Beat Detection Recruits the Visual Cortex in Early Blind Subjects

Abstract

Using functional magnetic resonance imaging, here we monitored the brain activity in 12 early blind subjects and 12 blindfolded control subjects, matched for age, gender and musical experience, during a beat detection task. Subjects were required to discriminate regular ("beat") from irregular ("no beat") rhythmic sequences composed of sounds or vibrotactile stimulations. In both sensory modalities, the brain activity differences between the two groups involved heteromodal brain regions including parietal and frontal cortical areas and occipital brain areas, that were recruited in the early blind group only. Accordingly, early blindness induced brain plasticity changes in the cerebral pathways involved in rhythm perception, with a participation of the visually deprived occipital brain areas whatever the sensory modality for input. We conclude that the visually deprived cortex switches its input modality from vision to audition and vibrotactile sense to perform this temporal processing task, supporting the concept of a metamodal, multisensory organization of this cortex.

Keywords: beat perception; early blindness; multisensory integration; rhythm perception; touch; vision.

Figure 1

Brain activation maps specific to beat detection. Regions activated in each modality in the contrast (“beat” minus “no beat”) are displayed according to the color scale that codes for the activation level based on the t-values. A: Middle frontal gyrus (BA 9); B: inferior frontal gyrus (BA 44/6); C: precentral gyrus/middle frontal gyrus (BA 6); D: superior temporal gyrus (BA 22); E: medial frontal gyrus (BA 6); F - G: putamen; R: right; L: left.

Figure 2

Differences in brain activation during beat processing as a function of the group. Regions activated in each modality in the contrast (early blind (EB) minus sighted controls (SC)) are displayed according to the color scale that codes for the activation level based on the t-values. A: Inferior frontal gyrus (BA 46); B: insula (BA 13); C: inferior temporal gyrus/fusiform gyrus (BA 37); D: precuneus (BA 7); E - F - G: cuneus (BA 18); R: right; L: left.

Figure 3

Differences in brain activation specific to beat detection as a function of the group. Brain areas with a higher activity level in blind participants compared to controls and specific to beat detection in each modality (group by condition interaction maps in GLM) are displayed according to the color scale that codes for the activation level based on the t-values. A - B - C: Lingual gyrus (BA 18); D: inferior occipital gyrus (BA 19); E: middle frontal gyrus (BA 46); F: inferior frontal gyrus (BA 44); G: insula (BA 13); H: middle temporal gyrus/middle occipital gyrus (BA 37/19); I: insula (BA 13); R: right; L: left.

Figure 4

Relationship between beat detection performance and brain activity. The activation maps were obtained using an analysis of covariance between the brain activity for the contrast (“beat” minus “no beat”) and the individual response time for beat detection in the corresponding modality used as the covariate (p < 0.005). The color scale codes for the activation level based on the r coefficient. A: Inferior frontal gyrus (BA 46); B: middle frontal gyrus (BA 46); C: inferior frontal gyrus (BA 9); D: insula (BA 13); E: inferior parietal lobule (BA 40); F: fusiform gyrus (BA 37); G: inferior temporal gyrus/middle occipital gyrus (BA 37/19); H: inferior occipital gyrus (BA 19); I: precentral gyrus/middle frontal gyrus (BA 6); J: inferior frontal gyrus (BA 45/46); K: middle occipital gyrus (BA 19); L: inferior frontal gyrus (BA 45/46); M: middle frontal gyrus (BA 9); N: middle frontal gyrus/precentral gyrus (BA 6); O: inferior parietal lobule (BA 40); P: insula (BA 13); Q: putamen. R: right; L: left.