Figure 1.
Brain regions activated during speech and action observation, tool-use, word generation, and Acheulean knapping.
S = speech observation, A = action observation, T = planning tool use, W = word generation, K = Acheulean knapping. The table shows potential overlap in the neural networks used in all five tasks. The posterior temporal cortex is used exclusively for observation. Fronto-parietal brain areas activated by both cued word generation and knapping are highlighted in orange. Cortical areas supplied by the MCA (middle cerebral artery) are highlighted in green (left hemisphere) and red (right hemisphere).
Figure 2.
fTCD recording during the knapping task.
A participant in our study carrying out the knapping task during fTCD recording. Two small, head-mounted probes measure cerebral blood flow velocities. The inset shows a diagram of the middle cerebral arteries that were insonated in our study.
Figure 3.
Stone tools produced in the experiment.
Three handaxes produced by three participants in the experiment. Front, back, and side views are shown for each handaxe.
Figure 4.
Bilateral CBFV changes during cued word generation and Acheulean tool-making.
Bilateral CBFV changes were recorded simultaneously in the left (black trace) and right (red) MCAs for the language (A) and knapping (B) tasks. During the language task, blood flow in the left hemisphere increases more strongly than on the right, while the flint knapping task causes blood flow in the right artery to increase more than on the left. Blood flow changes are measured relative to a baseline, marked by a black bar (B-line), covering the mean CBFV over the final 5 seconds before task onset.
Figure 5.
Brain blood flow volume lateralization changes for cued word generation and Acheulean tool-making.
Raw mean CBFV (cerebral blood flow volume) difference (ΔV) over time during the language and knapping tasks. Positive values indicate a left dominant blood flow lateralization; negative values indicate greater blood flow on the right. The upper line shows the language task; the lower line shows the stone knapping task. The shaded areas show the SEM (standard error of the mean) at each data point.
Figure 6.
Correlation analysis of relative brain blood flow volume changes during language and knapping.
The top panel shows the correlation between the mean CBFV differences (ΔV) for both tasks over a moving 5-second analysis windows. The x value represents the delay of the analysis window relative to the interval onset. Horizontal lines show uncorrected significance thresholds for the correlations. Bottom panels show individual subject data; the two left-handed subjects are represented by filled circles. The lines are linear fits. Window A covers 2–7 s after onset. Window B covers 10–15 s after onset.