The development of neural inhibition across species: insights from the Hurst exponent

The maturation of inhibitory neurons is crucial for regulating plasticity in developing brains. Previous work has suggested that the Hurst exponent, the measure of autocorrelation in time series, reflects inhibition, but empirical data supporting this link is sparse. Here, we demonstrate significant spatial correlations between the Hurst exponent and ex vivo parvalbumin inhibitory mRNA expression in human children and adults, as well as between the Hurst exponent and parvalbumin-positive cell counts in mice, across both sexes. We further identified developmental plateaus in inhibition, as indicated by both parvalbumin inhibitory mRNA expression and the Hurst exponent, occurring prior to adolescence in humans and rats. In sum, this work suggests that the Hurst exponent can be used to study the development of inhibition in vivo, and to understand inhibitory development across species. Significance Statement Understanding the spatial and temporal progression of developmental plasticity is crucial for identifying periods of vulnerability and opportunity in the human brain. This study supports the Hurst exponent as a promising in vivo marker for inhibition, showing significant spatial correlations with parvalbumin RNA expression and cell counts across species. Findings indicate a plateau in inhibition by late childhood in humans and prior to puberty in rats, suggesting the Hurst exponent's translational potential for exploring inhibitory development mechanisms in both humans and animals.