People with epilepsy sometimes recall old dreams during seizures. Now a study has found that stimulating a particular part of their brains with electricity can also make this happen.
鈥淚 saw something, a dream 鈥� a nightmare I had a couple of years ago. An object on a table,鈥� said one person analysed in the study.
This phenomenon is called d茅j脿-r锚v茅, which means 鈥渁lready dreamed鈥�. While 诲茅箩脿-惫耻 is a feeling of familiarity for a new situation, d茅j脿-r锚v茅 seems to be much rarer, and usually involves recalling a thought experience that happened while sleeping.
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To understand it better, Jonathan Curot, of Toulouse University Hospital, France, and his colleagues collected examples of d茅j脿-r锚v茅 from 23 people from published studies, and seven people whose experiences had been recorded in epilepsy treatment databases.
All of them reported d茅j脿-r锚v茅-like occurrences when undergoing electrical brain stimulation to assess which regions of their brains seemed to be involved in their epileptic seizures.
Brain stimulation
鈥淚 had the reminiscence of a dream I had a few days ago,鈥� said another. 鈥淚 was in a closed room, I felt the atmosphere, [and] I saw an orange colour,鈥� said one person who received brain stimulation at the epilepsy treatment centre where Curot works.
Altogether, they found evidence for 42 instances of d茅j脿-r锚v茅, which fell into three different categories. Some people reported feeling like dreaming during brain stimulation, whereas others said they found themselves reminiscing about things they thought they had seen before in a dream. The third type involved recalling a specific dream that a person said they had had before.
Analysing these cases revealed that stimulation of a particular part of the brain 鈥� the temporal lobe 鈥� can provoke d茅j脿-r锚v茅. This is involved in long-term memory, dreaming, and forming memories during sleep.
Dream discovery
The team found no evidence that 诲茅箩脿-惫耻 can be stimulated by zapping the same sites that cause d茅j脿-r锚v茅, which suggests these are two distinct phenomena caused by different parts of the brain. Stimulation of d茅j脿-r锚v茅 associated-regions did, however, also produce more general reminiscences of other, non-dream memories.
D茅j脿-r锚v茅 is rare in people with epilepsy, and Curot says there is no evidence yet that it occurs in people who don鈥檛 have the condition 鈥� although it might.
鈥淓lectrical brain stimulation makes it possible to trap this phenomenon that is almost impossible to trap in everyday life,鈥� says Curot. His team suggests the technique may be of use to researchers looking for new methods to investigate dreams. However, such researchers would likely need to find a less invasive stimulation technique that doesn鈥檛 involve inserting electrodes in the brain.
Brain Stimulation
Read more: We dream loads more than we thought 鈥� and forget most of it
