The cerebral blood flow response dependency on stimulus pulse width is affected by stimulus current amplitude - a study of activation flow coupling

The coupling of cerebral blood flow (CBF) to neuronal activation, referred to as activation flow coupling (AFC), has been a fundamental brain physiology property. The stimulus-evoked CBF response was usually considered as a surrogate marker for neuronal activity in AFC studies. The selection of appropriate stimulation parameters, e.g., current amplitude and pulse width, is of great importance yet the effect of pulse width changes remained contradictory in previous studies. In this work, we use laser speckle contrast imaging (LSCI) to study the spatiotemporal CBF response to hindpaw somatosensory stimulation of different pulse widths (0.3 ms vs 1 ms) and current amplitudes (3 mA vs 6 mA) in a rodent experiment. The results showed that the change of pulse width significantly affected the CBF peak value at a lower current level (p<;0.05). In addition, the duration for observing significantly different average CBF response, denoted as t_d, at various pulse widths, was dependent on stimulus current amplitude. At a lower amplitude (3 mA), t_d was 6.5 s; While at a higher amplitude (6 mA), t_d was 2.5 s. It was indicated that the changes of pulse width had longer influence on the average CBF response at a lower current amplitude. Our findings may help to understand and explain the inconsistent AFC with different stimulation parameters in fundamental brain physiology.