Brain auditory activation measured by near-infrared spectroscopy (NIRS) in neonates

This study presents a new measure of the hemodynamic changes to an auditory stimulus in newborns. Nineteen newborns born at 28-41 wk and aged 1 to 49 d were studied in waking and/or sleeping state, for a median time of 4 min 40 s before, 2 min 40 s during, and 3 min 5 s after an acustic stimulus (tonal sweep of frequency increasing from 2 to 4 kHz, intensity 90 dB SPL) originating 5 cm from the external auditory meatus. The emitter and detector optodes were placed over the left or right temporal region, corresponding to T3 or T4 EEG electrodes. The concentration changes in cerebral chromophores D[HbO2], D[Hb] and Doxidized-reduced cytochrome aa3 were recorded every 5 s. Changes in cerebral blood volume were calculated from the changes in total Hb 3 0.89/large vessel Hb concentration. Increased oxyhemoglobin, D[HbO2], total Hb, D[Hb sum], and cerebral blood volume, DCBV, were found in 13/19 neonates, with the exception of a neonate who only had increased in D[Hb], D[Hb sum] and DCBV. During the stimulation phase there was a significant increase in DCBV (t test, p 5 0.00006) in the responsive newborns from a mean value of 0.006 (60.02) mL/ 100 g in the pretest phase to 0.09 (60.06) mL/100 g during the auditory stimulus. After the test DCBV decreased to 0.04 (60.07) mL/100 g (t test, p 5 0.01), so did D[Hb sum] (p 5 0.02). Hemodynamic responses of the subjects who showed increases in D[Hb sum] and D[HbO2] were analyzed to study the D[Hb]. The responder subjects could be classified into two groups according to D[Hb] changes: 8/13 (61.5%) showed an increase of D[Hb] (pattern A), while 5/13 (38.4%) showed a decrease (pattern B) (t test, p 5 0.03). These two patterns did not show differences related to D[HbO2] and D[Hb sum]. The DCBV changes in nonresponders presented a decrease during the test phase (t test, p 5 0.04). CBV did not return to pretest values, suggesting a fronto-temporal brain pathway for storing unusual sounds. The increase in CBV followed the local increase in oxyhemoglobin and total Hb concentrations due to a greater use of oxygen in the homolateral temporal cortex of the newborns.