Introduction
During development, the brain undergoes sequential anatomical, functional, and organizational changes necessary to support the complex adaptive behavior of a mature normal individual. Delineation of developmental changes occurring in different regions of the brain would provide a means of relating various behavioral phenomena to maturation-specific brain structures, thereby enhancing our understanding of structure-function relationships in both normal and disease states. NIRS is a noninvasive method for detecting changes in the concentrations of oxyHb and deoxyHb at the bedside, and it has been used to study functional activation of various areas of the brain. In this study, we used to use NIRS to monitor the activities of the visual cortex as mirrored by hemodynamic responses in newborns subjected to photostimulation during natural sleep, and we compared them with normal adult response patterns.
Patients and Methods
We examined five infants, aged 3 d to 2 wk, and five healthy adult volunteers using multichannel NIRS. Informed consent in writing was obtained from the parents of the infants and from the adult volunteers, and the protocol was approved by the local ethics committee. A probe consisting of 16 optical fibers, 8 for transmission and 8 for detection, was placed over the bilateral occipital region, with the center of probe at the level of the calcarine sulcus. The interoptode distance was 3 cm for adults and 2 cm for infants. Measurements in the infants were performed in the spine or prone position with the occipital region of the head touching the probe, and measurements were performed in the adults in a comfortable sitting position in a dark, quiet room. The subjects were exposed to stroboscopic white flashing light at 8 Hz projected on the eyelids during the stimulation period (15 seconds) and to non-flashing light during the rest period (45 seconds). The stimulation cycle was repeated 11 to 30 times.
Results
In the adult subjects, as was shown previously, [oxyHb] and [totalHb] in the visual cortex increased with the photostimulation. In the neonates, on the other hand, [oxyHb] and [totalHb] in the visual cortex decreased and [deoxyHb] increased with photostimulation. There were no significant changes in any of these parameters in the no stimulation control group. The different response patterns to photostimulation in the visual cortices in neonates and adults might reflect developmental and behavioral differences. Its may reflect a different functional organization of the visual cortex in neonates or the on-going retinal development.
Conclusion
We have reported NIRS measurement of functional hemodynamic responses in infants during natural sleep. The NIRS signal response patterns in neonates and adults are different. This difference may reflect differences in the behavioral or developmental state.