Functional Mapping of Nervous System Using Optical Imaging Techniques

Functional mapping techniques including functional magnetic resonance imaging (fMRI), positron emission tomography (PET), and magnetoencephalography (MEG) can be used to study the function of the nervous system. Optical imaging is an emerging technique for functional imaging of the nervous tissue. Functional optical imaging can be classified into two major streams; intrinsic signal optical imaging (ISO) and voltage-sensitive dye optical imaging (VDO). ISO is related to hemodynamic changes such as hemoglobin concentration and oxygenation changes, cytochrome oxidation change, and light scattering. On the contrary, VOD measures changes in membrane potentials of neural cells. Therefore, ISO reflects metabolic activity of neurons, while VOD directly reflects neural activity. Recent advances in optical imaging opened the possibility of its application to clinical situations as well as basic researches. Further, development of optical imaging may greatly contribute to the understanding of the function of the nervous system.

Complex, multifocal, individual-specific attention-related cortical functional circuits

Recent studies focusing on the analysis of individual patterns of non-sensory-motor CNS activity may significantly alter our view of CNS functional mapping. We have recently provided evidence for highly variable attention-related Slow Potential (SP) generating cortical areas across individuals (Basile et al., 2003, 2006). In this work, we present new evidence, searching for other physiological indexes of attention by a new use of a well established method, for individual-specific sets of cortical areas active during expecting attention. We applied latency corrected peak averaging to oscillatory bursts, from 124-channel EEG recordings, and modeled their generators by current density reconstruction. We first computed event-related total power, and averaging was based on individual patterns of narrow task-induced band-power. This method is sensitive to activity out of synchrony with stimuli, and may detect task-related changes missed by regular Event-Related Potential (ERP) averaging. We additionally analyzed overall inter-electrode phase-coherence. The main results were (1) the detection of two bands of attention-induced beta range oscillations (around 25 and 21 Hz), whose scalp topography and current density cortical distribution were complex multi-focal, and highly variable across subjects, including prefrontal and posterior cortical areas. Most important, however, was the observation that (2) the generators of task-induced oscillations are largely the same individual-specific sets of cortical areas active during the resting, baseline state. We concluded that attention-related electrical cortical activity is highly individual-specific (significantly different from sensory-related visual evoked potentials or delta and theta induced band-power), and to a great extent already established during mere wakefulness. We discuss the critical implications of those results, in combination with other studies presenting individual data, to functional...

Surgical Treatment of the Occipital Lobe Epilepsy

PURPOSE: Although occipital lobe epilepsy may be operable, localization of the epileptogenic zone can be difficult and there is a high risk of postoperative visual loss. METHODS: Thirteen patients with intractable occipital lobe epilepsy underwent resective surgery. Preoperatively, all underwent video-EEG monitoring using extracranial electrodes and MRI; Nine had PET scans; In ten, who were cortically stimulated with subdural grid electrodes, invasive recordings were made. Foramen ovale electrodes had been previously used in two, and bitemporal depth electrodes in one; Nitemporal and occipital electrodes had been used in one, and a unilateral temporal depth electrode in one. Nine underwent partial occipital resection, which had spared the nonepileptogenic primary visual cortex, and two underwent a total unilateral occipital lobectomy: A temporal lobectomy was performed in two. RESULTS: Twelve patients experienced visual aura prior to complex partial seizure, and five had quadrantanopsia. In no patient was noninvasive monitoring reliable in localizing the epileptogenic zone, and in eleven patients, this was localized by invasive recordings. Electrocortical stimulation with subdural grid electrodes evoked simple and complex visual phenomena in nine patients, reproduced the same auras in four, induced a typical seizure in two, and provided language mapping in five. Histopathologic findings revealed cortical dysplasia in five; Tuberous sclerosis was combined in one, hamartoma and ganglioglioma, each in two, and infarction and nonspecific change in the occipital lobe each in one, neuronal loss in the hippocampus and neuronal heterotopia in mesial temporal structures were reported in two patients who underwent temporal lobectomy. Ten were seizure-free during follow-up between six and 46(mean 22.3) months. Seizures recurred in two and were unchanged in one. Only two patients with preoperative quadrantanopsia developed homonymous hemianopsia. CONCLUSION: This study suggests that in the surgical treatment of the occipital lobe epilepsy, the use of intracranial EEG and functional mapping with subdural grid electrodes, can achieve a good outcome, including the preservation of vision.