The Origin of Sensory Representation: What we can learn from congenital limb deficiencies
Description
We aimed to understand ontology on the organization of the somatosensory representation. Therefore we compared the arrangement of the homunculus in individuals with congenital limb deficiencies (CLD) who have no face and hand co-activation and control subjects. Three of the participants with congenital limb deficiencies (S2, S3, S4) and 15 healthy controls participated in a QEEG experiment. S2 and S3 had bilateral amelia while S4 had tetramelia. We analysed the spectral powers in the electrodes during tactile stimulation of three regions (cheek, shoulder, and foot) and two sides (right and left) to test our specific hypothesis. It is assumed that electrodes C3 and C4 represent the hand area and Cz represents the foot area in healthy controls. In the QEEG analysis, one sample t-tests were performed to compare the spectral powers of the control group and the cases in each electrode. P value was considered significant at 0.05. We measured the alpha activity during left side stimulation of the face, shoulder, and foot, since the C4 electrode is located over the right hemisphere. Since the C3 electrode is located above the left hemisphere, the alpha activity during right-side stimulation of the face, shoulder, and foot was measured. Since the Cz electrode is located centrally, the alpha activity during stimulation of both the left and right face, shoulder, and foot was measured. In general, the alpha activity in the cases was lower than that of the controls in all tactile conditions according to QEEG results. This might be due to being exposed to less tactile stimulation during both prenatal and postnatal periods of their life.
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Steps to reproduce
The experiments were conducted in a quiet room. The participants were seated on an adjustable chair. They were instructed to look at a black screen and not to move during the experiment. The experimenter touched different body regions of the participants in a pre-planned fashion (three facial regions: near the eye, cheek, and lips; two shoulder regions: front and back; back of the neck; and five toes, from the first toe to the little toe. Since S4 has no feet, only the distal regions of the left and right legs were touched). For each region, the examiner touched the body regions on the left side first and then the right side. Each region was stimulated for 3 seconds, and the inter-trial interval was 3 seconds. The experimenter used a finger mouse during tactile stimulus to send the touching signals to the EEG computer. Electrophysiological responses of the participants were recorded using a 32-channel Brain Vision Active electrode QEEG system. The EEG signal was amplified (Brainamp EEG/EP Amplifier, Brain Products, Munich, Germany) and digitised at a 1000 Hz sampling rate (Brainvision Recorder, Brain Products, Munich, Germany). E-Prime 3 software was used to send the triggers to the EEG computer. Electrodes were referenced to Cz during EEG recording, and impedances were kept below 40 kΩ. QEEG Pre-processing QEEG analysis was conducted with BrainVision Analyzer software (BrainProducts GmbH, Munich). The EEG signals were down sampled to 250 Hz and band-pass filtered (0.1–80 Hz). In addition, a 50 Hz notch filter was employed to prevent noise from electrical sources. The data was segmented between -100 and 500 ms, according to the tactile stimulation onset, and baseline corrected. Ocular correction was also applied. If any artifact in that trial remained, the data were excluded. The data were subsequently re-segmented based on the tactile stimulus onset (0–500 ms). Frequency analysis was performed using a fast Fourier transform (FFT) algorithm with Hanning window. Since tactile stimulation has been reported to be associated with alpha suppression in somatosensory areas, spectral power for alpha waves (8–13 Hz) was extracted from the central electrode sites (C3, C4, Cz).
Institutions
- Akdeniz Universitesi