Nightmares, often described as frightening dreams that evoke feelings of terror, fear, distress, or anxiety, have been a topic of human curiosity for centuries. As far back as 1721, dictionaries defined nightmares as dreams causing unease, highlighting their long-recognized impact on our sleep and emotions. While we might use the term colloquially to describe unpleasant experiences, for a significant portion of the population, especially children, nightmares are a vivid and sometimes disturbing reality.
It’s estimated that between 3 to 7 percent of adults in the U.S. experience nightmares as a recurring problem. However, these vivid bad dreams are more commonly reported in children, particularly those aged 3 to 6. Deirdre Barrett, PhD, an assistant clinical professor of psychology at Harvard Medical School, suggests an evolutionary perspective on this phenomenon. “Children are smaller and are vulnerable to many more threats than adults,” she explains. “Nightmares may partially reflect this vulnerability,” potentially serving as a way for the developing brain to process fears and prepare for potential dangers.
Dreams themselves are understood as the brain’s way of processing recent autobiographical events, weaving them together with past memories to form new memory pathways. Nightmares, in this context, are essentially dreams that trigger a strong negative emotional response. These dream experiences occur within the brain’s default network, a system of interconnected brain regions including the thalamus, medial prefrontal cortex, and posterior cingulate cortex. This network remains active during periods of rest and quiet reflection, including sleep.
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One such quiet period crucial for dreaming is REM (Rapid Eye Movement) sleep. REM sleep is a distinct stage characterized by rapid eye movements, irregular heartbeat, and increased respiration rate. It occurs in several episodes throughout the night, making up approximately 20 percent of our total sleep time. During these REM cycles, the brain’s default network is highly active, and it is within these periods that we experience the most vivid and memorable dreams, including nightmares.
Nightmares are more likely to occur during the later portion of sleep, when REM sleep intervals tend to lengthen, typically in the latter half of the night. As we approach wakefulness, the brain begins to consolidate and integrate memories. Dreaming often happens as we transition out of REM sleep, on the cusp of waking. This timing is why nightmares, with their intense and often terrifying imagery, are more easily recalled compared to other dreams.
Understanding the Difference: Nightmares vs. Night Terrors
A man experiencing distress from a nightmare, sitting on the edge of his bed with a scared expression.
Nightmares are frequently confused with night terrors, although they are distinct sleep phenomena. Night terrors are more common in children and are often more dramatic and outwardly visible than nightmares. Crucially, night terrors are not considered dreams in the traditional sense. Instead, they are sudden fear reactions that arise during transitions between different sleep stages, specifically when moving from deep non-REM sleep to lighter REM sleep, typically two to three hours after falling asleep. During a night terror, a child might exhibit physical signs of fear, such as kicking, screaming, and thrashing. However, because night terrors occur during non-REM sleep, a period of less active brain function in terms of narrative dreaming, children usually have no memory of the event upon waking.
Dr. Barrett clarifies this difference: “Night terrors are a phenomenon of the deepest parts of non-REM sleep, when the brain is less active. In a night terror, a child awakens with heart pounding. There is, however, either no content to the feeling of terror or there is a simple scary image. There is not, however, the sort of narrative story you experience with dreams, including nightmares.” John Winkelman, AM ’83, MD ’87, PhD ’83, an HMS associate professor of psychiatry specializing in sleep disorders at Massachusetts General Hospital, further explains that this lack of memory is due to night terrors originating during short-wave sleep. Short-wave sleep is characterized by reduced activity in the neocortex, the brain’s center for higher-level mental functions, which is essential for memory formation and detailed dream narratives.
In summary, while both nightmares and night terrors are sleep disturbances that can cause fear and distress, nightmares are vivid, frightening dreams occurring during REM sleep that are typically remembered, while night terrors are non-REM sleep events characterized by intense fear reactions with little to no dream recall. Understanding these distinctions is key to addressing sleep-related anxieties and promoting healthier sleep patterns.
