page_title: Sharp waves and ripples
section_title: Effects of neocortical inputs
hierarchical_section_title: Sharp waves and ripples / Hippocampal formation / Network mechanisms of generation / Effects of neocortical inputs
context_page_description: Sharp waves and ripples are oscillatory patterns in the mammalian brain hippocampus seen on an EEG during immobility and sleep. There are three major network oscillation patterns in the hippocampus: theta waves, SWRs and gamma waves. Gamma oscillations are found in all major brain structures, whereas theta and sharp waves are specific to the hippocampus and its neighbouring areas. SWRs are composed of large amplitude sharp waves in local field potential and associated fast field oscillations known as ripples. SWRs are shown to be involved in memory consolidation and the replay of wakefulness-acquired memory. These network oscillations are the most synchronous patterns in the brain, making them susceptible to pathological patterns such as epilepsy.
context_section_description: In spite of the self-emergent nature of the SWRs, their activity could be altered by inputs from the neocortex via the trisynaptic loop to the hippocampus. Activity of the neocortex during slow wave sleep is deterministic of inputs to the hippocampus; thalamocortical sleep spindles and delta waves are the sleep patterns of the neocortex. These inputs contribute to the selection of different neuronal assemblies for initiation of SWRs, and affect the timing of the SWRs. Different thalamocortical neuronal assemblies give rise to sleep spindles, and these cell assemblies affect the burst initiator for the sharp waves. In this manner, thalamocortical inputs affect the content of the SWRs going to neocortex.
caption: sleep spindle and K-complex in EEG