Abstracts

Rationale: The claustrum is a thin layer of grey matter that is separated from the insula by the extreme capsule and from the putamen by the external capsule. The function of the claustrum is unknown, although animal studies have demonstrated bidirectional connectivity between the claustrum and all neocortical regions. This extensive connectivity suggests a role in binding visual, somatosensory, auditory, and motor information, and it has been suggested that the claustrum plays a main role in integration of conscious percepts (Crick & Koch 2004). Electrical stimulation of the claustrum in cats results in a behavioral arrest and unresponsiveness, similar to the alteration of awareness that accompanies some seizures in humans (Gobar 1964). Here, we present the results of electrical stimulation of the claustrum in humans. Methods: A 58-year-old woman presented with intractable complex partial epilepsy and olfactory auras. Her non-invasive video-EEG monitoring confirmed left hemispheric seizure onset. She then underwent invasive monitoring with depth electrodes for identification of the seizure focus, including a 12-contact depth electrode that sampled the left insula and claustrum. Scalp electrodes were also added. She underwent electrocortical stimulation mapping at 50-Hz with current intensities reaching 18 mA. Results: Stimulation of the claustrum at currents 8 mA or higher resulted in a behavioral arrest, blank staring, and unresponsiveness with reduction of spontaneous respiratory movements. This effect was consistently reproducible. The patient returned to her baseline as soon as the stimulation stopped with no recollection of the stimulation period. Her symptoms during stimulation could not be attributed to negative motor phenomena or aphasia. She was able to continue repetitive movements with her tongue and hands during stimulation if initiated before the stimulus train. Similarly, if she started to say a word repeatedly before stimulation, she could continue the task through stimulation, although with some dysarthria. No seizures or after discharges were seen on her depth electrode or scalp EEG. Stimulation of the Insula or the white matter surrounding the claustrum did not elicit any changes. Conclusions: Our findings indicate that the claustrum is an essential part of the neuronal network that controls awareness and suggest that involvement of the claustrum may explain the alteration of awareness typical of temporal lobe seizures. In addition, absence seizures may be associated with bilateral claustral involvement as suggested by EEG-fMRI studies that found increased activation in the insulae and claustrums during idiopathic generalized epileptiform discharges (Gotman et al., 2005; Liu et al., 2008).