Declarative memory is the memory for conscious events. There are two types of declarative memory: episodic and semantic. Episodic memory is for remembering experiences whereas semantic memory is remembering specific facts.
Temporal memory consists of remembering when a specific memory has occurred. In study participants were placed in 4 groups; two control groups either given caffeine or a placebo and two groups that were sleep deprived for 36 hours either given caffeine or a placebo. The task used to measure temporal memory consisted of discriminating between recent and less recent face presentations. A set of twelve unfamiliar faces were presented sequentially every 10 seconds. A self-ordered pointing task was used afterward for 5 minutes to prevent rehearsal and to keep tired participants occupied. This required them to mark any new items seen (either nouns or abstract shapes) presented on 12 sheets. A second set was presented, followed by another self-ordered pointing task, and then a random sequence of 48 faces either containing previously presented faces or new ones were shown to the participant. They were asked if they recognized the faces and whether they were from the first or second set. Results indicate that sleep deprivation does not significantly affect recognition of faces, but does produce a significant impairment of temporal memory (discriminating which face belonged to which set). Caffeine was found to have a greater effect on the sleep-deprived group as compared to the placebo group deprived of sleep but still performed worse than both control groups. Sleep deprivation was also found to increase beliefs about being correct, especially if they were wrong. Brain imaging studies of those sleep-deprived found that the greatest reduction in metabolic rate is in the prefrontal cortex.
Cerebral activation during performance on three cognitive tasks (verbal learning, arithmetic, and divided attention) was compared after both normal sleep and 35 hours of total sleep deprivation (TSD) in a study by Drummond and Brown. Use of fMRI measured these differences in the brain. In the verbal learning task, fMRI indicated the regions involved in both verbal learning and memorization. The results found that both TSD and a normal night of sleep showed a significant response in the prefrontal cortex and following TSD displayed a response of additional areas which included other prefrontal areas, bilateral inferior parietal lobule and superior parietal lobes. Increases in sleepiness also correlated with activation of two ventral prefrontal regions and a correlation between a greater activation in bilateral parietal lobes (which include language areas) and lower levels of impairment on free recall were also found following TSD. In the arithmetic task normal sleep showed the expected activation in the bilateral prefrontal and parietal working memory regions but following TSD only showed activation in the left superior parietal lobe and the left premotor cortex in response, with no new areas to compensate (as was found in verbal learning).
Increased sleepiness was correlated with activation in a ventral prefrontal region, but only one region. The divided attention task combined both verbal learning and the arithmetic task. fMRI indicated that cerebral response after TSD is similar to that of the verbal learning task (specifically the right prefrontal cortex, bilateral parietal lobes, and cingulate gyrus showing the strongest response). The implication of this finding is that additional brain regions activated after both verbal learning and divided attention tasks following TSD represent a cerebral compensatory response to lacking sleep.
For example, there is a decline in the response of the left temporal lobes during both tasks which are involved in different learning tasks during a rested state but the involvement of the left inferior parietal lobe in short-term verbal memory storage following TSD suggests that this region might compensate. No new areas for the arithmetic task may suggest that it relies heavily on working memory so compensation is not possible, in comparison to tasks such as verbal learning which rely less on working memory.
Implicit face memory
Faces are an important part of one’s social life. To be able to recognize, respond and act towards a person requires unconscious memory encoding and retrieval processes. Facial stimuli are processed in the fusiform gyrus (occipitotemporal brain area) and this processing is an implicit function representing a typical form of implicit memory. REM sleep has been seen to be more beneficial to implicit visuospatial memory processes, rather than slow-wave sleep which is crucial for explicit memory consolidation. REM sleep is known for its visual experiences, which may often include detailed depictions of the human countenance. A recognition task was used to gauge familiarity with a previously shown sequence of faces after a subsequent period of REM sleep. It was seen that the fusiform gyrus was active during training, the REM sleep period, and the recognition task as well. It is hypothesized that brain mechanisms during REM sleep, as well as pure repetition priming, can account for the implicit recognition of the previously shown faces.
For centuries people have pondered the meaning of dreams. While there has always been a great interest in the interpretation of human dreams, it wasn’t until the end of the nineteenth century that Sigmund Freud and Carl Jung put forth some of the most widely-known modern theories of dreaming.
Since then, technological advancements have allowed for the development of other theories. One prominent neurobiological theory of dreaming is the “activation-synthesis hypothesis,” which states that dreams don’t actually mean anything: they are merely electrical brain impulses that pull random thoughts and imagery from our memories. Humans, the theory goes, construct dream stories after they wake up, in a natural attempt to make sense of it all.
Cristina Marzano and her colleagues at the University of Rome have succeeded, for the first time, in explaining how humans remember their dreams. The scientists predicted the likelihood of a successful dream recall based on a signature pattern of brain waves. In order to do this, the Italian research team invited 65 students to spend two consecutive nights in their research laboratory.
This finding is the increased frontal theta activity the researchers observed looked like the successful encoding and retrieval of autobiographical memories seen while awake. That is, it is the same electrical oscillations in the frontal cortex that make the recollection of episodic memories possible. Thus, these findings suggest that the neurophysiological mechanisms that people employ while dreaming (and recalling dreams) are the same as when they construct and retrieve memories while awake.
In another recent study conducted by the same research team, the authors used the latest MRI techniques to investigate the relationship between dreaming and the role of deep-brain structures. In their study, the researchers found that vivid, bizarre and emotionally intense dreams (the dreams that people usually remember) are linked to parts of the amygdala and hippocampus. While the amygdala plays a primary role in the processing and memory of emotional reactions, the hippocampus has been implicated in important memory functions, such as the consolidation of information from short-term to long-term memory.
The proposed link between dreams and emotions is highlighted in another study published by Matthew Walker and colleagues at the Sleep and Neuroimaging Lab at UC Berkeley, who found that a reduction in REM sleep (or less “dreaming”) influences the ability to understand complex emotions in daily life – an essential feature of human social functioning. Scientists have recently identified where dreaming is likely to occur in the brain. A very rare clinical condition known as “Charcot-Wilbrand Syndrome” has been known to cause (among other neurological symptoms) loss of the ability to dream. However, it was not until a few years ago that a patient reported having lost her ability to dream while having virtually no other permanent neurological symptoms. The patient suffered a lesion in a part of the brain known as the right inferior lingual gyrus (located in the visual cortex). Thus, now it is known that dreams are generated in, or transmitted through this particular area of the brain, which is associated with visual processing, emotion, and visual memories.
Dreams seem to help to process emotions by encoding and constructing memories of them. What is seen and experienced in dreams might not necessarily be real, but the emotions attached to these experiences certainly are. The dream stories essentially try to strip the emotion out of a certain experience by creating a memory of it. This way, the emotion itself is no longer active. This mechanism fulfills an important role because when emotions are not processed, especially negative ones, this increases personal worry and anxiety. Severe REM sleep-deprivation is increasingly correlated with the development of mental disorders. In short, dreams help regulate traffic on that fragile bridge which connects experiences with emotions and memories.
Sleep is important in the aging process as many chemical, biological and psychological processes take place during the resting period. Good sleep is a primary factor for healthy aging.