Brain health indications from the experience of deja vu (or its absence)

In the intricate labyrinth of the human mind, one phenomenon that has long puzzled scientists is the enigmatic sensation known as deja vu. This feeling of familiarity that accompanies the metacognitive recognition that these feelings are misplaced has been the subject of much research, and new insights are continually emerging.

Akira O'Connor, a Senior Lecturer at the School of Psychology and Neuroscience, University of St Andrews, is one of the researchers leading the charge in understanding how we make decisions about our memories and experience memory.

Several theories have been proposed to explain the brain mechanisms behind deja vu. One of the most prominent is the dual processing theory, which suggests that deja vu arises from a brief delay or misalignment in processing information between the two hemispheres of the brain, causing a false sense of familiarity when the momentary "lag" makes new information feel like a repeated experience.

Another theory is the memory processing theory, which proposes that deja vu happens when the brain struggles to distinguish current experiences from past memories, leading to a sensation that the present is familiar or already experienced. This aligns with neuropsychological views that the brain's memory and recognition circuits momentarily misfire, causing this memory illusion.

The hologram theory suggests that deja vu might result from the brain creating a hologram-like reconstruction of memory fragments, which projects a realistic sense of familiarity for the current experience, though it isn't an exact memory.

Research implicates the temporal lobe (including the hippocampus and fusiform gyrus) in memory reconstruction and perception. Disruptions in the interplay between internally-oriented memory retrieval and externally-oriented perception can produce deja vu. The fusiform gyrus, for example, shows a gradient of sensitivity linking semantic and visual memory features, supporting the integration of perception and memory that might underlie deja vu.

Neuroscientists also highlight the role of frontal brain regions that "fact-check" signals from temporal areas to determine if an experience is genuinely familiar or a false alarm. This process produces the feeling of deja vu when a mismatch is detected but not fully resolved.

While deja vu is not a sign of an unhealthy brain, persistent deja vu, a condition known as 'deja vecu', can make nothing feel new to the affected individuals. This condition is often observed in dementia patients and can be a sign of a worsening condition.

Deja vu is also linked to dopamine, a known mood-booster. Its excitatory effect on the brain regions that signal familiarity may be responsible for some instances of deja vu. Dopaminergic drugs, recreational or otherwise, tend to often cause elevated reports of deja vu.

Factors such as tiredness, stress, dopamine levels, and aging can raise the chance of experiencing deja vu. As people age, they become less able to notice errors, which may lead to fewer instances of deja vu.

Unlike standard forgetting, jamais vu is a disorientating feeling that you don't recognize something when you know you should. In a University of Leeds study, over 70% of participants doubted the correctness of a familiar word after repeating it multiple times, demonstrating the phenomenon of jamais vu. Awareness is crucial in experiencing jamais vu; if you don't notice it, you're not experiencing jamais vu.

In conclusion, deja vu is a complex interplay of memory systems, perception, and neural communication between brain regions, particularly involving temporal lobe structures and frontal cortex monitoring mechanisms. While much is still unknown about this fascinating phenomenon, ongoing research promises to shed more light on the mysteries of the human mind.