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Noninvasive recording of fast optical signals presumably reflecting neuronal activity is a challenging task because of a relatively low signal-to-noise ratio. To improve detection of those signals in rapid object recognition tasks, we used the Independent Component Analysis (ICA) to reduce “global interference” (heartbeat and contribution of superficial layers). We recorded optical signals from the left prefrontal cortex in 10 right-handed participants with a continuous-wave instrument (DYNOT, NIRx, Brooklyn, NY). Visual stimuli were pictures of urban, landscape and seashore scenes with various vehicles as targets (target-to-non-target ratio 1:6) presented at ISI = 166 ms or 250 ms. Subjects mentally counted targets. Data were filtered at 2–30 Hz and artifactual components were identified visually (for heartbeat) and using the ICA weight matrix (for superficial layers). Optical signals were restored from the ICA components with artifactual components removed and then averaged over target and non-target epochs. After ICA processing, the event-related response was detected in 70–100% of subjects. The refined signal showed a significant decrease from baseline within 200–300 ms after targets and a slight increase after non-targets. The temporal profile of the optical signal corresponded well to the profile of a “differential ERP response”, the difference between targets and non-targets which peaks at 200 ms in similar object detection tasks. These results demonstrate that the detection of fast optical responses with continuous-wave instruments can be improved through the ICA method capable to remove noise, global interference and the activity of superficial layers. Fast optical signals may provide further information on brain processing during higher-order cognitive tasks such as rapid categorization of objects.

Abstract. Near-infrared spectroscopy is a novel imaging technique potentially sensitive to both brain hemodynamics (slow signal) and neuronal activity (fast optical signal, FOS). The big challenge of measuring FOS noninvasively lies in the presumably low signal-to-noise ratio. Thus, detectability of the FOS has been controversially discussed. We present reliable detection of FOS from 11 individuals concurrently with electroencephalogram (EEG) during a Go-NoGo task. Probes were placed bilaterally over prefrontal cortex. Independent component analysis (ICA) was used for artifact removal. Correlation coefficient in the best correlated FOS-EEG ICA pairs was highly significant (p < 10 − 8 ), and event-related optical signal (EROS) was found in all subjects. Several EROS components were similar to the event-related potential (ERP) components. The most robust "optical N200" at t = 225 ms coincided with the N200 ERP; both signals showed significant difference between targets and nontargets, and their timing correlated with subject's reaction time. Correlation between FOS and EEG even in single trials provides further evidence that at least some FOS components "reflect" electrical brain processes directly. The data provide evidence for the early involvement of prefrontal cortex in rapid object recognition. EROS is highly localized and can provide cost-effective imaging tools for cortical mapping of cognitive processes. C 2010 Society of Photo-Optical Instrumentation Engineers.

Near-infrared spectroscopy (NIRS) is a developing technology for low-cost noninvasive functional brain imaging. With multichannel optical instruments, it becomes possible to measure not only local changes in hemoglobin concentrations but also temporal correlations of those changes in different brain regions which gives an optical analog of functional connectivity traditionally measured by fMRI. We recorded hemodynamic activity during the Go-NoGo task from 11 right-handed subjects with probes placed bilaterally over prefrontal areas. Subjects were detecting animals as targets in natural scenes pressing a mouse button. Data were low-pass filtered<1 Hz and cardiac∕respiration∕superficial layers artifacts were removed using Independent Component Analysis. Fisher's transformed correlations of poststimulus responses (30 s) were averaged over groups of channels unilaterally in each hemisphere (intrahemispheric connectivity) and the corresponding channels between hemispheres (interhemispheric connectivity). The hemodynamic response showed task-related activation (an increase∕decrease in oxygenated∕deoxygenated hemoglobin, respectively) greater in the right versus left hemisphere. Intra- and interhemispheric functional connectivity was also significantly stronger during the task compared to baseline. Functional connectivity between the inferior and the middle frontal regions was significantly stronger in the right hemisphere. Our results demonstrate that optical methods can be used to detect transient changes in functional connectivity during rapid cognitive processes.

A 3D marine seismic survey of the Odoptu license area off northeastern Sakhalin Island, Russia, was conducted by DalMorNefteGeofizika (DMNG) on behalf of Exxon Neftegas Limited and the Sakhalin-1 consortium during mid-August through early September 2001. The key environmental issue identified in an environmental impact assessment was protection of the critically endangered western gray whale ( Eschrichtius robustus ), which spends the summer–fall open water period feeding off northeast Sakhalin Island in close proximity to the seismic survey area. Seismic mitigation and monitoring guidelines and recommendations were developed and implemented to reduce impacts on the feeding activity of western gray whales. Results of the acoustic monitoring program indicated that the noise monitoring and mitigation program was successful in reducing exposure of feeding western gray whales to seismic noise.