Multiple parietal operculum subdivisions in humans: Tactile activation maps

Abstract

We focused the present analysis on blood-oxygen-level-dependent responses evoked in four architectonic subdivisions of human posterior parietal operculum (PO) during two groups of tasks involving either vibrotactile stimulation or rubbing different surfaces against the right index finger pad. Activity localized in previously defined parietal opercular subdivisions, OP 1–4, was co-registered to a standard cortical surface-based atlas. Four vibrotactile stimulation tasks involved attention to the parameters of paired vibrations: (1) detect rare target trials when vibration frequencies matched; (2) select the presentation order of the vibration with a higher frequency or (3) longer duration; and (4) divide attention between frequency and duration before selecting stimulus order. Surface stimulation tasks involved various discriminations of different surfaces: (1) smooth surfaces required no discrimination; (2) paired horizontal gratings required determination of the direction of roughness change; (3) paired shapes entailed identifying matched and unmatched shapes; (4) raised letters involved letter recognition. The results showed activity in multiple somatosensory subdivisions bilaterally in human PO that are plausibly homologues of somatosensory areas previously described in animals. All tasks activated OP 1, but in vibrotactile tasks foci were more restricted compared to moving surface tasks. Greater spatial extents of activity especially in OP 1 and 4 when surfaces rubbed the finger pad did not support previously reported somatotopy of the second finger representation in “S2”. The varied activity distributions across OP subdivisions may reflect low-level perceptual and/or cognitive processing differences between tasks.

• Human parietal cortex
• magnetic resonance imaging
• touch

Notes

Notes

1. We computed average z-score maps from the F-test z-scores that were registered to the PALS-B12 surface nodes. The average F-test z-scores per node were assessed with t-tests (Bosch 2000) that were corrected for multiple tests (Bonferroni for 69 328 t-tests based on the number of nodes in the PALS-B12 cortical surface exclusive of the midline) and degrees of freedom (N − 1 varied with sample size (N) per task) at a p-value threshold of 0.01. These corrected t-values were transformed into z-score maps scaled to the same p-value threshold.

2. Error was the subject by task interaction term.