Journal Article

Spontaneous low threshold spike bursting in awake humans is different in different lateral thalamic nuclei

Kim, J. H., Taghva, A., Ohara, S., Lenz, F. A.

2007

Overview

Spontaneous action potential bursts associated with low threshold calcium spikes (LTS) occur in multiple human lateral thalamic nuclei, each with different physiologic characteristics. We now test the hypothesis that different patterns of spontaneous LTS bursting occur in these nuclei during awake surgery in patients with essential tremor and the arm at rest. This protocol was chosen to minimize the effect of the patient's disease upon thalamic activity which is a potential confound in a surgical study of this type. Neuronal activity was studied in the human thalamic nuclei receiving somatic sensory input (Vc, ventral caudal), input from the deep cerebellar nuclei (Vim, ventral intermediate), or input from the pallidum (Vo, ventral oral). In each nucleus the burst rates were significantly greater than zero. Burst rates were higher in Vc than in Vim, while firing rates were lower. These findings suggest that neurons in Vc are hyperpolarized and have more frequent inhibitory events. Pre-burst inter-spike intervals (ISIs) were significantly longer in Vc, but were significantly shorter when corrected for the average ISIs between bursts (burst rate/inverse of the primary event rate). These results suggest that inhibitory events in Vc are of lower magnitude relative to a hyperpolarized resting membrane potential. Studies in many species demonstrate that input from the pallidum to the thalamus is inhibitory, suggesting that input to Vo is predominantly inhibitory. However, neurons in Vo have neither slower firing rates nor more frequent LTS bursts. Previous studies have found that spontaneous LTS is similar between classes of neurons within Vc, as defined by their response to thermal and painful stimuli. The differences in spontaneous LTS between human nuclei but not between functional classes within a nucleus may be a basic organizing principle of thalamic inhibitory circuitry.

• Publisher: Springer,Springer Nature B.V
• Subject: Action potential / Action Potentials - physiology / Adult / Aged / Aged, 80 and over / Analysis of Variance / Anatomy / Biological and medical sciences / Calcium / Calcium signalling / Central nervous system / Cerebellum / Deep Brain Stimulation - methods / Dismissal / Essential Tremor - physiopathology / Essential Tremor - therapy / Female / Firing pattern / Fundamental and applied biological sciences. Psychology / Humans / Inhibition / Lateral Thalamic Nuclei - physiopathology / Lateral Thalamic Nuclei - radiation effects / Male / Membrane potential / Middle Aged / Motor control and motor pathways. Reflexes. Control centers of vegetative functions. Vestibular system and equilibration / Neurons / Pallidum (ventral) / Patients / Resting / Retrospective Studies / Sensory Thresholds - physiology / Sensory Thresholds - radiation effects / Surgery / Thalamic nuclei / Thalamus / Thresholds / Tremor / Vertebrates: nervous system and sense organs / Wakefulness