Only now do we begin to understand why we spend a third of our lives sleeping. And it turns out that our memory is far from being inactive during this time.
New Memory Traces are Created While We Are Asleep
Interestingly, in sleep, an offline reactivation of the newly recorded memory tracks occurs in the waking state. It has been demonstrated both in intracerebral leads in animal experiments and activation patterns in human imaging. The idea here is that this reactivation contributes to a strengthening of the initially fragile traces of memory so that these are subsequently better available for retrieval. However, increasing the overall transmission strength at the synapses has a price in the form of:
- Increased energy demand
- Increased space requirements
- Degradation of the signal-to-noise ratio due to saturation phenomena.
An increasingly well-researched issue indicates that the necessary down-regulation of the overall strength of synapses predominantly takes place during sleep. Specifically, the typical neuronal firing pattern of intense activity and inactivity, which occurs only in a deep sleep and becomes recognizable as slow oscillations in the surface derivation of the brain waves, allows for the described synaptic downscaling.
This downscaling can be seen as a prerequisite that a new recording of information is possible again. There are assumptions that the initially opposing processes of synaptic strengthening through reactivation and downscaling by slow oscillations occur in parallel, finely orchestrated.
There are two major memory systems:
- The declarative memory
- The non-declarative memory
There are new memory traces on the behavioral level in those.
Sleep Disorders Can Disrupt Memory Activity
It is experimentally challenging and yet conclusively clarified what proportion actually sleep-specific brain activity compared to the simple reduction of external stimuli in sleep has. Patients with persistent sleep disturbances in the form of chronic insomnia or sleep apnea syndrome show a decrease in sleep-related memory consolidation compared to healthy sleep subjects. How frequently do you lie in bed and cannot sleep because of an upcoming test of thought on where to buy essays cheap?
To what extent improvement of sleep by treatment also leads to a development in sleep-related memory formation is currently unclear. A significant finding, however, stays that although the most widely used group of hypnotics can increase sleep duration, they significantly impede synaptic plasticity processes in animal experiments and memory formation in animals and humans.
Of interest is the question of whether sleep can be targeted or modulated to promote memory formation and neuronal plasticity. The simplest procedure is the establishment of additional sleep phases in the form of an afternoon nap. Some studies show that even short sleep periods of 30 minutes and possibly even shorter are sufficient to strengthen previously learned memory traces.
Influence of afternoon nap and continuous load
In a recent study, there was a paradigm of transcranial magnetic stimulation for inducing LTP-like plasticity on the human cortex and showing that the consolidation of this form of plasticity in healthy volunteers is enhanced by a nap compared to a waking phase. Other work has indicated that performance degrades under continuous stress. For example, in a pattern recognition task, is restored through sleep rather than a quiet waking phase. It is for our everyday life, but certainly for high-performance areas:
- Professional music performances
- Sports and activities
- Difficult tasks at work
- Things of interest
Activities of interest, in particular, show that memory traces can be specifically strengthened during sleep.
Conversely, we are currently investigating to what extent a selective suppression of slow oscillations could mimic the well-documented therapeutic effect of sleep deprivation in patients with severe depressive episodes (“sleep deprivation light”). Further, potential clinical relevance is the first study showing that a targeted sleep phase can enhance the effectiveness of psychotherapy. The goal here is to augment the learning process that underlies successful psychotherapy. All these approaches are shown in individual studies, but currently without sufficient evidence of clinical efficacy.
Memory Is Not an Exact Copy of the Information
In addition to the described simple quantitative strengthening, our memory is also characterized by a qualitative reorganization. By this, we mean that our mind is not an exact copy of the information, but a reconstruction that depends on existing schemata. Famous are the observations of Sir Frederic C. Bartlett (1886-1969, a Psychology professor in Cambridge), the beginning of 1930 subjects told the Indian myth “war of ghosts,” which contains certain inconsistencies. For example, in this myth, Indians go hunting seals to the river.
Many subjects recalled from days to months that the Indians went fishing on a river. So they had adapted the foreign image to their own culture and thus normalized it. A fascinating idea is that especially REM sleep (the sleep phase characterized by rapid eye movements and a particularly high brain and dream activity) is a condition of the brain that not only allows a simple strengthening as assumed in NREM sleep but a cross-linking and reorganization that can be considered a prerequisite for new insights and creativity.
Neurobiologically, this would be plausible, because, in REM sleep, the external perception is largely suppressed. However, there is a strong generation of feelings instead of reduced cognitive control. Besides, the idea is based on old ideas about the function of dreams, in which there is an unconscious (re) activation and processing of content. Despite all the charm of this idea, the experimental data is inconsistent.
For example, in a separate study that used a word problem as an index for the reorganization of memory and creativity, sleep that contained REM sleep did not result in increased memory reorganization. One possible explanation is that true creativity is an experiment that is difficult to plan and difficult to investigate.
Despite certain limitations, it currently appears that possible sleep effects on memory reorganization are small and less robust than those on quantitative strengthening. Perhaps sleep, along with other functions, is a price we pay for the basic process of neuronal plasticity that cannot be completed while we’re awake.