External sensory stimuli that awaken a person from sleep

An external sound or touch can awaken someone.

Can a light? It would have to be very strong, but part of the reason might be that it would have to penetrate the eyelids.

And can a smell or taste?

When we are awake, the impact of sensory stimuli and of changes in them depend on which sense is stimulated.

My question concerns the kind and strength of impact the stimulation of each sense has when we are asleep, in relation to what is needed to wake us up.


Thanks to @Mithoron for linking to another question, asked on this website by @Taladris. That question is certainly quite similar to this one and its answer contains some relevant material, even if the answer is not of high quality because of course our senses are "dimmed" when we are asleep and of course it is not true that "that we respond to our own names in a similar fashion in sleep and in wakefulness". The present question asks specifically about awakening because of sensory input. I believe I am sometimes awakened by smells, although it is hard for me to tell whether or not I am right. Part of my question asks for views or facts concerning whether people can be woken by smells at all. This is different from asking whether we can smell when we are asleep.

Brain Listens During Sleep

Tanya Lewis
Jun 15, 2016

ISTOCK PHOTO, MARTINWIMMER The human brain may wind down when asleep, but it doesn&rsquot lose all responsiveness. Researchers from the École Normale Supérieure in Paris and their colleagues recently used electroencephalography (EEG) to monitor the brains of volunteers listening to recordings of spoken words, which they were asked to classify as either objects or animals. Participants were able to classify words during light non-REM (NREM) sleep, but not during either deep NREM sleep or REM sleep, according to a study published today (June 14) in The Journal of Neuroscience.

&ldquoWith an elegant experimental design and sophisticated analyses of neural activity, [the authors] demonstrate the extent to which the sleeping brain is able to process sensory information, depending on sleep depth [or] stage,&rdquo Thomas Schreiner of the University of Fribourg in Switzerland, who was not involved in the study, wrote in an email to The Scientist.

“When we fall asleep, it’s pretty similar to a coma because we lose consciousness of our self and of the [outside] world,” study coauthor Thomas Andrillon, a neuroscientist at the École Normale Supérieure, told The Scientist. The question was “whether the brain could still monitor what was going on around, just to be sure the environment was still safe,” he added.

The present study followed on a 2014 study, in which the researchers performed similar assessments while participants took daytime naps. As part of that project, Andrillon and colleagues had people listen to spoken words in French and push a button with their left or right hand to indicate if the word was an object or animal, respectively, as the volunteers fell asleep. Meanwhile, the researchers measured the participants’ EEG brain activity looking for evidence that the motor cortices were preparing to make button-pushing movements.

For the present study, in which participants remained in the lab overnight, the researchers divided the sleep into three stages: REM, light NREM, and deep NREM. During REM sleep, the volunteers continued to mentally prepare finger movements during the word task as if they were awake, but only if they had encountered and categorized the words previously. During light NREM, the participants still showed motor preparation no matter whether the words were novel or had been presented before. And in deep NREM, the participants did not show any brain activity associated with button-pushing, Andrillon and colleagues found. The findings are in line with those of previous behavioral studies.

The researchers proposed mechanisms by which sensory information might be gated during REM and deep NREM sleep. In the former, information from the outside world may compete with (internally generated) dreams in the latter, the brain experiences waves of hypersynchrony, in which “hundreds of thousands of neurons are going silent at the same time,” preventing the brain from processing sensory information, Andrillon explained.

“Andrillon [and colleagues] confirm their previous results showing that a complex processing of external information—semantic integration and task-related motor preparation—is possible in light NREM sleep,” Mélanie Strauss, a neurologist at the Hôtel-Dieu hospital in Paris who was not involved in the study, wrote in an email to The Scientist. “But they also demonstrate that this processing is disrupted in other sleep stages, in deep NREM sleep and, maybe more surprisingly, in REM sleep,” she added.

The idea that the brain can selectively process information from the outside world during sleep is not new. A recent study found that during the first night spent in a new environment, one brain hemisphere remains active to “keep watch.”

“When you sleep, if there is relevant information in the environment, it can modulate vigilance,” Andrillon said.

T. Andrillon et al., Neural markers of responsiveness to the environment in human sleep,” Journal of Neuroscience, doi:10.1523/JNEUROSCI.0902-16.2016, 2016.

What Are Some Examples of External Stimuli?

Examples of external stimuli include changes in temperature, sights, sounds, tastes, and smells that can affect the body and the mind. External stimuli affect one from the outside - anything that touches upon one of the five senses.

External stimuli can affect a person's decision-making abilities and choices. For example, when a person is hungry and sees a slice of pizza, internal stimuli from within the body, such as a stomach growl, salivating and hunger pain, indicates the need for food the external factor, the pizza slice that a person is viewing through sight, serves as the external stimuli.

Other examples of external stimuli include television and commercial ads, a window display at a clothing store, or a recommendation of a product. These examples all invoke one or more of the five senses.

External stimuli can also affect a person's ability to perform with focused concentration. For example, when playing a sport, factors such as rain or snow can impede an athlete's physical abilities. Hostile crowds, poor field conditions and unfair calls by officials also serve as external stimuli that can either derail or further motivate an athlete. Negative thoughts and self-talk that affect performance are examples of internal stimuli.

Problems with Circadian Rhythms

Generally, and for most people, our circadian cycles are aligned with the outside world. For example, most people sleep during the night and are awake during the day. One important regulator of sleep-wake cycles is the hormone melatonin. The pineal gland, an endocrine structure located inside the brain that releases melatonin, is thought to be involved in the regulation of various biological rhythms and of the immune system during sleep (Hardeland, Pandi-Perumal, & Cardinali, 2006). Melatonin release is stimulated by darkness and inhibited by light. People rely on zeitgebers, or external cues, such as light, atmospheric conditions, temperature, and social interactions, to set the appropriate biological clock.

There are individual differences in regard to our sleep-wake cycle. For instance, some people would say they are morning people, while others would consider themselves to be night owls. These individual differences in circadian patterns of activity are known as a person’s chronotype. A person’s individual chronotype may show that a person has a greater propensity to sleep earlier and wake up earlier (a morning lark), or to stay up late and sleep in (a night owl). Morning larks and night owls differ with regard to sleep regulation (Taillard, Philip, Coste, Sagaspe, & Bioulac, 2003). Sleep regulation refers to the brain’s control of switching between sleep and wakefulness as well as coordinating this cycle with the outside world.

Link to Learning

Watch this brief video describing circadian rhythms and how they affect sleep.

Can a Person Learn While Sleeping?

Some studies show it is possible to learn new information during sleep, such as new vocabulary in a foreign language.

For most people, the 16 hours spent awake each day are hardly enough time to get critical tasks done, let alone acquire knowledge. Yet a growing number of neuroscientists believe that sleep not only helps cement memories, but is actually a time to learn something new—even a foreign language.

Sanam Hafeez, a clinical neuropsychologist and professor at Columbia University, explains how this might be possible.

Learn This Word: Hypnopedia

Through decades of research, Dr. Hafeez says, scientists have concluded that while we’re bombarded by stimuli all day, sleep is the time when the brain filters all that information. “I think of it as a computer shuffling process: junk, junk, junk, important, junk,” she says. “As it tunes out all these distractions, the brain encodes information and decides how important a memory or a piece of information is.”

A study published in 1965 using electroencephalograms (EEGs) showed that hypnopedia, or sleep-learning, was a real thing. In that and later studies, researchers showed that during certain cycles of sleep that don’t include dreaming, the hippocampus—the primary area of the brain related to memory and learning, as well as in the retrieval of new learning—is activated.

This happens, Dr. Hafeez says, through “neural oscillatory activity,” or the up-and-down of wakefulness that occurs during Stage 2 non-REM sleep, when the heart rate slows and body temperature drops. The “up-down” moments of neural activity, called sleep spindles, last half a second to two seconds and have been shown to play an essential role in sensory processing and long-term consolidation of memory.

How do we disconnect from the environment during sleep and under anesthesia?

During sleep and under anesthesia, we rarely respond to such external stimuli as sounds even though our brains remain highly active.

Now, a series of new studies by researchers at Tel Aviv University's Sackler Faculty of Medicine and Sagol School of Neuroscience find, among other important discoveries, that noradrenaline, a neurotransmitter secreted in response to stress, lies at the heart of our ability to "shut off" our sensory responses and sleep soundly.

"In these studies, we used different, novel approaches to study the filtering of sensory information during sleep and the brain mechanisms that determine when we awaken in response to external events," explains Prof. Yuval Nir, who led the research for the three studies.

The first study, published in the Journal of Neuroscience on April 1 and led by TAU doctoral student Yaniv Sela, calls into question the commonly accepted idea that the thalamus -- an important relay station for sensory signals in the brain -- is responsible for blocking the transmission of signals to the cerebral cortex.

"The shutdown of the thalamic gate is not compatible with our findings," says Sela whose study compares how neurons in different brain regions respond to simple and complex sounds while asleep or awake.

Using rat models, he found that the responses of neurons in the auditory cortex were similar when the rodents were awake or asleep. But when he examined the perirhinal cortex, related to complex conscious perception and memory associations, he found that neurons showed much weaker responses during sleep.

"Basic analysis of sound remains during sleep, but the sleeping brain has trouble creating a conscious perception of the stimulus," Sela adds. "Also, while we found that initial and fast responses are preserved in sleep, those that occur later and require communication between different regions in the cortex are greatly disrupted."

The second study, published on April 8 in Science Advances, finds that the locus coeruleus, a tiny region of the brainstem and the main source of noradrenaline secretions in the brain, plays a central role in our ability to disconnect from the environment during sleep. Led by TAU doctoral student Hanna Hayat at Prof. Nir's lab, the research was conducted in collaboration with Prof. Tony Pickering of Bristol University, Prof. Ofer Yizhar of the Weizmann Institute and Prof. Eric Kremer pf the University of Montpellier.

"The ability to disconnect from the environment, in a reversible way, is a central feature of sleep," explains Hayat. "Our findings clearly show that the locus coeruleus noradrenaline system plays a crucial role in this disconnection by keeping a very low level of activity during sleep."

For the purpose of the research, the scientists used rat models to determine the level of locus coeruleus activity during sleep and which sounds, if any, would be responsible for waking up the rodents.

They found that the rats' varying levels of locus coeruleus activity accurately predict if the animals would awaken in response to sounds. The team then silenced the locus coeruleus activity through optogenetics, which harnesses light to control neuronal activity, and found that the rats did not readily awaken in response to sound.

"When we increased the noradrenaline activity of the locus-coeruleus while a sound played in the background, the rats woke up more frequently in response, but when we decreased the activity of the locus coeruleus and played the same sound in the background, the rats only rarely woke up," says Hayat. "So we can say we identified a powerful 'dial' that controls the depth of sleep despite external stimuli.

"Importantly, our findings suggest that hyperarousal in some individuals who sleep lightly, or during periods of stress, may be a result of continued noradrenaline activity during sleep when there should only be minimal activity."

The third study, published on May 12 in the Proceedings of the National Academy of Sciences (PNAS), led jointly by TAU doctoral student Dr. Aaron Krom of Hadassah Hebrew University Medical Center and TAU doctoral student Amit Marmelshtein, focuses on our response to anesthesia and finds that the most significant effect of loss-of-consciousness is the disruption of communication between different cortical regions.

The study was the fruit of a collaboration between Prof. Nir, Prof. Itzhak Fried and Dr. Ido Strauss of TAU's Sackler Faculty of Medicine and Tel Aviv Sourasky Medical Center, and a team at Bonn University.

"Despite the routine use of anesthesia in medicine, we still do not understand how anesthesia leads to loss of consciousness this is considered a major open question in biomedical research," explains Dr. Krom.

For the research, the scientists recorded the brain activity of epilepsy patients who had previously shown little to no response to drug interventions. The patients were hospitalized for a week and implanted with electrodes to pinpoint where in the brain their seizures originated. They were then anesthetized for the removal of their electrodes and their neuron activity recorded while they listened to sounds through headphones. They were asked to perform a task until they lost consciousness, which allowed the researchers to examine how their brain activity changed, down to individual neurons, in response to sounds at the very moment they lost consciousness.

"We found that loss-of-consciousness disrupted communication between cortical regions such that sounds triggered responses in the primary auditory cortex, but failed to reliably drive responses in other regions of the cortex," adds Marmelshtein. "This is the first study to examine how anesthesia and loss of consciousness affect sensory responses at a resolution of individual neurons in humans. We hope that our results will guide future research, as well as attempts to improve anesthesia and develop instruments that can monitor the level of consciousness in anesthesia and other states of altered consciousness such as vegetative states and severe dementia."

"These studies advance our understanding of sensory disconnection during sleep and anesthesia," concludes Prof Nir. "Sleep disturbances are a major health issue and are frequent in aging, as well as in neurological and psychiatric disorders. It is important to test if our findings on varying noradrenaline levels can explain hyperarousal that characterizes condition such as anxiety disorders and PTSD, and if so to build on these findings to develop novel methods to improve sleep quality."

I Keep a Close Watch on This Heart of Mine: Increased Interoception in Insomnia

Study objectives: Whereas both insomnia and altered interoception are core symptoms in affective disorders, their neural mechanisms remain insufficiently understood and have not previously been linked. Insomnia Disorder (ID) is characterized by sensory hypersensitivity during wakefulness and sleep. Previous studies on sensory processing in ID addressed external stimuli only, but not interoception. Interoceptive sensitivity can be studied quantitatively by measuring the cerebral cortical response to one's heartbeat (heartbeat-evoked potential, HEP). We here investigated whether insomnia is associated with increased interoceptive sensitivity as indexed by the HEP amplitude.

Methods: Sixty-four participants aged 21-70 years were recruited through including 32 people suffering from ID and 32 age- and sex-matched controls without sleep complaints. HEPs were obtained from resting-state high-density electroencephalography (HD-EEG) recorded during evening wakeful rest in eyes-open (EO) and eyes-closed (EC) conditions of 5-minute duration each. Significance of group differences in HEP amplitude and their topographical distribution over the scalp were assessed by means of cluster-based permutation tests.

Results: In particular during EC, and to a lesser extent during EO, people with ID had a larger amplitude late HEP component than controls at frontal electrodes 376-500 ms after the R-wave peak. Source localization suggested increased neural activity time-locked to heartbeats in people with ID mainly in anterior cingulate/medial frontal cortices.

Conclusions: People with insomnia show insufficient adaptation of their brain responses to the ever-present heartbeats. Abnormalities in the neural circuits involved in interoceptive awareness including the salience network may be of key importance to the pathophysiology of insomnia.

Keywords: event-related potential heartbeat-evoked potential high-density EEG hyperarousal insomnia disorder interoception resting state salience network.

What Is a Sensory Deprivation Tank Used For?

Sensory deprivation tank is relaxation therapy. It is known to help individuals suffering from chronic stress, work-related muscle pains, and gastric upsets and burn out. It may also be used for those dealing with insomnia or other sleeping disorders. Sensory deprivation, or restricted environmental stimulation therapy (REST), is a technique by which sensory input (sound, light, smell, etc.) is minimized. This practice encourages an extremely deep level of relaxation. REST is typically conducted in a float tank, in which the person is suspended in a solution of warm water and Epsom salt without sound or light.

This condition is known to evoke a relaxation reflex (RR). This reflex is the opposite of the "flight or fright&rdquo response seen in dealing with stress. RR has a direct effect on the parasympathetic system (part of the brain responsible for relaxation) and causes many positive effects on the body systems.

An hour in a float tank can serve as a power nap that leaves an individual completely refreshed and energized. An hour of floating equals as much as eight hours of normal sleep.

  • The sensory deprivation tank may also help to ease muscle tensions and mental anxieties. This may be due to the complete cessation of stimuli of sound and sight. Furthermore, the elimination of gravity on the body allows the muscles and joints to release tension and get rid of soreness. For this reason, people suffering from musculoskeletal and rheumatic conditions greatly benefit from floatation REST.
  • It provides an unparalleled level of relaxation. With the elimination of futile external stimuli, the nervous system's workload is reduced by as much as 90%. Stress-related health problems such as migraine headache, hypertension, and insomnia are similarly reduced.
  • The parasympathetic system helps to increase T-cell production to strengthen the immune system.
  • This benefits the cardiovascular system by reducing blood pressure and heart rate.
  • It helps in reducing pain and fatigue. The increased endorphin levels also promote a general sense of well-being and happiness and therefore increase vitality and further reduce levels of stress and tension.
  • Due to the buoyancy effect of the salt water, all the muscles in the body relax into their natural state, relieving tension and muscle tightness.
  • The skin feels softer due to the emollient effect of the salts.
  • People with psychological and emotional problems such as anxiety and depression can also benefit from this therapy.
  • People report that they perceive less pain to stimuli after the floating tank experience.

This all happens whether an individual is awake in the tank. An hour&rsquos floating offers similar physical and mental benefits to a six-hour sleep in a bed.

Can I drown if I fall asleep in a sensory deprivation tank?

No. Some people fall asleep, but the water is so buoyant that they stay afloat. The worst that can happen is getting woken up by a bit of saltwater in the eyes. Using the shower afterward is also suggested to remove the coating of Epsom salt that is left on the skin and hair.

Each cycle can be understood as complete phases of sleep (from stage I to REM phase), and can last between 90 and 120 minutes each.

What is the dream?

When we talk about sleep or the process of sleeping, we refer to a physiological and natural state in which the level of alertness and vigilance is diminished, since the person is resting.

And although it seems that the external stillness of the subject, makes internally in a state of tranquility, it is something completely wrong, because internally the body of the sleeper does not stop and continues to function as complex as when we are awake.

The dream is composed of different degrees of intensity or depth, where in turn there are modifications of the body that accompany each phase or stage of sleep.

Basic theories about sleep

One of the first theories formulated to understand the dream process was the Passive Theory of Sleep, which Bremmer formulated in 1935. This theory was based on the fact that the excitatory areas of the brainstem were becoming exhausted throughout the day, so When it was time to sleep, they were already tired and deactivated.

It would be something similar to your mobile’s battery, taking the fact of charging it as our sleeping process.

But after several years and some experiments the theory became obsolete and a different vision began to be seen. Currently the theory that accompanies this process says that sleep is produced by an active inhibition.

This means that in the brain there is a small area that causes parts of it to be deactivated during sleep. Something like a vigilante that prevents other brain areas from doing their work while you sleep.

But you have to be clear that the brain does not sleep while you do it, but that your way of working changes to be in line with the process.

To this day, we still do not know what is the physiological purpose that creates the need of any living being to sleep. As you read above, the dream is considered a priority need, and even the fact of not sleeping for a time can cause disorders and even death although it sounds incredible.

People can not sleep without anything for 1 to 2 nights. From the third night without sleep, disorders would appear that little by little would increase in severity and would have serious consequences. This would affect areas such as attention, memory, mood and may even appear hallucinations and convulsions.

Stages of the dream

There are 4 phases of the non-REM sleep (NREM) sleep process and another of REM sleep.

NREM phase

This stage is also known as no-Rem , it comes from the English translation “non-rapid movement of the eye”, this first stage is the first contact with the dream.

It is the first state of reverie in which we enter and for most adults it will be the place that occupies 75% of the totality of your dream.

The NRem stage is divided into 4 phases , in which the characteristics of the dream are modeled , these are the following:

Stage NREM- Phase1

It is the stage where we feel drowsy or we are asleep. The waking state is disappearing since the Alpha rhythm also does it. At the moment muscle tone does not relax completely. The Beta waves have disappeared.

Stage NREM- Phase II-III

It is the stage where although we are asleep, the dream is light, the Alpha rhythm disappears more and more, muscle tone continues to exist. We experience the entrance to the theta waves little by little.

Stage NREM- Phase IV

This is the stage of deep sleep, the encephalographic rhythm is very low, muscle tone is maintained or may be greatly diminished. Delta waves appear in our brain.

Actually these stages differ in that the muscular atony is gradually increased and brain waves are gradually changing depending on the relaxation of the body.

REM phase

This is the paradoxical dream phase, since during this phase the brain has an activity that resembles that which occurs when we are awake. Also during this phase rapid eye movements are seen. The body is in atony.

What we dream of occurs during this phase.

To this day, there is no clear theory of why ocular movement occurs during the REM phase.

How is sleep organized during the night?

Adults usually have about 8 hours of sleep per day. If the 8 hours are carried out in a continuous manner, it will take about 4 or 5 cycles.

Each cycle can be understood as complete phases of sleep (from stage I to REM phase), and can last between 90 and 120 minutes each.

The distribution is usually the following:

  • Phase I during the cycle would be developing approximately 1.5% of the total cycle. This means that if the cycle lasts 100 minutes, only 1 minute and a half the body would be in phase I.
  • Phase II during the cycle would be present approximately 25% of the total cycle. In a cycle of 100 minutes, 25 minutes would be the duration of Phase II.
  • Phase III and IV during the cycle would last 45% of the total cycle. In a 100 minute cycle, these phases would last approximately 45 minutes.
  • The REM phase, during the cycle would have a duration of 25% of the total cycle. So in a cycle of 100 minutes, only 25 minutes correspond to the paradoxical dream and dreams.

How much do people sleep?

The distribution of sleep throughout the day are different according to several factors such as age, daily activity, health, etc …

Babies sleep most of the time, although as the child grows the waking states are more and more prolonged. It is curious to know that babies have a higher percentage of REM sleep than adults, and it is throughout childhood when that percentage will begin to fall to reach a normalized percentage.

In adults, the need to sleep is less than in infants. An adult can sleep between 5 and 9 hours and have a good performance throughout the day. Although it is always advised to sleep between 7 or 8 hours a day to have good health and quality of life.

Different times of life and life situations can reduce the amount of sleep. For example, when we go through times where we have a lot of intellectual activity we will have more need to sleep, than at times when stress is very present in our lives.

Older people have less need for sleep and their rest periods are less. They usually wake up during the night and the percentage of phase IV of sleep. However, the REM phase seems invariable throughout life in terms of its duration in the sleep cycle.

The dream is governed by a biological clock

The sleep process is governed by a biological rhythm understood as circadian rhythm. These are 24-hour cycles that are related to day and night.

The circadian rhythm of sleep and wakefulness is approximately every 25 hours. This data is curious because this tells us that we are programmed in such a way that we allow ourselves to be influenced by a certain rhythm or cycle.

In our central nervous system there is one of our biological clocks. This watch makes non-REM sleep and REM sleep last a certain time.

Circadian rhythms depend on the interaction of the organism with the stimuli that come from outside. Of these external stimuli the most important and the one that most influences us is light, as well as the time to wake up, since this time can be fixed strictly.

The time we go to sleep is also important, and although we can set a routine guidelines that make us at a certain time we are in bed, we can not usually decide the exact moment in which we fall asleep.

If the person is totally isolated from these stimuli, that is, he does not perceive changes of light, temperature, activities, etc … he would also follow a normal biological rhythm of sleep, since the human body is programmed to follow the rhythm we need without need for external influences.

When we dream our brain does not rest just like us, because the brain activity continues in constant and active movement.

Also while we sleep we have some curious experiences, called dreams or more commonly known as dreams.

As you read above, dreams occur during the REM phase (hence many experts think that the movement of the eyes occurs as a result of those dreams) and are in color and moving, as if we were watching a movie.

During the deep sleep phase, sometimes you also dream. The only difference is that those dreams are of a more abstract kind.

During REM sleep, the reticular system is activated in our brain, which is related to the brain and forebrain. These structures are also activated when we are awake. These structures are involved in sensory stimulation, so being activated explains why when we dream we have the feeling of actually living that dream. We can even feel what we dream.

In addition, the limbic system is active during sleep, with structures such as the amygdala and the cingulate cortex. This system is responsible for the emotional life, so this can also give a rational explanation of why during sleep we not only sensoryly sense what we are dreaming, but we also feel it emotionally.

During sleep, the prefrontal cortex, which is responsible for mental reasoning, is inhibited, so this can give us relevant information about the little logic that our dreams often have.

I hope that this article has given you information that you did not know about the natural process of sleeping that you do every night.

To finish with the article I leave here 6 curiosities about the dream that perhaps you did not know.

Freud’s Method of Dream Interpretation

“I shall bring forward proof that there is a psychological technique which makes it possible to interpret dreams, and that, if that procedure is employed, every dream reveals itself as a psychical structure which has a meaning and which can be inserted at an assignable point in the mental activities of waking life.”

– Sigmund Freud

According to Freud, all dreams can be traced to a waking element, thus it is possible to decipher and interpret dreams with scientific precision. From this stance, Freud developed a surprisingly simple method for interpreting dreams:

1. Psychological Preparation of the client: “We must aim at bringing about two changes in him: an increase in the attention he pays to his own psychical perceptions and the elimination of the criticism by which he normally sifts the thoughts that occur to him. In order that he may be able to concentrate his attention on his self-observation it is an advantage for him to lie in a restful attitude and shut his eyes.” (The Interpretation of Dreams, Pg. 126).

“We are not in general in a position to interpret another person’s dream unless he is prepared to communicate to us the unconscious thoughts that lie behind its content.” (The Interpretation of Dreams, Pg. 259).

2. Ask Specific Questions: After the client is comfortable, fully relaxed, and able to describe the dream without conscious effort, you can begin asking about certain components of the dream. It is important to ask questions regarding specific instances in the dream, rather than about the whole dream.

“If I say to a patient who is still a novice: ‘What occurs to you in connection with this dream?’ as a rule his mental horizon becomes a blank. If, however, I put the dream before him cut up into pieces, he will give me a series of associations to each piece, which might be described as the ‘background thoughts’ of that particular part of the dream.” (The Interpretation of Dreams, Pg. 126).

3. Have the Client Derive their own Meaning of Components of their Dream: With the understanding that all dream content is derived from waking phenomenon, it is possible to then identify certain dream symbols and feelings and connect them to the patient’s waking events.

In order to uncover the waking elements behind a dream, it is necessary to encourage the client to explore their thoughts freely and without shame. For example, if a client describes a weapon used in a nightmare, ask questions to uncover the root of that weapon. After doing so, it is possible to move on to the next dream experience (or item) and begin piecing together the common threads within the dream. This process will eventually lead to a broader understanding of the dream as a whole.

Supporting Information

Code S1

Matlab code for estimating instantaneous wake probability from simultaneously observed EEG, EMG, and behavioral data.

Figure S1

Data from the first (A) and second (B) consecutive experimental night for a subject with the alpha dropout phenotype. In this subject, for both nights, alpha diminishes before loss of behavioral response.

Figure S2

Data from the first (A) and second (B) consecutive experimental night for a subject with the alpha dropout phenotype. In this subject, for both nights, alpha diminishes before loss of behavioral response.

Protocol S1

Technical details on the model implementation, the particle filter algorithm, and the Bayesian goodness-of-fit procedure.