Cortical network for vibrotactile attention: a fMRI study

Abstract

We used fMRI to identify brain areas activated during tactile attention tasks. Participants detected the interval containing target stimulation of higher vibrotactile frequency or longer duration. Attributes were selectively or neutrally cued. A control backwards-counting task included concurrent, but irrelevant corresponding vibrotactile stimulation. Group analyses of average F-statistic maps, participant conjunction maps, and estimated time courses utilized data mapped to a standard average surface atlas (PALS B12). Repeated-measures, random-effects MANOVA examined blood oxygenation level-dependent (BOLD) signal modulation differences amongst tasks in defined regions, where significant responses occurred in at least 50% of the group. Greater than 0.1% increase in BOLD responses were found during at least one of the tactile attention tasks in contralateral parietal opercular OP1, BA 4 finger region, frontal eye field, dorsal premotor, anterior and posterior BA 7, and bilaterally in superior temporal sulcal cortex (BA 22), ventral premotor, supplementary motor area, and frontal operculum/insula. The same tasks suppressed activity in ipsilateral OP4. The BA 22 ROI showed larger responses during neutral cuing. The control task suppressed BOLD in ipsilateral OP1 and OP4 and bilaterally in BA 40, but significantly enhanced responses in dorsal parietal-frontal regions compared with tactile attention tasks. No regional differences were found between selectively cued frequency and duration tasks. Tactile attention effects were most prominent in OP1. Posterior parietal responses possibly reflected the visual attention required for backwards-counting, whereas the frontal regions potentially related to goal-directed behavior when identifying target stimulation.

Figure 1

Task paradigm. Top: Epochs contained three successive trials each of which involved paired vibrations (vertical bars). Vibration duration was a variable that was set between 956 and 1,045 ms (Table I). The interval between pairs was fixed at 500 ms. A ∼3 s interval followed each trial for participant responses. Trial timing was synchronized to the 1st, 3rd, or 5th TR frames (black arrows). However, there were slight differences in the interval between the onset of the TR and the first vibration in order to accommodate a range of differences in vibration durations. Vibrotactile stimulation occurred during volume acquisitions for TR frames 2, 4, and 6, and given hemodynamic delays, also affected images collected during TR frames 3, 5, and 7. Middle: A visual cue was present during vibration stimulation. Bottom: Vertical lines mark the beginning of 10 successive TR frames.

Figure 2

F‐statistic Z‐score maps for a single participant. Volume data and surface maps are shown from the same individual during neutral cuing (N) and selective cuing to frequency (SF) tasks. A: Horizontal slices (Z = 46) taken through regions marked on the surface rendered cortex. Coronal slices taken near the centers of four ROI: PMv, BA 1, Ant. 7, and Post. 7. B: Inflated view of surface was obtained after segmentation and surface rendering of participant's left hemisphere. Arrows point at centers of gravity (COG) for ROI: PMv, BA1, BA7‐anterior, and BA7‐posterior. Corresponding locations are marked by + on the coronal slices in A. COG based on composite conjunction maps for 12 participants (see text). C: The same regions are noted in a flattened model for the left hemisphere of this individual.

Figure 3

Defined regions of interest (ROI) were painted onto a standard surface mesh of nodes (PALS‐B12 atlas). Top Row: Borders (green lines) drawn on inflated hemispheres indicate selected Brodmann areas and probabilistic parietal opercular regions (description and methods for creating inflated and flat maps can be found in Van Essen, 2005). Second Row: ROI painted onto a flattened representation of the PALS‐B12 atlas. Third Row: Enlargment shows the borders of the four parietal opercular regions defined previously (Eickhoff et al., 2006c) and the opercular ROI (black lines) defined within these borders in the current study.

Figure 4

Multiple comparison corrected group‐level significance maps per task. ROI boundaries are shown in black and are identified in Figure 3.

Figure 5

Regional time course graphs by task. Findings from left and right hemisphere ROI are shown, respectively, in the two left and furthest right two columns of graphs. Data at each interval represent the group mean; for clarity only upward standard error bars are shown. Vibration trial timing (see Fig. 1), scaled to the graph ordinates, is shown below each column of graphs.