A travelling wave paradigm, involving digit movements in a set sequence, was used to capture digit preference and the smooth progression of adjacent digit representations in primary somatosensory cortex. (A) The travelling wave task involved 8 repeated cycles of continuous individual digit movements. Each 45 s cycle consisted of five 9 s blocks dedicated to each digit (as exemplified by the coloured squares), with each run cycling through either D1-D2-D3-D4-D5 (forward, top) or D5-D4-D3-D2-D1 (backward, bottom). Each of the forward and backward runs was repeated twice. The numbers 1–5 and colours correspond to the five digits, as visualised in the right side of the panel. (B) Preprocessed BOLD time courses from individual voxels (the example time course of one voxel is shown in red) were cross-correlated against a reference model. The model corresponded to a single-digit movement (9 s ‘on’, 36 s ‘off’- the period of movement of all other digits), and was systematically shifted in time to model activity throughout a full cycle (30 shifts, corresponding to the 30 lags of the 45 s cycle). The figure shows three different model lags (1, 12 and 24), resulting in varying cross-correlation outcomes. Lag 24 was the optimal model lag for this preprocessed BOLD time course. (C) The standardised r-values (Fisher’s r-to-z, y-axis) resulting from the cross-correlation were plotted as a function of lag (x-axis) for each individual voxel in each run. In the left panel, cross-correlation values from the example voxel shown in B are plotted for each of the four runs. The optimal fit for the voxel is demonstrated by the peak cross-correlation (digit 1, in the left panel; digit 2 in the right panel, taken from separate voxels). Lags associated with the same digits were averaged, first within and then across runs. A winner-take-all approach was used to determine digit preference, based on the highest average r-value, resulting in five separate digit maps. False discovery rate (FDR) was applied for each of these single digit maps to adjust the threshold based on the criterion q (FDR) < 0.05. (D) Each of the five digits was assigned a colour code, as demonstrated on the left. The five digit maps were projected to the cortical surface, to display digit preference maps. Note that no masking was applied when presenting the resulting maps. Within the resulting five-digit map a gradient of progression across digits was visualised, based on the voxel-wise r-values for each of the 30 lags. The resulting map was located in the central sulcus and postcentral gyrus, corresponding to the primary somatosensory cortex, around the anatomical hand knob.