Abstracts

Rationale: Rationale: The function of the claustrum is not fully understood. There are reports of behavioral arrest in animals (Gabor AJ. et al. Electroenceph. Clin. Neurophysiol.;1964;17:513-519) and alteration of consciousness in human (Koubeissi MZ. et al. Epilepsy Behav. Elsevier; 2014;37:32–5) elicited by claustrum stimulation. In addition, there is a suggested role of the claustrum in epilepsy (Mohapel, P. et al. Epilepsia;2000; 41,1095–1101). The aim of our study was to assess the role of the claustrum on sustained attention and its involvement in alteration of consciousness that accompanies seizures. Methods: Methods: Adult male Sprague-Dawley rats (n=9) weighing 250-390 g were food-restricted to 85% of their baseline body weight before and throughout the behavioral training. The task consisted of nose poking inside an activated operandum for a sucrose pellet reinforcement to be delivered through the feeder. A within-subject design was used. When the rats reached criterion level of performance, tripolar electrodes were implanted in bilateral claustra and unipolar recording electrodes in bilateral hippocampal CA3 regions. The task was repeated with electrical stimulation of both claustra (50 Hz, 1-ms pulse width) at specific current intensities per session starting at 50 µA and increasing by 50 µA up to 200 µA then increasing by 200 increments to a maximum of 1000 µA. Similar testing protocol was repeated stimulating each claustrum separately. Generalized estimating equations (GEE) were used to assess the effect of stimulation of the claustrum on task scores. Results: Results: After confirming the accurate placement of electrodes, the data of four rats were analyzed. The performance score for the task could be between 0 to 100. The mean baseline score for all animals was 67 over 3 consecutive days before initiating the stimulation protocol. Bilateral and unilateral stimulation resulted in a decrease in task performance scores relative to rest sessions with an effect of -15.8 (p < 0.0001) and -15.2 (p < 0.0001), respectively. The magnitude of the decline being proportional to the current intensity (Figure). Additionally, there was no significant differences in baseline performance scores before and after HFS, suggesting no carry-over effect of stimulation or age-related changes in performance. Occasionally, animals showed a noticeable stimulus-locked alteration of behavior with almost complete cessation of normal activity, appeared lethargic and confused, and were unable to finish the task. These behaviors did not outlast the stimulation. Conclusions: Conclusions: The claustrum appears to be important for sustained attention in rats as bilateral and unilateral electrical stimulation resulted in a decline of performance in a sustained attention task. This suggests that claustral involvement may underly the alteration of consciousness that accompanies epileptic seizures. Funding: This study was made possible by the srartup funds from the George Washington University for MZK.