Confronted with the loss of one type of sensory input, we compensate using information conveyed by other senses. However, losing one type of sensory information at specific developmental times may lead to deficits across all sensory modalities. We addressed the effect of auditory deprivation on the development of tactile abilities, taking into account changes occurring at the behavioral and cortical level. Congenitally deaf and hearing individuals performed two tactile tasks, the first requiring the discrimination of the temporal duration of touches and the second requiring the discrimination of their spatial length. Compared with hearing individuals, deaf individuals were impaired only in tactile temporal processing. To explore the neural substrate of this difference, we ran a TMS experiment. In deaf individuals, the auditory association cortex was involved in temporal and spatial tactile processing, with the same chronometry as the primary somatosensory cortex. In hearing participants, the involvement of auditory association cortex occurred at a later stage and selectively for temporal discrimination. The different chronometry in the recruitment of the auditory cortex in deaf individuals correlated with the tactile temporal impairment. Thus, early hearing experience seems to be crucial to develop an efficient temporal processing across modalities, suggesting that plasticity does not necessarily result in behavioral compensation.

Perception of the outside world results from integration of information simultaneously derived via multiple senses. Increasing evidence suggests that the neural underpinnings of multisensory integration extend into the early stages of sensory processing. In the present study, we investigated whether the superior temporal gyrus (STG), an auditory modality-specific area, is critical for processing tactile events. Transcranial magnetic stimulation (TMS) was applied over the left STG and the left primary somatosensory cortex (SI) at different time intervals (60, 120, and 180 msec) during a tactile temporal discrimination task (Experiment 1) and a tactile spatial discrimination task (Experiment 2). Tactile temporal processing was disrupted when TMS was applied to SI at 60 msec after tactile presentation, confirming the modality specificity of this region. Crucially, TMS over STG also affected tactile temporal processing but at 180 msec delay. In both cases, the impairment was limited to the contralateral touches and was due to reduced perceptual sensitivity. In contrary, tactile spatial processing was impaired only by TMS over SI at 60–120 msec. These findings demonstrate the causal involvement of auditory areas in processing the duration of somatosensory events, suggesting that STG might play a supramodal role in temporal perception. Furthermore, the involvement of auditory cortex in somatosensory processing supports the view that multisensory integration occurs at an early stage of cortical processing.

It has been suggested that figurative language, which includes idioms, is controlled by the right hemisphere. We tested the right hemisphere hypothesis by using repetitive transcranial magnetic stimulation (rTMS) to transiently disrupt the function of the frontal and temporal areas of the right versus left hemisphere in a group of normal participants involved in a task of opaque idiom versus literal sentence comprehension. Forty opaque, nonambiguous idioms were selected. Fifteen young healthy participants underwent rTMS in two sessions. The experiment was run in five blocks, corresponding to the four stimulated scalp positions (left frontal and temporal and right frontal and temporal) and a baseline. Each block consisted of 16 trials—8 trials with idioms and 8 trials with literal sentences. In each trial, the subject was presented with a written sentence, which appeared on the screen for 2000 msec, followed by a pair of pictures for 2500 msec, one of which corresponded to the sentence. The alternative corresponded to the literal meaning for idioms and to a sentence differing in a detail in the case of literal sentences. The subject had to press a button corresponding to the picture matching the string. Reaction times increased following left temporal rTMS, whereas they were unaffected by right hemisphere rTMS, with no difference between idiomatic and literal sentences. Left temporal rTMS also reduced accuracy without differences between the two types of sentences. These data suggest that opaque idiom and literal sentence comprehension depends on the left temporal cortex.