Figure 3. Human and chimpanzee neural dynamics.

(A) Regional neural dynamics as a function of global recurrent strength ($w$). (B) Violin plot of the distribution of dynamic ranges across brain regions. Each violin shows the first to third quartile range (black line), median (white circle), raw data (dots), and kernel density estimate (outline). $\sigma$ is the standard deviation of the distribution. (C) Spatial organization of dynamic ranges. Data are visualized on inflated cortical surfaces. Light color represents high dynamic range and dark color represents low dynamic range. (D) Violin plot of the distribution of dynamic ranges in seven canonical brain networks. Violin plot details are similar to those in B. (E) Simulated average functional connectivity ($FC$) within the networks in D as a function of $w$. The black line represents the average $FC$ across the whole brain.

Figure 3—figure supplement 1. Confirmatory analysis on individual-specific connectomes and accounting for total brain volume.

(A) Regional neural dynamics as a function of global recurrent strength ($w$) for exemplar human and chimpanzee participants. (B) Violin plot of the standard deviation ($\sigma$) of the distribution of dynamic ranges across brain regions for each participant. Each violin shows the first to third quartile range (black line), median (white circle), raw data (dots), and kernel density estimate (outline). p is the p value of the difference in the mean of the distribution between the species (two-sample t-test). (C) Dynamic range standard deviation ($\sigma$) for each participant as a function of total brain volume. The solid line represents a linear fit with Pearson’s correlation coefficient (r) and p value (p).

Figure 3—figure supplement 2. Confirmatory analysis on human and chimpanzee connectomes of equal connection density.

(A) Regional neural dynamics as a function of global recurrent strength ($w$) for the original human connectome, original chimpanzee connectome, and human connectome pruned to have an equal density as the original chimpanzee connectome. (B) Violin plot of the distribution of dynamic ranges across brain regions. Each violin shows the first to third quartile range (black line), median (white circle), raw data (dots), and kernel density estimate (outline). The data are mean-subtracted for visual purposes. $\sigma$ is the standard deviation of the distribution.

Figure 3—figure supplement 3. Confirmatory analysis accounting for inter-individual variability of connectomic data.

(A) Regional neural dynamics as a function of global recurrent strength ($w$) for the original human connectome, original chimpanzee connectome, and human connectome rescaled to match the inter-individual variability of the original chimpanzee connectome, and chimpanzee connectome rescaled to match the inter-individual variability of the original human connectome. (B) Violin plot of the distribution of dynamic ranges across brain regions. Each violin shows the first to third quartile range (black line), median (white circle), raw data (dots), and kernel density estimate (outline). The data are mean-subtracted for visual purposes. $\sigma$ is the standard deviation of the distribution.

Figure 3—figure supplement 4. Confirmatory analysis on matched sample size.

(A) Regional neural dynamics as a function of global recurrent strength ($w$) for the original human connectome, original chimpanzee connectome, and an exemplar human connectome averaged from a sample of random human participants of the same size as the chimpanzee group (N=22). (B) Violin plot of the distribution of dynamic ranges across brain regions. Each violin shows the first to third quartile range (black line), median (white circle), raw data (dots), and kernel density estimate (outline). The data are mean-subtracted for visual purposes. $\sigma$ is the standard deviation of the distribution. (C) Dynamic range standard deviation ($\sigma$) for multiple random sampling trials of human participants. The solid lines represent the results for the original human and chimpanzee connectomes.

Figure 3—figure supplement 5. Confirmatory analysis accounting for activity propagation delays between brain regions.

(A) Violin plot of the distribution of propagation time delays ($t^d$) across all connections for a representative human and chimpanzee. Each violin shows the first to third quartile range (black line), median (white circle), raw data (dots), and kernel density estimate (outline). (B) Regional neural dynamics as a function of global recurrent strength ($w$). (C) Violin plot of the distribution of dynamic ranges across brain regions. Each violin shows the first to third quartile range (black line), median (white circle), raw data (dots), and kernel density estimate (outline). The data are mean-subtracted for visual purposes. $\sigma$ is the standard deviation of the distribution.

Figure 3—figure supplement 6. Confirmatory analysis accounting for heterogeneous excitatory input across brain regions.

(A) The excitatory input in each brain region $I_j$ is inversely proportional to the rank of its total connection strength ($s_j$). The inset shows the actual relationship between $I_j$ and $s_j$ . (B) Regional neural dynamics as a function of global recurrent strength ($w$). (C) Violin plot of the distribution of dynamic ranges across brain regions. Each violin shows the first to third quartile range (black line), median (white circle), raw data (dots), and kernel density estimate (outline). The data are mean-subtracted for visual purposes. $\sigma$ is the standard deviation of the distribution.

Figure 3—figure supplement 7. Replication of human neural dynamics on an independent dataset.

(A) Regional neural dynamics as a function of global recurrent strength ($w$) for the original human connectome and human connectome obtained from the Human Connectome Project (HCP). (B) Violin plot of the distribution of dynamic ranges across brain regions. Each violin shows the first to third quartile range (black line), median (white circle), raw data (dots), and kernel density estimate (outline). The data are mean-subtracted for visual purposes. $\sigma$ is the standard deviation of the distribution.

Figure 3—figure supplement 8. Replication of human and chimpanzee neural dynamics using a different biophysical model (the Wilson-Cowan model).

(A) Exemplar connectome and schematic diagram of the Wilson-Cowan model. In this biophysical model, each brain region comprises interacting populations of excitatory ($E$) and inhibitory ($I$) neurons. Connections within and between populations are represented by the $w$ parameters; for example, $w_{EE}$ represents the excitatory recurrent connection strength. The excitatory neural population is driven by a constant excitatory input $P_E$ and white noise with standard deviation $D_E$ , while the inhibitory population is only driven by white noise with standard deviation $D_I$ . Regions $i$ and $j$ are connected with weight $A_{ij}$ based on the connectomic data. (B) Regional neural dynamics (mean excitatory firing rate $S_E$) as a function of global excitatory recurrent strength ($w_{EE}$). (C) Violin plot of the distribution of dynamic ranges across brain regions. Each violin shows the first to third quartile range (black line), median (white circle), raw data (dots), and kernel density estimate (outline). The data are mean-subtracted for visual purposes. $\sigma$ is the standard deviation of the distribution.

Figure 3—figure supplement 9. Gradient of dynamic ranges and regional chimpanzee-to-human cortical expansion along the anterior-posterior axis.

(A) Relationship between a brain region’s dynamic range and its anterior-posterior location. The dynamic range values are transformed to z scores. The solid line represents a linear fit with Pearson’s correlation coefficient (r) and p value (p). (B) Relationship between a brain region’s cortical expansion and its anterior-posterior location. The expansion is defined as the human:chimpanzee surface area ratio of each region, following Wei et al., 2019. The solid line represents a linear fit with Pearson’s correlation coefficient (r) and p value (p). The level of expansion is visualized on inflated human cortical surfaces. Light color represents a highly expanded region in humans compared to chimpanzees, while dark color represents a lowly expanded region. (C) Violin plot of the distribution of dynamic ranges of highly expanded anterior regions (top 10 regions) and lowly expanded posterior regions (bottom 10 regions) in the human brain. Each violin shows the first to third quartile range (black line), median (white circle), raw data (dots), and kernel density estimate (outline). p is the p value of the difference in the mean of the distributions (two-sample t-test).

Figure 3—figure supplement 10. Anatomical locations of regions clustered according to seven canonical brain networks.

VIS = Visual; SM = Somatomotor; DA = Dorsal Attention; VA = Ventral Attention; LIM = Limbic; FP = Frontoparietal; DM = Default Mode. These functional networks are mapped onto the 114-region atlas in Supplementary file 1. The networks are visualized on inflated human cortical surfaces.