# Somatosensory Mismatch Response in Patients with Cerebral Palsy
## 4 Discussion  
Somatosensory evoked event-related potentials were recorded in healthy individuals and patients with cerebral palsy to verify the presence of mismatch-related ERP components especially in patients with CP. The central findings of the study are as follows:  
* The mismatch-related somatosensory responses can be observed in patients with cerebral palsy. * In line with our assumption, the observed mismatch-related ERP components from frontal and parietal channels were statistically significant at two predefined latency ranges: \(F\)2 and \(P\)4 channels at 150-250 ms and \(F\)4 and \(P\)4 channels at 350-450 ms after the stimulus onset. The observed response in the time range of 150-250 ms is considered as sMMN, and the response in the time range of 350-450 ms is considered as LDN. In terms of time window and channel location, these findings are qualitatively in good agreement with the studies involving healthy adults [21; 25]. In an early study on auditory MMN, [PERSON] et al. [42] proposed that MMN rises at around 100-150 ms after stimulus onset and peaks at around 200-250 ms over the front-tocentral areas of the scalp. Later on, further studies confirmed that auditory MMN is generated in the temporal and frontal areas [34]. In most somatosensory studies, MMN has been confirmed over the frontcentral regions as either a negative or positive component at about 100-250 ms of latency [7; 11; 12]. Some other studies found mismatch-related ERP responses at two separate latencies. For example, [PERSON] et al. [6] found sMMN centroparietally at 180-220 ms and frontocentrally at 250-290 ms after the stimulus onset in adults (22-36 years). [PERSON] et al. [12] reported a frontocentral negative peak at 100-200 ms, followed by a centroparietal positive shift at 150-250 ms to vibrotactile presented changes in duration and frequency. On the other hand, [PERSON] et al. [7; 43] found a significantly enhanced sMMN in early negativity (30-70 ms) and later a positive peak at 100-200 ms after stimulus. Similarly, [PERSON] et al. [41] reported an sMMN response over the frontal midline scalp with two phases of MMN waveform: an earlier negative peak at \(\sim\)145 ms, followed by a positive peak at \(\sim\)235 ms. Our present sMMN peak between 150 and 250 ms agrees with the findings of [PERSON] et al. [6], and the appeared peak between 350 and 450 ms is likely representing LDN [25; 44]. Figure 4: (**a**) The left and right panels show the distributions for the statistically significant channels, e.g., \(F\)2 and \(P\)4, along with their box plots for the time window 150–250 ms. The middle panel shows the scalp topographic maps for this time window. STD—standard; DEV—deviant; DIFF—deviant minus standard. (**b**) The same but for the statistically significant channels, e.g., \(F\)2 and \(P\)4, for the time window 350–450 ms. The results indicate the presence and observability of mismatch-related components in the case of patients with CP. Nevertheless, this study has certain limitations that should be explored and addressed in subsequent research. A central limitation is the relatively small and inhomogeneous patient cohort. While this limitation does not affect the main finding of this study, the data provide insufficient power for more in-depth investigations. A larger patient cohort would, for instance, enable the examination of relationships between clinical parameters, such as somatosensory impairments, and the expression of mismatch-related ERP responses, providing an important basis for the establishment of mismatch-related ERP responses as diagnostic or monitoring biomarkers in CP. Another limitation relates to the fixed interstimulus interval (ISI) rather than a randomized ISI, which is typically favored in the design of ERP studies. While a definite confirmation of whether this has an effect on the observed mismatch-related ERP responses requires further research, we expect, if at all, a randomized ISI to lead to a rather larger effect size relative to a fixed ISI due to the habituation effect.