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

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 (to nal sweep of frequency increasing from 2 to 4 kHz, intensity 90 dB SPL) ori ginating 5 cm from the external auditory meatus. The emitter and detector o ptodes were placed over the left or right temporal region, corresponding to T3 or T3 EEG electrodes. The concentration changes in cerebral chromophore s Delta [HbO2], Delta [Hb] and Delta oxidized-reduced cytochrome aa, were r ecorded every 5 s. Changes in cerebral blood volume were calculated from th e changes in total Hb x 0.89/large vessel Hb concentration. Increased oxyhe moglobin, Delta [HbO2], total Hb, Delta [Hb (sum)], and cerebral blood volu me, Delta CBV, were found in 13/19 neonates, with the exception of a neonat e who only had increased in Delta [Hb], Delta [Hb (sum)] and Delta CBV. Dur ing the stimulation phase there was a significant increase in Delta CBV (t test, p = 0.00006) in the responsive newborns from a mean value of 0.006 (/-0.02) mL/100 g in the pretest phase to 0.09 (+/-0.06) mL/100 g during the auditory stimulus. After the test Delta CBV decreased to 0.04 (+/-0.07) mL /100 g (t test, p = 0.01), so did Delta [Hb(sum)] (p = 0.02). Hemodynamic r esponses of the subjects who showed increases in Delta [Hb (sum)] and Delta [HbO(2)] were analyzed to study the Delta [Hb]. The responder subjects cou ld be classified into two groups according to Delta [Hb] changes: 8/13 (61. 5%) showed an increase of Delta [Hb] (pattern A), while 5/13 (38.4%) showed a decrease (pat tem B) (t test, p = 0.03). These two patterns did not show differences related to Delta [HbO(2)] and Delta [Hb (sum)]. The Delta CBV changes in nonresponders presented a decrease during the test phase (t test , p = 0.04). CBV did not return to pretest values, suggesting a fronto-temp oral brain pathway for storing unusual sounds. The increase in CBV followed the local increase in oxyhemoglobin and total Hb concentrations due to a g reater use of oxygen in the homolateral temporal cortex of the newborns.