Dreaming and the hippocampus: research identifies a brain region that is crucial for enabling us to dream
Research led by Dr Goffredina Spanò from the Memory and Space Team at the Wellcome Centre for Human Neuroimaging have found that damage to the hippocampus (a part of the brain that plays an important role in learning and memory) may have an effect on dreaming. Their findings have been reported in a recent paper in eLife: Dreaming with hippocampal damage.
Dreaming has intrigued humans for thousands of years, yet it is currently unknown exactly why it occurs. Although dreams are not a precise replay of our memories, it is thought that one potential function of dreaming could be to assist with the offline processing of our past experiences. The hippocampus is a part of the brain known to be critical for supporting memories, and damage to it can cause amnesia – the inability to form new memories and recall the past episodes that punctuate our lives. Yet whether hippocampal damage affects dreaming is an open question. If it does, this would reinforce the link between dreaming and memory, potentially moving us closer to an understanding of why we dream.
Studying dreaming is challenging. Asking people (especially those with amnesia), in the morning whether or not they dreamed the night before is not ideal, because they may have dreamed but forgotten. Instead, a provoked awakening protocol can be used to probe dreams more directly. This approach, which was used in the current study, involves waking people up at various times during their night’s sleep to report their thoughts in that moment.
The researchers found that a rare group of patients with selective bilateral hippocampal damage dreamed much less than a matched control group of healthy individuals. This was despite both groups being woken up a similar number of times. The study also revealed that the few dreams the patient group had lacked detail and content.
These findings suggest that having healthy hippocampi may be essential in order for typical dreaming to occur. Damage to this brain structure is common in a number of conditions, including dementia. If dreaming is compromised, this may worsen the memory deficits known to be associated with such conditions.
Senior author, Professor Eleanor Maguire, reflects on the findings:
“The question has long been asked whether or not people with amnesia dream. We’re grateful to our participants who enabled us to find out that dreaming is degraded in the context of hippocampal damage and amnesia. This exciting finding tells us more about the functions of the hippocampus, and also provides further clues about why we dream”
The full paper is published in eLife: Dreaming with hippocampal damage.