The neurogenesis of P1 and N1: A concurrent EEG/LFP study

Abstract

It is generally recognised that event related potentials (ERPs) of electroencephalogram (EEG) primarily reflect summed post-synaptic activity of the local pyramidal neural population(s). However, it is still not understood how the positive and negative deflections (e.g. P1, N1 etc) observed in ERP recordings are related to the underlying excitatory and inhibitory post-synaptic activity. We investigated the neurogenesis of P1 and N1 in ERPs by pharmacologically manipulating inhibitory post-synaptic activity in the somatosensory cortex of rodent, and concurrently recording EEG and local field potentials (LFPs). We found that the P1 wave in the ERP and LFP of the supragranular layers is determined solely by the excitatory post-synaptic activity of the local pyramidal neural population, as is the initial segment of the N1 wave across cortical depth. The later part of the N1 wave was modulated by inhibitory post-synaptic activity, with its peak and the pulse width increasing as inhibition was reduced. These findings suggest that the temporal delay of inhibition with respect to excitation observed in intracellular recordings is also reflected in extracellular field potentials (FPs), resulting in a temporal window during which only excitatory post-synaptic activity and leak channel activity are recorded in the ERP and evoked LFP time series. Based on these findings, we provide clarification on the interpretation of P1 and N1 in terms of the excitatory and inhibitory post-synaptic activities of the local pyramidal neural population(s).

Modeling Neural Adaptation in Auditory Cortex

“…This contrasts with previous reports that these bi-phasic deflections reflect sequences of excitatory (P1) followed by inhibitory (N1) post-synaptic inputs (Tan et al, 2004 ; Oswald et al, 2006 ). However, a similar finding was reported in a recent study of rat somatosensory cortex where reduced inhibitory post-synaptic activity affected only the late phase of the N1 by increasing its peak and duration (Bruyns-Haylett et al, 2017 ). Based on the time course and morphology of the simulated LFP components, we speculate that the initial positivity (P1) reflected bottom-up activity of the basal dendrites of pyramidal neurons in layers II/III as shown in Figure 4 .…”

Concurrent Recording of Co-localized Electroencephalography and Local Field Potential in Rodent

“…Finally, comparison of the temporal dynamics of the ERP and that of the evoked LFP across cortical layers suggest that somatosensory evoked potential reflects better the LFP in the supragranular layer of the cortex than that in the granular and infragranular layers. This is in agreement with our earlier work 6 , demonstrating that the initial segment (P1) of the ERP is related to the return current arising from the inflow of the excitatory synaptic current occurring in the granular layer, while the subsequent decrease (N1) in ERP may be related to the delayed arrival of thalamic afferent to cortical layers II/III and/or feedforward signals from deeper cortical layers. In conclusion, concurrent recordings of EEG/LFP can enhance understanding of the neural genesis of EEG, and facilitate the mathematical modeling of EEG in terms of neural signals across cortical layers.…”

“…It is generally accepted that LFPs recorded via microelectrodes primarily reflect the weighted sum of synchronized excitatory and inhibitory synaptic activities of local pyramidal neural populations 1 2 3 4 . Our recent research demonstrated that the profile of the LFP signal could be separated into components of excitation and inhibition 5 6 . However, as LFP is normally measured via an invasive procedure, it is not suited for most studies of the human brain.…”

Lateral inhibition in the autism spectrum: An SSVEP study of visual cortical lateral interactions

“…The neural response to low-level visual stimuli, measured through the visual evoked potential (VEP), is the net result of excitatory and inhibitory mechanisms governing many low-level visual features. The direct effect of inhibitory processes on the VEP has been demonstrated by applying a GABA A antagonist to visual and somatosensory cortices of animal models (Bruyns-Haylett et al 2017;Daniels and Pettigrew 1975;V Zemon et al 1980). These studies show that specific positive and negative aspects of the VEP time series are increased and decreased in magnitude following topical application of a GABA antagonist to the visual cortex of cats (V Zemon et al 1980;Vance Zemon, Kaplan, et al 1986).…”