The event-related optical signal: a new tool for studying brain function (original) (raw)
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Shedding light on brain function: the event-related optical signal
2001
A new brain imaging technique, the event-related optical signal (EROS), combines spatial resolution of better than a centimetre with temporal resolution of the order of milliseconds, which makes it ideal to study the time course of neural activity in localized cortical areas. The imaging signal reflects changes in the optical scattering properties of brain tissue that are concurrent with neuronal activity. Because the same instrument that measures EROS can also detect hemodynamic phenomena that occur subsequent to neuronal activity, this technique is uniquely suited to study the relationship between neuronal and vascular effects (neurovascular coupling). Presently, limitations of the technique include reduced penetration (so that only structures within 3-5 cm from the surface of the head can be studied) and relatively low signal-to-noise ratio, which in reality requires that data is averaged across subjects.
Fast and Localized Event-Related Optical Signals (EROS) in the Human Occipital …
Neuroimage
Localized evoked activity of the human cortex produces fast changes in optical properties that can be detected noninvasively (event-related optical signal, or EROS). In the present study a fast EROS response (latency E100 ms) elicited in the occipital cortex by visual stimuli showed spatial congruence with fMRI signals and temporal correspondence with VEPs, thus combining subcentimeter spatial localization with subsecond temporal resolution. fMRI signals were recorded from striate and extrastriate cortex. Both areas showed EROS peaks, but at different latencies after stimulation (100 and 200-300 ms, respectively). These results suggest that EROS manifests localized neuronal activity associated with information processing. The temporal resolution and spatial localization of this signal make it a promising tool for studying the time course of activity in localized brain areas and for bridging the gap between electrical and hemodynamic imaging methods. 1997 Academic Press Key Words: noninvasive optical imaging; eventrelated optical signal (EROS); fMRI; VEPs; functional brain mapping; photon migration in tissues.
Neuroimage, 2000
The event-related optical signal (EROS) has been recently proposed as a method for studying noninvasively the time course of activity in localized cortical areas (G. Gratton and M. Fabiani, 1998, Psychonomic Bull. Rev. 5: 535-563). Previous data have shown that EROS has very good temporal resolution and can provide detailed surface activity maps. In the present study we investigated whether the depth of the active area can also be estimated. Nine subjects were run in a study in which the eccentricity of the visual stimuli was varied, and EROS was recorded from medial occipital areas using multiple source-detector distances. Seven of the same subjects were also run through a functional magnetic resonance imaging (fMRI) study using the same protocol. The fMRI data indicated that the depth from the head surface to the cortical area activated increased systematically with the eccentricity of the visual stimuli. The EROS recording indicated a response with a latency of 60 -80 ms from stimulation. This response varied systematically with eccentricity, so that the greater the eccentricity of the stimuli, the longer the source-detector distance (and thus the depth) at which the EROS effect was observed. The depth of the brain area generating the EROS effect was estimated using a simple algorithm derived from phantom studies on homogeneous media. The average depth estimates for each eccentricity condition obtained with EROS corresponded with those obtained with fMRI, with discrepancies of less than 1 mm. These data demonstrate that multiple source-detector distances can be used to estimate the depth of the cortical areas responsible for the EROS effects.
Fast optical imaging of human brain function
2010
Great advancements in brain imaging during the last few decades have opened a large number of new possibilities for neuroscientists. The most dominant methodologies (electrophysiological and magnetic resonance-based methods) emphasize temporal and spatial information, respectively. However, theorizing about brain function has recently emphasized the importance of rapid (within 100 ms or so) interactions between different elements of complex neuronal networks. Fast optical imaging, and in particular the event-related optical signal (EROS, a technology that has emerged over the last 15 years) may provide descriptions of localized (to sub-cm level) brain activity with a temporal resolution of less than 100 ms. The main limitations of EROS are its limited penetration, which allows us to image cortical structures not deeper than 3 cm from the surface of the head, and its low signal-to-noise ratio. Advantages include the fact that EROS is compatible with most other imaging methods, including electrophysiological, magnetic resonance, and trans-cranial magnetic stimulation techniques, with which can be recorded concurrently. In this paper we present a summary of the research that has been conducted so far on fast optical imaging, including evidence for the possibility of recording neuronal signals with this method, the properties of the signals, and various examples of applications to the study of human cognitive neuroscience. Extant issues, controversies, and possible future developments are also discussed.
Non-invasive optical spectroscopy and imaging of human brain function
Trends in Neurosciences, 1997
Brain activity is associated with changes in optical properties of brain tissue. Optical measurements during brain activation can assess haemoglobin oxygenation, cytochrome-c-oxidase redox state, and two types of changes in light scattering reflecting either membrane potential (fast signal) or cell swelling (slow signal), respectively. In previous studies of exposed brain tissue, optical imaging of brain activity has been achieved at high temporal and microscopical spatial resolution. Now, using near-infrared light that can penetrate biological tissue reasonably well, it has become possible to assess brain activity in human subjects through the intact skull non-invasively. After early studies employing single-site near-infrared spectroscopy, first near-infrared imaging devices are being applied successfully for low-resolution functional brain imaging. Advantages of the optical methods include biochemical specificity, a temporal resolution in the millisecond range, the potential of measuring intracellular and intravascular events simultaneously and the portability of the devices enabling bedside examinations.
Neuroimage, 1997
Localized evoked activity of the human cortex produces fast changes in optical properties that can be detected noninvasively (event-related optical signal, or EROS). In the present study a fast EROS response (latency E100 ms) elicited in the occipital cortex by visual stimuli showed spatial congruence with fMRI signals and temporal correspondence with VEPs, thus combining subcentimeter spatial localization with subsecond temporal resolution. fMRI signals were recorded from striate and extrastriate cortex. Both areas showed EROS peaks, but at different latencies after stimulation (100 and 200-300 ms, respectively). These results suggest that EROS manifests localized neuronal activity associated with information processing. The temporal resolution and spatial localization of this signal make it a promising tool for studying the time course of activity in localized brain areas and for bridging the gap between electrical and hemodynamic imaging methods. 1997 Academic Press Key Words: noninvasive optical imaging; eventrelated optical signal (EROS); fMRI; VEPs; functional brain mapping; photon migration in tissues.
Noninvasive near infrared optical imaging of human brain function with subsecond temporal resolution
Õ ur understanding of human brain function can clearly benefit from neurophysiological techniques capable of providing dynamic maps of activity. A series of studies is reviewed indicating that noninvasive nearinfrared optical imaging methods can provide a unique combination of spatial and temporal resolution that could be used to derive dynamic maps of human brain activity. The noninvasive NIR optical data reviewed are based on the frequency-domain time-resolved measurement of photon migration parameters (intensity and delay) through brain tissue. These measurements are taken through the intact surface of the head. With these methods, two distinct components of the optical response can be identified: the "slow optical signal" (2-10 s latency), presumably due to hemodynamic and metabolic changes, and the "fast optical signal" (or event-related optical response) occurring as early as 50 to 100 ms from stimulation, and probably due to neuronal activation. @ 1996 Society of Photo-Optical Instrumentation Engineers.
Brain Science Advances
The present work describes the use of noninvasive diffuse optical tomography (DOT) technology to measure hemodynamic changes, providing relevant information which helps to understand the basis of neurophysiology in the human brain. Advantages such as portability, direct measurements of hemoglobin state, temporal resolution, non‐restricted movements as occurs in magnetic resonance imaging (MRI) devices mean that DOT technology can be used in research and clinical fields. In this review we covered the neurophysiology, physical principles underlying optical imaging during tissue‐light interactions, and technology commonly used during the construction of a DOT device including the source‐detector requirements to improve the image quality. DOT provides 3D cerebral activation images due to complex mathematical models which describe the light propagation inside the tissue head. Moreover, we describe briefly the use of Bayesian methods for raw DOT data filtering as an alternative to linear ...