Infragranular sources of sustained local field potential responses in macaque primary visual cortex.

A local field potential (LFP) response can be measured throughout the visual cortex in response to the abrupt appearance of a visual stimulus. Averaging LFP responses to many stimulus presentations isolates transient, phase-locked components of the response that are consistent from trial to trial. However, stimulus responses are also composed of sustained components, which differ in their phase from trial to trial and therefore must be evaluated using other methods, such as computing the power of the response of each trial before averaging.

The Visual Evoked Potential is independent of surface alpha rhythm phase.

A Visual Evoked Potential (VEP) is an electrical signal picked up by a surface electrode in response to the activation of visual cortex by a visual stimulus. Because the VEP is typically much smaller in magnitude than the ongoing spontaneous EEG signal, the VEP is derived by averaging a large number of responses time-locked to stimulus presentation. Standard theory has it that the VEP is independent of the ongoing EEG, however, there has long been a competing view that the VEP is caused by a partial phase reset of the spontaneous alpha rhythm.