B Yesilyurt

Retinotopic maps and hemodynamic delays in the human visual cortex measured using arterial spin labeling

Cortical representations of the visual field are organized retinotopically, such that nearby neurons have receptive fields at nearby locations in the image. Many studies have used blood oxygenation level-dependent (BOLD) fMRI to non-invasively construct retinotopic maps in humans. The accuracy of the maps depends on the spatial extent of the metabolic and hemodynamic changes induced by the neural activity. Several studies using gradient-echo MRI at 1.5 T and 3T showed that most of the BOLD signal originates from veins, which might lead to a spatial displacement from the actual site of neuronal activation, thus reducing the specificity of the functional localization. In contrast to BOLD signal, cerebral blood flow (CBF) as measured using arterial spin labeling (ASL) is less or not at all affected by remote draining veins, and therefore spatially and temporally more closely linked to the underlying neural activity. In the present study, we determined retinotopic maps in the human brain using CBF as well as using BOLD signal in order to compare their spatial relationship and the temporal delays of each imaging modality for visual areas V1, V2, V3, hV4 and V3AB. We tested the robustness and reproducibility of the maps across different sessions, calculated the overlap as well as signal delay times across visual areas. While area boundaries were relatively well preserved, we found systematic differences of response latencies between CBF and the BOLD signal between areas. In summary, CBF data obtained using ASL allows reliable retinotopic maps to be constructed; this approach is, therefore, suitable for studying visual areas especially in close proximity to large veins where the BOLD signal is spatially inaccurate.

Relationship of the BOLD signal with VEP for ultrashort duration visual stimuli (0.1 to 5 ms) in humans

There is currently a great interest to combine electroencephalography (EEG) and functional magnetic resonance imaging (fMRI) to study brain function. Earlier studies have shown different EEG components to correlate well with the fMRI signal arguing for a complex relationship between both measurements. In this study, using separate EEG and fMRI measurements, we show that (1) 0.1 ms visual stimulation evokes detectable hemodynamic and visual-evoked potential (VEP) responses, (2) the negative VEP deflection at ∼80 ms (N2) co-varies with stimulus duration/intensity such as with blood oxygenation level-dependent (BOLD) response; the positive deflection at ∼120 ms (P2) does not, and (3) although the N2 VEP–BOLD relationship is approximately linear, deviation is evident at the limit of zero N2 VEP. The latter finding argues that, although EEG and fMRI measurements can co-vary, they reflect partially independent processes in the brain tissue. Finally, it is shown that the stimulus-induced impulse response function (IRF) at 0.1 ms and the intrinsic IRF during rest have different temporal dynamics, possibly due to predominance of neuromodulation during rest as compared with neurotransmission during stimulation. These results extend earlier findings regarding VEP–BOLD coupling and highlight the component- and context-dependency of the relationship between evoked potentials and hemodynamic responses.

BOLD Response in Lateral Geniculate Nucleus (LGN) at Very Short Stimulus Durations

On the functional anatomy of intrinsic, phasic and self-induced alertness. Temporal changes in neural activation underlying cognitive learning processes in patients with schizophrenia: An fMRI study. The angular gyrus is equally involved in different aspects of action awareness. ERP and fMRI correlates of endogenous and exogenous mechanisms of spatial selective attention. Sustained attention in healthy siblings of schizophrenic patients: an event-related functional magnetic resonance study. A relevant analysis of task difficulty and brain activity during meter inspection: an fMRI study.

The Dynamics of ERP and Hemodynamic Responses at Very Short Stimulus Durations

CONTENTS Welcome Remarks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . S3 General Information: Registration, Social Events, Speaker Ready Room, Internet Café . . . . . . . . . . . . . . . . . . . S4 Sunday, June 10: Educational Courses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . S6 Basic fMRI Course . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . S6 Advanced fMRI Course . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . S7 Advanced MEG/EEG Course . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . S8 Cognitive Neuroscience Course . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . S10 Structural Brain Mapping Course . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . S11 Opening Ceremony . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . S12 Monday, June 11 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . S13 Tuesday, June 12 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . S19 Wednesday, June 13. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . S25 Thursday, June 14 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . S31 Schedule of Poster Presentations and List of Posters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . S36 Author Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . S126 Exhibitor List . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . S156 Scientific Posters and Exhibitor Floor Plans . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . S160 Sheraton Floor Plans . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . S161 Council and Committees . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . S162 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . S163 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . S167 Abstract Review Committee .

Hemodynamic Response to 0,1 ms (at 7T) and 1 ms (at 3T) Stimulus is Detectable in Human Subjects

This journal suppl. entitled: Twelfth Annual Meeting of the Organization for Human Brain Mapping, Florence, Italy, 11–15 June 2006