The great British neurologist John Hughlings-Jackson famously described the ‘dreamy state’ reported by some epileptic patients during seizures where they experienced complex hallucinations – sometimes of scenes and faces, feelings of false familiarity and a feeling of ‘weirdness’ or ‘strangeness’.
A study published last year in neurology journal Brain re-examined these experiences by deliberately triggering them by electrically stimulating the brain.
The participants were all patients with epilepsy who were having neurosurgery to treat their otherwise untreatable seizures and the researchers, led by neurologist Jean-Pierre Vignal, specifically stimulated areas in the mesial [inner] temporal lobes.
The feelings of false familiarity are what we normally called d√©j√† vu, but actually we tend to misapply this term as it means ‘already seen’ and refers specifically to a false familiarity for visual perception.
However, it can also occur for anything we experience, such as hearing other people say things, and is more correctly called d√©j√† v√©cu (‘already experienced’) in the literature.
Here are a few of the triggered experiences:
D√©j√† v√©cu (3 volts, right amygdala) – “It’s like yesterday evening … I have the impression that everything around me has been here before, that it has already happened, I feel as if I am going backwards in time”
Scene: reliving a parachute jump (3.5 volts, right hippocampus)
Familiar television advertisement (4 volts, right amygdala)
Impression of being elsewhere (3 volts, right hippocampus)
Scene from childhood (2 milliamps, right amygdala) – “Vision of a bald man dressed in black, coming towards her from behind; associated with a feeling of imminent death; she is pale, with piloerection. She is re-experiencing an experience of anaesthesia by facemask during a tonsillectomy at the age of 14 years”
Impression of being someone else (2 milliamps, left amygdala)
Impression of leaving his body (2.5 milliamps, left amygdala)
Night-time scene (1.2 milliamps, left hippocampus) – “I’m starting to see lots of things, loads of people … it’s still vague and strange. I’ve got an initial picture, a memory … I feel locked in again, something to do with the evening, the night … it’s strange … . like after a party, sad things … there is a mixture of last night and this morning … ‚Äô These remarks were peri-ictal [during the seizure]. After the end of the discharge, there was complete amnesia.”
Scene (4 milliamps, right hippocampus) – “It’s starting, it’s rising up to my eyes … I’m always frightened of something … I feel something, like in dreams, I always see people, loads of people, people that I see in the hospital…”
Familiar character from a film (1.5 millamps, left amygdala)
Ill-defined, unpleasant vision (1.5 milliamps, left hippocampus)
Familiar vision that he is unable to describe (1.5 milliamps, left parahippocampal gyrus)
Vision of a familiar person (1.5 milliamps, left parahippocampal gyrus)
Recent scene (1.5 milliamps, right hippocampus) – “I see myself playing the drums, with people from my family listening to me”
The technique of electrically stimulating the brain to trigger certain experiences was pioneered by Canadian neurosurgeon Wilder Penfield and there’s an excellent account of his life and work on Neurophilosophy if you’d like some background.
This new study is open-access and completely fascinating, so is definitely worth a read.
Link to ‘The dreamy state: hallucinations of autobiographic memory evoked by temporal lobe stimulations and seizures’.
Mind Hacks 
My background is in electrical engineering, so I am curious – do you know how the variable voltage and variable current electrodes each affect the brain differently? Or perhaps how they arrived at the pulse shapes and duration most useful for experiments?