Abstracts

Rationale: The insular lobe in humans has been associated with cortical representation of viscerosensation, visceral motility, general somatosensation, pain and temperature perception, taste perception, and auditory perception, as well as different types of higher integrative functions (Isnard J et al. Ann Neurol 2000;48:614-623, Augustine JR Brain Res Rev 1996;22:229-244). Even though data from non-human vertebrates as well as functional MRI in humans suggest a qualitative and somatotopic distribution of these functions in the insula, results from electrocortical stimulation of the insula by invasive electrodes in patients with epilepsy have largely failed to corroborate these observations (Penfield W and Faulk ME Brain 1955;78:445-471). We present results of electrocortical stimulation in patients with refractory epilepsy indicating distinct functional representations in the insula. Methods: Four female patients (mean age 35.75 years) with intractable epilepsy underwent evaluation for epilepsy surgery with depth electrodes implanted, among other locations, in one (n=3) or both (n=1) insular lobes. Electrodes with 10 or 12 platinum contacts (Integra Neuroscience®) were inserted in a rostro-caudal direction, therefore sampling the insular cortex in a laminar, rather than radial fashion (Figure 1). Superimposition of presurgical MRI and postsurgical CT (iplan-stereotaxy 2.6®, Brainlab) showed a total of 96 electrode contacts (19.2 per insular lobe) in the anterior (29 contacts), middle (33 contacts) or posterior insula (34 contacts). During invasive video-EEG-monitoring patients underwent stimulation of these contacts (pulse frequency=50 Hz, pulse width=0.5 msec, current intensity=3-14 mA, train duration=3-5 sec). Results: Stimulation of 56 out of 96 contacts (59%) resulted in responses, of which 27 were found to be convincingly reproducible during a separate second stimulation. Elicited phenomena included unspecific and specific somatosensory symptoms, as well as visceral and gustatory sensations (Figure 1). Specific and non-specific somatosensations localized to the posterior-dorsal area of the insula, immediately posterior to where naso-pharyngo-laryngeal sensations and gustation were elicited. Visceral sensations and presumed visceral motility localized to the posterior-ventral areas. Stimulation of the anterior insula remained widely asymptomatic, but elicited complex hallucinations in two single cases in its most anterior part. Conclusions: We find evidence for distinct representations of gustation, viscerosensation, thermal sensation and general somatosensation within the insular cortex by invasive cortical stimulation. This is consistent with neuroanatomical and neurophysiological evidence from studies in non-human vertebrates. These data may contribute to the cartography of cortical representations and may help in recognizing semiologies of insular lobe seizures.