R.R. Tasker

Abnormal single-unit activity recorded in the somatosensory thalamus of a quadriplegic patient with central pain

We have performed single unit analysis of the activity of cells located in the ventral nuclear group of thalamus in a patient with dysesthetic pain below the level of a clinically complete traumatic spinal cord transection at C5. Cells located in the parasagittal plane 14 mm lateral to the midline responded to tactile stimulation in small facial and intraoral receptive fields, which were characteristic of patients without somatosensory abnormality [30]. In this patient the 16 mm lateral parasagittal plane contained cells with receptive fields located on the occiput and neck instead of the upper extremity as would normally be expected. Cells with receptive fields on the neck and occiput had not previously been observed in recordings from single units (n = 531) responding to somatosensory stimulation [30]. Thus, on the basis of their location in a region of thalamus which normally represents parts of the body below the level of the spinal cord transection and their unusual receptive fields adjacent to these same parts of the body, we propose that the cells in the 16 mm lateral plane have lost their normal afferent input. Analysis of the autopower spectra of spike trains indicates that cells in the 16 mm lateral plane exhibited a higher mean firing rate and greater tendency to fire in bursts than cells in the 14 mm lateral plane (P less than 0.005). Finally, electrical stimulation at the recording sites in the 16 mm lateral plane evoked a burning sensation in the occiput, neck and upper extremity. These results suggest that regions of thalamus which have lost their normal somatosensory input contain neurons which exhibit abnormal spontaneous and evoked activity and that electrical stimulation of these regions can produce the sensation of burning dysesthesia.

What Happened to VIM Thalamotomy for Parkinson's Disease?

A prospective review of 75 of 190 parkinsonian patients undergoing unilateral thalamotomy was displayed with a computer graphics technique examining three equal consecutive groups from the pre-, early, and late L-dopa eras. Histograms for average function and scattergrams of individual patients performance preoperatively and up to 2 years postoperatively were prepared. No ipsilateral effects or consistent iatrogenic deterioration of any function were identified. 2 years after surgery, 82% had no tremor in the contralateral fingers or hand and 7% had almost no tremor; contralateral tremor elsewhere was infrequent. Rigidity and manual dexterity improved less strikingly, the latter only reflecting abolition of tremor; locomotion, speech, facial movement and handwriting did not improve. There was no mortality, but 8% had persistent significant complications. VIM thalamotomy remains the treatment of choice for severe drug-resistant parkinsonian tremor.

Third Ventricular Width and the Thalamocapsular Border

65 patients were selected to assess variations in third ventricular width. The patients suffered from various extrapyramidal movement disorders, and all had undergone stereotactic VL thalamotomies. Third ventricular width was correlated with age, sex, diagnosis and intercommissural distance. Based upon the analysis of somatosensory response mappings, a medial displacement of the thalamocapsular border was demonstrated for patients with narrow third ventricles.

The Physiological Basis of VIM Thalamotomy for Involuntary Movement Disorders

Physiological corroboration of the lesion site for thalamotomy [12, 20] offers an opportunity to study sensorimotor integration at the thalamic level. The target [8–10, 17, 21, 25, 27, 40, 41, 46, 53, 55, 57] where a 4–6 mm diameter lesion abolishes various types of tremor in a high proportion of cases [27, 38, 57] and ameliorates other dyskinesias, lies just rostral to ventrocaudal nuclear (VC) representation of lips or manual digits at or a little above the intercommissural (ACPC) line in nucleus ventralis intermedialis (VIM) or adjacent oralis posterior (VOP) of thalamus: It remains controversial whether lesions here arrest the progress of Parkinson’s disease [38, 51]. The results of macro- and microstimulation and of microelectrode recording in the target area will be interpreted in the light of sensorimotor integration.

The role of feedback in the tremor frequency activity of tremor cells in the ventral nuclear group of human thalamus.

Close loop system identification techniques have been used to identify the presence of feedback in the firing pattern of thalamic tremor cells recorded in parkinsonian tremor patients.

Computerized Graphic Display of Physiological Data Collected during Human Stereotactic Surgery

An on-line computerized graphic display has been developed for use during stereotactic operations. This depicts in the form of figurine charts and alph-numeric symbols, appropriately oriented on saggital brain diagrams, the results of serial threshold stimulation of the brain. The display facilitates choice of target sites and the data can be stored in a tape library from which search-and-plot programs can be activated for any type or combination of types of response.

Percutaneous Cervical Cordotomy

Cordotomy should be reserved for patients with intractable pain resistant to conservative treatment that is not of a dysaesthetic type. The high cervical percutaneous technique permits exploitation of the principles of stereotactic surgery, especially physiological localization of the lesion site. The induction by 100 Hz stimulation of a warm or cool tingling in some portion of the contralateral half of the body without muscle tetanization ensures location within the spinothalamic tract while attention to the somatotopographic organization of the responses permits a certain degree of tailoring of the extent of analgesia to the patients needs. During 264 consecutive procedures the spinothalamic tract was successfully located in 99% with a 0.3% incidence of significant persistent paresis.

Simultaneous Recordings in the Human Thalamus and Cortex of an Early Evoked Component

Evoked potentials have been simultaneously recorded in 9 patients at thalamic and scalp cortical levels. The similarity of wave characteristics at both levels seems to demonstrate the origin in a thal

Techniques for the Analysis of Spike Trains in the Human Central Nervous System

This paper describes two methods, the cross correlogram and spectral cross correlation techniques, for correlating spike trains and analog signals recorded at Operation.

Sensory Organization of the Human Thalamus

A computerized program has been developed for on-line display and tape-library storage of stimulation-mapping data collected during stereotactic procedures. Using computer-generated displays of pooled clinical physiological data it has been possible to map through the upper midbrain and thalamus the lemniscal, spinoquintothalamic, auditory, vestibular, visual, extrapyramidal, and motor pathways, as well as the location of the pia. Each system is recognizable by a stereotyped, artificial, somatotopically organized stimulation-induced response that is devoid of modality information and independent of the site and parameters of stimulation.