evoked by stimulation of the primary motor cortex were observed by constructing peristimulus time histograms. Neurons in the motor territories of the GPe and GPi responded to cortical stimulation. Response patterns observed in the PD patients were combinations of an early excitation, an inhibition, and a late excitation. In addition, in the CD patient, a long-lasting inhibition was prominent, suggesting increased activity along the cortico-striato-GPe/GPi pathways. The firing rates of GPe and GPi neurons in the CD patient were lower than those in the PD patients. Many GPe and GPi neurons of the PD and CD patients showed burst or oscillatory burst activity. Effective cathodal contacts tended to be located close to the responding neurons. Such unitary responses induced by cortical stimulation may be of use to target motor territories of the GP for stereotactic functional neurosurgery. Future findings utilizing this method may give us new insights into understanding the pathophysiology of movement disorders.

Dystonia is a neurological disorder characterized by sustained or repetitive involuntary muscle contractions and abnormal postures. In the present article, we will introduce our recent electrophysiological studies in hyperkinetic transgenic mice generated as a model of DYT1 dystonia and in a human cervical dystonia patient, and discuss the pathophysiology of dystonia on the basis of these electrophysiological findings. Recording of neuronal activity in the awake state of DYT1 dystonia model mice revealed reduced spontaneous activity with bursts and pauses in both internal (GPi) and external (GPe) segments of the globus pallidus. Electrical stimulation of the primary motor cortex evoked responses composed of excitation and subsequent long-lasting inhibition, the latter of which was never observed in normal mice. In addition, somatotopic arrangements were disorganized in the GPi and GPe of dystonia model mice. In a human cervical dystonia patient, electrical stimulation of the primary motor cortex evoked similar long-lasting inhibition in the GPi and GPe. Thus, reduced GPi output may cause increased thalamic and cortical activity, resulting in the involuntary movements observed in dystonia.

A 38-year-old woman presented with a rare case of myositis ossificans in the temporal muscle manifesting as left temporal scalp mass with mild pain. The mass was elastic-hard and seemed to be located in the temporal muscle. Magnetic resonance imaging revealed a heterogeneously enhanced mass in the muscle. The tumor was resected. The histological diagnosis was myositis ossificans. The clinicopathological features of scalp myositis ossificans may mimic other soft tissue tumors, requiring care for the differential diagnosis.

A 20-year-old man presented with diplopia. Neurological examination revealed mild skew deviation and upbeat nystagmus. Computed tomography showed a clover-shaped isodense mass in the pineal region with homogeneous enhancement. The lesion was isointense on both T 1 -and T 2 -weighted magnetic resonance (MR) imaging with homogeneous enhancement by gadolinium-diethylenetriaminepentaacetic acid. Cerebral angiography showed no tumor staining. Serum and cerebrospinal fluid were negative for b-human chorionic gonadotropin, a-fetoprotein, and placental alkaline phosphatase. Open biopsy was performed using a right occipital transtentorial approach. Histological examination revealed a tumor consisting of clusters of germinoma cells, but with prominent infiltration of lymphocytes, plasma cells, and macrophages, and proliferation of small vessels. The histological diagnosis was germinoma with granulomatous reaction. MR imaging showed complete disappearance of the tumor after chemoradiotherapy. Neurosurgeons should be aware of this rare tumor to avoid misdiagnosis as granulomatous inflammation.