Table 2.

Different types of physiologic HFOs.

Type	Localization	Relevant findings
Memory-related HFOs	Hippocampus, parahippocampus, entorhinal cortex	Spontaneously and bilaterally occurring (17, 31, 68, 78); coupled with neocortical sleep spindles (93–95); occurrence rate correlates with memory performance (96–98)
Motor-related HFOs	Motor cortex, subthalamic regions	Occur over motor areas (77, 99); highly localized and movement specific (100); associated to symptoms in Parkinson's disease and tremors (101–104)
Somatosensory HFOs	Somatosensory cortex, thalamic regions	Overly the P20 and N20 components of SEPs (105–107); HFOs overlying the ascending N20 phase, possibly reflect presynaptic action potentials and are linked to arousal and critical stimuli detection (108–110); HFOs overlying the descending N20 phase may reflect bursts of inhibitory interneurons (111, 112)
Visually evoked HFOs	Occipital lobe, visual cortex	Spontaneously occurring (90, 92); possibly related to processing of visual stimuli (113–115); evokable by visual stimuli (116)

SEPs, somatosensory evoked potentials.