In the murky interior of the brain's left and right temporal lobes can be
found the entorhinal cortex. This structure is located not far from the
hippocampus and is known to be vital for memory processing.
As the Alzheimer's disease process gets under way in the brain, the
entorhinal cortex may be the first brain structure to deteriorate
(Psychiatric News, September 1, 2000). Also, small left and right
entorhinal cortices have been associated with the delusions of schizophrenia
(Psychiatric News, October 1). And now, the entorhinal cortex has
been linked with dèjá vu phenomena—that is, the feeling of
having already experienced the same place or event before.
The finding comes from Fabrice Bartolomei, M.D., Ph.D., an associate
professor at the Service de Neurophysiologie Clinique in Marseille, France.
Results appeared in the September Neurology.
Dèjá vu experiences are a common feature of temporal lobe
seizures and have often been reported after stimulating healthy subjects'
medial temporal lobes. Such evidence suggests that the middle area of the
temporal lobes gives rise to such experiences. But where in the middle region
of the temporal lobes might dèjá vu phenomena arise? Some
research has suggested that it might be in the hippocampus and amygdala since
electrical stimulation of these structures has, on occasion, provoked
dèjá vu experiences in subjects. However, the possibility that
dèjá vu experiences might arise from two other structures
located near each other in the middle area of the temporal lobes—the
entorhinal cortex and the perirhinal cortex—has not been explored. So
Bartolomei and his colleagues decided to do so.
From 2000 to 2002, some 100 patients with drug-resistant epilepsy had a
comprehensive evaluation at the clinic where Bartolomei and colleagues worked.
This included the placement of electrodes in various areas of their temporal
lobes to determine where their seizures were triggered and also to map areas
in their temporal lobes involved in memory or language. The brain areas
stimulated included not just the hippocampus and amygdala, but the entorhinal
cortex and the perirhinal cortex.
Bartolomei and his team then focused on 24 of these patients or, more
specifically, on the 280 electrode stimulations that these subjects had
received to the hippocampus, amygdala, entorhinal cortex, and perirhinal
Dèjá vu states, they found, were mostly associated with the
entorhinal cortex. They occurred with 14 stimulations of the entorhinal
cortex. In contrast, only two stimulations of the perirhinal cortex, two
stimulations of the amygdala, and one stimulation of the hippocampus led to
The investigators were also interested in locating the brain source of
reminiscences. One subject, for instance, upon stimulation of the amygdala,
thought that she smelled the scent of burnt wood. This olfactory hallucination
reminded her of sitting around a campfire on a beach in Brittany when she was
14 years old.
However, it was only this one-time stimulation of the amygdala in one
subject that produced such reminiscences, the researchers found. Stimulations
of the hippocampus or entorhinal cortex provoked no such reminiscences. Yet,
in contrast, five stimulations of the perirhinal cortex led to such
"Our study shows that an illusion of familiarity is often obtained
after stimulation of the rinal cortices (entorhinal cortices or perirhinal
cortices) and more rarely after hippocampal or amygdala stimulation,"
the scientists observed in their study report. How stimulation of the
entorhinal cortex or perirhinal cortex actually produces such illusions is
still a mystery, though, they stated.
"Since this study was conducted on treatment-refractory epileptic
patients, the findings may not be generalizable to healthy subjects,"
Konasale Prasad, M.D., a research fellow at the University of Pittsburgh and
one of the investigators who linked entorhinal cortex abnormalities with
schizophrenia delusions, said in an interview. "Besides, we are not sure
whether the raters who documented and interpreted the findings were blind. A
control subject group or within-group control subjects with sham stimulations
could have also been used to make the findings more
This image of the human brain shows the location of the entorhinal
Photo: Konasale Prasad, M.D., et al.
Nonetheless, Prasad continued, "the findings are not only very
interesting, but very strong and significant for the field of cognitive
neuroscience.... This is the best direct evidence of entorhinal involvement in
dèjá vu states."
"The Bartolomei finding in a way explains our entorhinal cortex
findings in schizophrenia," Matcheri Keshavan, M.D., a professor of
psychiatry at the University of Pittsburgh and another of the scientists who
linked entorhinal cortex abnormalities with schizophrenia delusions, told
"Perhaps an increased activation of the entorhinal cortex in some
schizophrenia patients makes them attach a false sense of familiarity to
otherwise neutral events, leading to delusion formation. Thus, in a classic
example of a delusion, the patient sees a silver spoon on the table. Rather
than dismissing it as an ordinary spoon of no relevance, his entorhinal cortex
may attach a dèjá vu—like feeling. The corrupted retrieval
of the autobiographic memory system, perhaps involving the parahippocampal
gyrus, weaves a delusion around that feeling—`This must mean that I have
The study was funded by the Institut National de la Santè et la
Recherche Scientifique and the University of the Mediterranean.
An abstract of the report, "Cortical Stimulation Study of the
Role of Rhinal Cortex in Dèjá Vu and Reminiscence of
Memories," is posted online at<www.neurology.org/cgi/content/abstract/63/5/858>.▪