Synaptic circuit mechanisms of rhythmic slow oscillatory dynamics in the rodent and human cerebral cortex

Co-ordinated neuronal activity in the brain is intrinsically linked with behaviour. Malfunction of neuronal coordination results in psychiatric and neurological disorders. Much of the brain activity is rhythmic, as rhythmicity facilitates local and global interactions and enables the representation of temporal sequences. Rhythmicity resets the parameters of neuronal population activity for encoding and delivering information in support of behavioural needs. Importantly, the action of single nerve cells as well as groups of neurons can change systematically relative to the population rhythm and is used by the brain for coding of information. We explore a widespread rhythmicity in the cerebral cortex in the so-called theta frequency range (4-12 cycles per second) in rodents and the homologous brain areas in humans. Theta oscillations are linked to higher frequency oscillations associated with cognitive processes. Such linking of rhythmicity with different frequencies is a basic principle of the brain, as changes in the strength of links indicate behavioural performance, cognitive states such as navigation, decision-making and memory and are impaired by pathology such as dementia. We identify the nerve cells, the links between them, and sites where influencing the memory system with drugs, or changing the activity of selected pathways restores normal rhythmic activity and improves co-ordination by attenuating pathological activity.