Dr. Ali Jeewajee

Ali’s research deals with how the environmental novelty is signaled by reduction of the hippocampal theta frequency. The hippocampal formation (HF) plays a key role in novelty detection, but the mechanisms remain unknown. Novelty detection aids the encoding of new information into memory - a process thought to depend on the HF and to be modulated by the theta rhythm of EEG. Ali examined EEG recorded in the HF of rats foraging for food within a novel environment, as it became familiar over the next five days, and in two more novel environments unexpectedly experienced in trials interspersed with familiar trials over further days. Ali found that environmental novelty produces a sharp reduction in the theta frequency of foraging rats, that this reduction is greater for an unexpected environment than for a completely novel one, and that it slowly disappears with increasing familiarity. These results do not reflect changes in running speed and suggest that the septo-hippocampal system signals unexpected environmental change via a reduction in theta frequency. In addition, Ali’s research provides evidence in support of a cholinergically mediated mechanism for novelty detection, has important implications for our understanding of oscillatory coding within memory and for the interpretation of event-related potentials, and provides indirect support for the oscillatory interference model of grid cell firing in medial entorhinal cortex.

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