Our
laboratory uses near-infrared light to study two distinct signals the
brain produces during cognitive activity; the Event
Related Optical Signal (EROS), and Near InfraRed Spectroscopy (NIRS).
Optical properties of the brain can be measures by using near-infrared
light (NIR) light which penetrates
several cm inside the head. With appropriate methodologies, it is
possible to focus the measurements to relatively small areas (less than
1 cc) and to distinguish signals from different depths. This yields
very good spatial resolution. Other advantages of these techniques are
safety (because only a very small amount of non-ionizing radiation is
used), relatively low cost, and versatility.
EROS
is based on the measurement of the changes in optical parameters
(scattering and absorption) of active neurons. Some of these changes
occur very rapidly, simultaneously with the electrical activity of the
neurons. For this reason EROS has very good temporal resolution. This
means that EROS can be used to analyze the relative timing of
activity in different areas which in turn reveals information about
functional connections between areas.
This is difficult to study with other brain
imaging methods.
NIRS
is a widely used technique which measures changes in the absorption of
two (or more) wavelengths of light, and allows detection and
quantification of changes in the concentration of oxy and
deoxy-hemoglobin resulting from brain activity. These relatively slow
changes (taking several seconds) are also the basis for fMRI
measurements, but NIRS is able to separately estimate changes in blood
volume and hemoglobin concentration, which fMRI is not able to do.
Because NIRS and EROS measurements can be made simultaneously from the same tissue, they provide unique
opportunities for studying the relation between neuronal activity and
the hemodynamic response.
Current
limitations of EROS include its shallow penetration (~3-4 cm), which
makes it particularly useful for studying cortical (rather than
sub-cortical) activity, and its signal-to-noise ratio, which typically
requires averaging data across a number of subjects. The development of
EROS is one of the major lines of research in our Lab, and has been
funded by the National Institute of Mental Health. Additional relevant
research in this area is conducted at the Laboratory for Fluorescence
Dynamics (LFD, University of California, Irvine), directed by Dr.
Enrico Gratton.
