Subcortical Interactions Between Somatosensory Stimuli of Different Modalities and Their Temporal Profile

Abstract

Costa J, Valls-Solé J, Valldeoriola F, Rumià J. Subcortical interactions between somatosensory stimuli of different modalities and their temporal profile. J Neurophysiol 100: 1610 -1621, 2008. First published July 2, 2008 doi:10.1152/jn.90412.2008. Interactions between inputs of different sensory modality occur along the sensory pathway, including the thalamus. However, the temporal profile of such interaction has not been fully studied. In eight patients who had been implanted an intrathalamic electrode for deep brain stimulation as symptomatic treatment of tremor, we investigated the interactions between mechanical taps and electrical nerve stimuli. Somatosensory evoked potentials (SEPs) were recorded from Erb's point, cervical spinal cord, nucleus ventrointermedialis of the thalamus, and parietal cortex. A handheld electronic reflex hammer was used to deliver a mechanical tap to the skin overlying the first dorsal interosseous muscle and to trigger an ipsilateral digital median nerve electrical stimulus time-locked to the mechanical tap with a variable delay of 0 to 50 ms. There were significant time-dependent interactions between the two sensory volleys at the subcortical level. Thalamic SEPs were decreased in amplitude at interstimulus intervals (ISIs) from 10 to 40 ms with maximum effect at 20 ms (Ϫ42.8 Ϯ 10.5%; P Ͻ 0.001). A similar decrease was also seen in the number and frequency of the high-frequency components of thalamic SEPs (Ϫ25 Ϯ 4%). A smaller reduction (Ϫ18.1 Ϯ 5.8%; P Ͻ 0.001) was present in upper cervical response at ISI ϭ 20 ms. There were no changes in peripheral responses. Cortical SEPs were almost completely absent in some subjects at ISIs from 20 to 50 ms. There were no changes in SEP latencies. Our results indicate that significant time-dependent interactions between sensory volleys occur at the subcortical level. These observations provide further insight into the physiological mechanisms underlying afferent gating between sensory volleys of different modality.

Transient and steady-state responses to mechanical stimulation of different fingers reveal interactions based on lateral inhibition

“…The interaction effects in the thalamus have a recovery time of about 40 ms, which implies that ISIs longer than 40 ms will not evoke interaction effects (Costa et al 2008). These results are compatible with the notion that active lateral inhibitory processes rather than occlusion effects underlie the thalamic interaction effects.…”

“…For normal CNS function it is important that relevant sensory information is selected from multiple concurrent sources. The interaction effects described in this paper most likely have a role in this perceptual filtering (Costa et al 2008) which can serve as protection of preattentive stimulus processing (Graham 1992). Another functional role of interaction between simultaneous stimuli could be facilitation of sensory integration.…”

“…These results are compatible with the notion that active lateral inhibitory processes rather than occlusion effects underlie the thalamic interaction effects. In somatosensory cortex the recovery of early cortical responses, such as the N20 component, however, continues after 50 ms (Costa et al 2008) and can be as large as 120 to 150 ms (Huttunen et al 1992, Wikstrom et al 1996. Quite surprisingly, later components like the P60 are attenuated for ISI's as large as one second (Wikstrom et al 1996).…”

“…Interaction of somatosensory impulses has been found at different levels of the somatosensory pathway, from brainstem to cortex (Costa et al 2008, Hsieh et al 1995. The recovery time of these interaction effects differs between subcortical and cortical responses.…”

“…Furthermore, there are some indications that lateral inhibition is most likely responsible for the interaction effect (Costa et al 2008, Huttunen et al 1992. However, to our knowledge no study was able to clearly disentangle the two mechanisms.…”