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The P3 can arguably be named the most intensely studied ERP. In spite of more than 40 years of research, fundamental questions regarding the nature of its neural generators remain unresolved. While most studies conclude that the P3 is a true classical "endogenous" potential, and that its surface potential distribution remains constant across sensory modalities, these results are largely based on low-density EEG recordings, without the use of high-resolution methods such as the spherical spline Laplacian (SSL). Seventeen healthy participants performed a three-stimulus oddball task in visual and auditory modality while their EEG was recorded using a 128-channel system. Comparison of amplitude-normalized SSL estimated P3 brain-surface potentials, and analysis of spatial and temporal correlations revealed significant differences between visual and auditory evoked P3 topographies from target and distractor stimuli (but not target minus frequent or distractor minus frequent comparisons). Based on these results, we postulate the likely existence of at least some sensory modality-specific neuronal generators of the P3.

Our aim was to investigate changes in movement-related cortical potentials (MRCPs) in ALS patients with different degrees of upper motor neuron (UMN) involvement. Since respiratory failure is the main cause of death in ALS, changes in inspiratory-related (sniffing) potentials were studied in addition to finger-flexion-related potentials. Subjects (21 ALS, 19 controls) performed two self-paced motor tasks while their EEGs were recorded. The first task required flexions of the right index finger and the second, brisk nasal inspirations. The early (BP1), late (BP2) and motor potential (MP) components of MRCPs were evaluated. Results showed that patients generated higher MRCPs than controls. However, this effect was most significant in the subgroup of patients with low UMN burden (LUB). The high UMN burden (HUB) subgroup did not differ from controls, but had significantly lower MP amplitudes than the LUB subgroup. Progressive UMN deterioration was associated with an initial increase, followed by a later decrease, in MP amplitudes in ALS. In conclusion, the increased MRCPs in LUB compared to HUB patients indicate different processes of ALS pathophysiology that force opposing changes in MRCP amplitudes.

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