Noninvasive optical imaging in the visual cortex in young infants

Abstract

During the developmental stage, the brain undergoes anatomic, functional, and metabolic changes necessary to support the complex adaptive behavior of a mature individual. Estimation 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 providing useful information on structure-function relationships in both normal and disease states. We used multichannel near-infrared spectroscopy (MNIRS), a new noninvasive imaging technique for revealing the course of neural activity in selected brain regions, to monitor the activities of the visual cortex as mirrored by hemodynamic responses in infants subjected to photostimulation during natural sleep. In the infants, oxyhemoglobin and total hemoglobin decreased and deoxyhemoglobin increased in the visual cortex with photostimulation. This pattern of responses was different from the response pattern in adults reported previously. The different patterns of responses to photostimulation in the visual cortices of infants and adults might reflect developmental and behavioral differences. It may reflect a different functional organization of the visual cortex in infants or ongoing retinal development. Our results demonstrated that regional hemodynamic change could be detected in a small area around the visual cortex. MNIRS offers considerable potential for research and noninvasive clinical applications.

Figure 1

A: Measurement positions on the head of an infant. The probe was placed over the bilateral occipital region, with the center of probe at the inion. B: Measurement positions and coordinate system. Open circles, light incident positions; closed circles, detector positions; squares, measurement positions.

Figure 2

Grand averages of changes in [oxyHb], [deoxyHb], and [totalHb] as a function of time at all 24 channels from 10 trials in an infant case (MY). Photostimulation was induced for a period of 15 sec (from 15 to 30 sec).

Figure 3

Dynamic 2D images of [oxyHb], [deoxyHb] and [totalHb] in an infant aged 111 days (43 wks postconception) (A) and an adult volunteer (B). Images were taken at 5‐sec intervals from 0–25 sec after the start of photostimulation. Photostimulation was induced for a period of 15 sec.

Figure 4

Grand averages of changes in [oxyHb] as a function of time in the same subjects as those for whom results are shown in Figure 3. From the 24 source‐detector signals, the signal with the greatest change in [oxyHb] in each subject was selected for statistical analysis. A: Average from 10 trials in an infant. B: Average from eight trials in an adult. The arrow indicates the 15‐sec period of visual flashlight stimulation. Changes in [oxyHb], [deoxyHb] and [totalHb] are given in mM · cm. The data were obtained every 130 msec and averaged for 1 sec. Error bars = SD of the mean. *Significance of mean concentration changes from 5 sec before the start of photostimulation (Wilcoxon's signed‐rank test; *P < 0.05).

Figure 5

Dynamic 2D images of [oxyHb], [deoxyHb], and [totalHb] in all five infants (A) and five adult volunteers (B). Images were taken at the time when the [oxyHb] signal reached to minimum or maximum value in the channel showing the signal with the greatest changes in [oxyHb] from among the 24 channels.