The brain's bastion of memory—the hippocampus—is known to be
small not only in persons with major depression, posttraumatic stress
disorder, and Alzheimer's disease, but also in individuals with
Yet how might a diminutive hippocampus relate to memory problems in
Perhaps by making it difficult for schizophrenia patients to recognize
novel items, a new study suggests. The study was headed by Anthony Weiss,
M.D., a psychiatrist specializing in brain imaging at Massachusetts General
Hospital in Boston. Results are in press with Biological
During the past few years, investigators have reported that persons with
schizophrenia have small hippocampal volumes and that they have certain memory
difficulties. Weiss and his team assessed whether a small hippocampus might be
associated with memory problems in schizophrenia.
Their subjects were 15 chronically ill schizophrenia patients and 16
age-matched control subjects. All of the schizophrenia subjects were being
treated with antipsychotic medications, but most evidence to date suggests
that antipsychotic medications have little impact on memory. Also, structural
changes in the hippocampus have been noted from the earliest stages of
psychosis, suggesting that they are not caused by antipsychotic drugs.
First, Weiss and his team used high-resolution magnetic resonance imaging
(MRI) to measure hippocampal size in their schizophrenia and control subjects.
They found that the hippocampus in both the left and right hemispheres of the
brain was significantly smaller in the schizophrenia subjects than in the
Then the researchers gave the subjects a word-recognition task and used
functional magnetic resonance imaging (fMRI) to see how the subjects'
hippocampi responded during this task.
Both the schizophrenia subjects and the control subjects performed
similarly on this task, and their hippocampi did, too—that is, there was
considerable activation of the hippocampus in both the left and right
hemispheres of the brain in both subject groups during this memory task.
Then the investigators gave the subjects a task in which they had to
determine which words they had seen before and which they had not. Again fMRI
was used to assess the activity of their hippocampi during the task. But this
time, the schizophrenia subjects did not perform the task as well as the
controls, having a greater tendency to indicate that they had seen an item not
previously presented. Also, whereas the right hippocampus of the control
subjects was activated during the task, the right hippocampus of the
schizophrenia subjects was not.
Finally, the researchers examined the relationship between decreased
hippocampal volume, impaired memory performance, and abnormal hippocampal
function in the schizophrenia subjects. As they pointed out in their study
report, they made an "intriguing finding—the volume of the right
hippocampus was inversely correlated with the false-alarm rate in the
schizophrenia group." Also, they added, "these findings are
consistent with previous work in patients with schizophrenia indicating
heightened rates of false alarms during tests of verbal memory."
Two conclusions can be drawn from these findings, Weiss and his team
believe. For one, even though schizophrenia patients have a small hippocampal
volume, it does not seem to lead to across-the-board memory difficulties.
Nonetheless, having a small hippocampus does appear to make it difficult for
schizophrenia patients to recognize novel items.
The study was funded by the National Institute of Mental Health, Mental
Illness and Neuroscience Discovery Institute, and National Alliance for
Research on Schizophrenia and Depression Young Investigator Awards. ▪