Somatosensory evoked field in response to visuotactile stimulation in 3- to 4-year-old children

Abstract

A child-customized magnetoencephalography system was used to investigate somatosensory evoked field (SEF) in 3- to 4-year-old children. Three stimulus conditions were used in which the children received tactile-only stimulation to their left index finger or visuotactile stimulation. In the two visuotactile conditions, the children received tactile stimulation to their finger while they watched a video of tactile stimulation applied either to someone else's finger (the finger-touch condition) or to someone else's toe (the toe-touch condition). The latencies and source strengths of equivalent current dipoles (ECDs) over contralateral (right) somatosensory cortex were analyzed. In the preschoolers who provided valid ECDs, the stimulus conditions induced an early-latency ECD occurring between 60 and 68 ms mainly with an anterior direction. We further identified a middle-latency ECD between 97 and 104 ms, which predominantly had a posterior direction. Finally, initial evidence was found for a late-latency ECD at about 139-151 ms again more often with an anterior direction. Differences were found in the source strengths of the middle-latency ECDs among the stimulus conditions. For the paired comparisons that could be formed, ECD source strength was more pronounced in the finger-touch condition than in the tactile-only and the toe-touch conditions. Although more research is necessary to expand the data set, this suggests that visual information modulated preschool SEF. The finding that ECD source strength was higher when seen and felt touch occurred to the same body part, as compared to a different body part, might further indicate that connectivity between visual and tactile information is indexed in preschool somatosensory cortical activity, already in a somatotopic way.

Keywords: magnetoencephalography; preschool child; somatosensory cortex; somatosensory evoked field; visuotactile stimulation.

Figure 1

Visuotactile stimulation used during MEG measurements of preschool somatosensory cortex. While tactile stimulation was applied to the left index finger, 3- to 4-year-old children watched tactile stimulation to someone else’s left index finger (finger-touch condition) or to someone else’s toe (toe-touch condition). The tactile stimulation to the children’s left index finger during MEG measurements was applied through a piezo-electric stimulator (A), decorated with a butterfly-like stuffed doll [(B) top-view; (C) top-view with child’s finger; (D) side-view].

Figure 2

Preschool ECD latencies and source strengths in the tactile-only condition. ECDs were obtained during piezo-electric stimulation to the left index finger of 3- to 4-year-old children. Note that the same participant could have provided data for more than one latency category, i.e., showed double-peak or triple-peak deflections in the MEG waveform that obeyed the ECD criteria. LN, natural logarithm; nA-m, nano-Ampere per meter; ms, milliseconds.

Figure 3

Preschool ECD locations and directions in the tactile-only condition. ECDs were obtained during tactile stimulation to the left index finger, resulting in ECD locations in contralateral right hemisphere. Early-latency ECDs predominantly had an anterior direction. No significantly dominant direction pattern was observed for middle-latency and late-latency ECDs. Note that the same participant could have provided data for more than one category, i.e., showed double-peak or triple-peak deflections in the MEG waveform that obeyed the ECD criteria.

Figure 4

Preschool ECD latencies and source strengths in paired tactile-only and finger-touch conditions. Circles show the tactile-only data and squares show the finger-touch data. White symbols show early-latency pairs (n = 6), black symbols show middle-latency pairs (n = 8), and gray symbols show late-latency pairs (n = 4). In the middle-latency category, ECD source strength was significantly higher in the finger-touch (filled black squares) than in the tactile-only condition (filled black circles). LN, natural logarithm; nA-m, nano-Ampere per meter; ms, millisecond.

Figure 5

Preschool ECD latencies and source strengths in paired tactile-only and toe-touch conditions. Circles show the tactile-only data and triangles show the toe-touch data. White symbols show early-latency pairs (n = 13), black symbols show middle-latency pairs (n = 7), and gray symbols show late-latency pairs (n = 5). In the middle-latency category, ECD source strength was higher in the tactile-only (filled black circles) than in the toe-touch condition (filled black triangles), but the difference strictly did not reach significance with Bonferroni correction of the alpha-level. LN, natural logarithm; nA-m, nano-Ampere per meter; ms, millisecond.

Figure 6

Preschool ECD latencies and source strengths in paired finger-touch and toe-touch conditions. Squares show the finger-touch data and triangles show the toe-touch data. White symbols show early-latency pairs (n = 11), black symbols show middle-latency pairs (n = 7), and gray symbols show late-latency pairs (n = 7). In the middle-latency category, ECD source strength was significantly higher in the finger-touch (filled black squares) than in the toe-touch condition (filled black triangles). LN, natural logarithm; nA-m, nano-Ampere per meter; ms, millisecond.

Figure 7

An example of preschool SEF waveforms in the visuotactile finger-touch condition (left) and the toe-touch condition (right). The waveforms (top) and estimated ECDs (bottom) are shown for a 36-month-old girl. fT, femto-Tesla.

Figure 8

Preschool ECD locations and directions in paired finger-touch and toe-touch conditions. ECDs were obtained during tactile stimulation to the left index finger, while the children watched a video of tactile stimulation to someone else’s finger (finger-touch) or toe (toe-touch). Note that the same participant could have provided data for more than one category, i.e., showed double-peak or triple-peak deflections in the MEG waveform that obeyed the ECD criteria.