In recent years, fNIRS studies of epilepsy have provided promising results, which in time may lead to clinical usefulness. However, much more work is necessary as fNIRS still has several limitations that prevents it from being a mature technique in clinical settings. To begin with, one problem concerns the interpretation of fNIRS results, as the relation between the measured hemodynamic change and the underlying neural activity is not fully understood. For example, evidence of a deoxygenation process can be detected during some seizures both in our study and in previous work.18,19,22,24 Whether the factors such as the type of seizures, their duration, their frequency, age, or other comorbid conditions are underlying the deoxygenation remains to be investigated. On the other hand, the HRF shape for IEDs was also reported to vary across patients and brain regions in previous BOLD-fMRI studies.72,73 Our recent work tried to estimate the HRF while accounting for the patient-specific variability and nonlinearity to some extent,47 but did not provide a standard solution for the analysis of IEDs with fNIRS. The other critical issue is the SNR of fNIRS signals. fNIRS data acquisition can be disturbed by movement artifacts especially during seizures. While several methods have been proposed to address this problem either with additional equipment22,74 or with signal denoising techniques,33,75,76 there is still no standard method for the correction of motion artifacts in fNIRS signals.77 Another factor that might lower the SNR of fNIRS signals is the unknown contribution from extracerebral tissue, as the averaged path of photon propagation is considered to follow a banana-shaped pattern from superficial layers (e.g., skin, scalp, skull, etc.) to cerebral cortex. The extracerebral contamination would further interfere with data interpretation by reducing fNIRS sensitivity to brain tissue, which gets worse if channels with shorter-than-typical separation (e.g., ) are employed in the SD layout.78,79 Recent studies concluded that signals recorded from very short SD separations (80) may be used to filter out the some of the physiological noise arising from superficial tissues.81–83 However, installing short channels together with long channels will probably lead to reduced head coverage, which is disadvantageous in epilepsy studies aimed at the localization of the focus region. Finally, it must be reminded that fNIRS can only reliably sample the superficial neocortex due to its limited penetration depth,6,19 a disadvantage shared by surface EEG.