Our most vivid dreams are a remarkable replication of reality, combining disparate objects, actions and perceptions into a richly detailed hallucinatory experience.
How does our brain accomplish this? It has long been suspected that the hippocampus contributes to dreaming, in part due to its close association with memory: according to one estimate, about half of all dreams contain at least one element originating from a specific experience while the subject was awake Fosse et al. Although these dreams are rarely a faithful replication of any one memory, fragments of various recent experiences intermingle with other memories usually related remote and semantic memories to create a novel dream.
Given all this, one might guess that dreams are created by those regions of the brain responsible for memory. However, studies dating back to the s have suggested that patients with a damaged hippocampus still dream Torda, a ; Torda, b ; Solms, and, somewhat amazingly, such patients can have dreams involving recent experiences of which they have no conscious memory Stickgold et al.
Or alternatively, might such damage, while not preventing dreams, alter the form in which they are expressed? Indeed, there is reason to think that the hippocampus supports crucial aspects of dream construction beyond the simple insertion of memories. Recent work in the cognitive neurosciences has established that the hippocampus, in addition to being involved in the formation of memories, is also part of a brain system that is involved in using memory to construct novel imagined scenarios and simulate possible future events Hassabis et al.
As a result, patients without a hippocampus find it difficult to imagine scenes that are coherent, possibly because the hippocampus is responsible for combining different elements of memory into a spatially coherent whole. Besides reporting substantially fewer dreams than the patients in a control group, the four patients with amnesia also reported dreams that were markedly less detailed: their dreams contained fewer details of spatial location e.
These observations support the emerging view that dreams are generated by networks in the brain similar to the networks that are involved in recalling memories and constructing imagined scenarios during wakefulness Fox et al.
Like memory and imagination, a vivid dream requires the construction of detailed, memory-based imagined scenes — and this process appears to rely on the hippocampus. This allows us to confidently attribute their impoverished dreams to the loss of the hippocampus itself, rather than to other regions of nearby temporal lobe which might also have a role in dreaming.
As with many studies of rare neurological patients, the latest work must be interpreted with caution due to the small sample size. For example, patient dreams were not significantly shorter than control dreams, leading to an apparently selective deficit in specific types of details reported such as spatial details and sensory details , rather than a general deficit in the length of the dream.
Views Annotations Open annotations. The current annotation count on this page is being calculated. Image credit: Public domain CC0. Related to. Sign up for email alerts Privacy notice. This wakefulness is another must-have component of memory formation.
And brief periods of awakenings — around two minutes — is enough time for dreams to be encoded into long term memory, the paper explained. When it comes to intellectual gymnastics, grey matter drives performance. Gray matter makes up about half of our brains, with white matter making up the other half. If you think of a brain as a computer, gray matter would represent the information processing systems. And white matter would act as the cables that connect these different components together, allowing brain communication to flow.
Vallat and a research team found that people who frequently remember dreams have more white matter in a region of the brain known as the medial prefrontal cortex, which is a brain region linked with processing information about oneself. This finding is yet another piece of evidence that shows brain connectivity is somehow important in dream recall.
But having more white matter may not just help you remember your dreams, it may also promote dream creation. As prominent neuropsychologist Mark Solms found in the early s , people who developed rare, brain-damaging lesions within the white matter of the medial prefrontal cortex reported that they stopped dreaming altogether. Another interpretation is that they stopped dreaming. But for most people, much of dream recall boils down to individual characteristics — some within our control, and some not.
Scientists also know that women , on average, are more likely to remember their dreams than men. Teenage boys are less encouraged to speak about their dreams or feelings. But both sexes may notice that their ability to remember our dreams seems to fade with age. As we grow older, our sleep patterns tend to change. Older people get less slow wave sleep, often referred to as deep sleep. Between the ages of 20 and 60, deep sleep decreases at a rate of 2 percent per decade.
But the amount of REM sleep, when our most memorable dreams seem to occur, stays about the same. Do age-related changes make much of a difference when it comes to dream recall? Vallat said probably not. Instead, day-to day stressors like deadlines, bills and appointments often take precedence over our dream worlds. And people may miss out on REM sleep by cutting sleep short.
0コメント