Indexed on: 09 Apr '20Published on: 09 Apr '20Published in: Brain connectivity
Among various hippocampal rhythms including, sharp wave-ripples, gamma, and theta, theta rhythm is crucial for cognitive processing, particularly learning and memory. Theta oscillations are observable in both humans and rodents during spatial navigations. However, the Hippocampus (Hip) is well known as the generator of current rhythm, other brain areas, like Prefrontal Cortex (PFC), can be affected by theta rhythm, too. The PFC is a core structure for the execution of diverse higher cortical functions defined as cognition. This region is connected to the Hippocampus through the hippocampal-prefrontal pathway; hereby, theta oscillations convey hippocampal inputs to the PFC and simultaneously synchronize the activity of these two regions during memory, learning and other cognitive tasks. Importantly, thalamic Nucleus Reunions (nRE) and Baso-Lateral Amygdala (BLA) are salient relay structures modulating the synchronization, firing rate, and phase-locking of the hippocampal-prefrontal oscillations. Herein, we summarized experimental studies chiefly animal researches in which theta rhythm of the Hip-PFC axis was investigated using either electrophysiological assessments in rodent or integrated diffusion-weighted imaging and electroencephalography (EEG) in human cases under memory-based tasks. Moreover, we briefly reviewed alterations of theta rhythm in some CNS diseases with the main feature of cognitive disturbance. Interestingly, animal studies implied the interruption of theta synchronization in psychiatric disorders such as schizophrenia and depression. In order to disclose the precise role of theta rhythm fluctuations through the Hip-PFC axis in cognitive performances, further studies are needed.