The Variability of Neural Responses to Naturalistic Videos Change with Age and Sex

Neural similarity, measured as the ISC of neural activity, decreased with age. Correlation values ranged from r = –0.58 to r = –0.78, indicating a consistent relationship between maturity and neural variability. ISC was computed for each individual by correlating neural responses from individual subjects with the neural responses from all other subjects for that stimulus (regardless of age and sex).

ISC, a measure of neural similarity, was consistently higher among younger ages and males. A, Across all stimuli, ISC was higher for younger subjects (6–14 yr, light green) than older subjects (15–44 yr, dark green). B, Across all stimuli, ISC was higher for males (blue) than females (red). For both A and B, ISC was computed separately within each age and sex group. Black lines indicate the median.

Sex differences in the young do not exist in the old. Young males were more neurally similar to each other than young females. This sex difference is absent in the older group. Here, ISC was computed within each sex and age group separately and averaged across all stimuli except for Flash and Rest. Black lines indicate the median.

SSVEP magnitude depended on age, but not on sex. A, SSVEP strength was weakly correlated with age across subjects, but it was no different between males and females. B, SSVEP strength was no different between males and females. Black lines indicate the median.

Relationship between ISC magnitude and SSVEP strength. A, SSVEP strength, a measure of the magnitude of evoked responses, correlated with ISC strength, calculated using all stimuli except for Flash and Rest. B, Comparison of ISC strength after SSVEP magnitude was regressed out (ISC – SSVEP) between males and females in the young and old age groups. Although there was a significant difference between the age groups, a difference between the sex groups was not present. Black line indicates the median.

Spatial distributions corresponding to the three strongest components of ISC (C1–C3). Red and blue colors indicate positive and negative correlation of the voltages on the scalp surface with the component activity. These maps are unitless due to an arbitrary scale on the projection vectors. Here, the projections have been computed separately for the combination of the two sex and age groups. As the scalp topographies were relatively consistent across the groups, the differences in ISC across these groups were not due to differences in the spatial topography of correlation within the group.

Eigenvalue spectra of the average covariances for each demographic group. Eigenvalues measure the power of the signal in principal components of the EEG (correlated across time for each stimulus). Each curve is the average eigenvalue spectrum for each group averaged across all stimuli and subjects. A, Young subjects have more power than old subjects in all dimensions. This is represented by the upward shift in their average eigenvalue spectrum. B, The eigenvalue spectrum of females has a shallower slope than that for males, indicating that they have a more diverse set of neural responses.