MCAT Content / Consciousness / States Of Consciousness

States of consciousness

Topic: Consciousness

Consciousness describes our awareness of internal and external stimuli. Awareness of internal stimuli includes feeling pain, hunger, thirst, sleepiness, and being aware of our thoughts and emotions. Consciousness can be viewed as a continuum that ranges from full awareness to deep sleep.

Alertness and Sleep

Wakefulness is characterized by high levels of sensory awareness, thought, and behavior. In between these extremes are states of consciousness related to daydreaming, intoxication as a result of alcohol or other drug use, meditative states, hypnotic states, and altered states of consciousness following sleep deprivation. We might also experience unconscious states of being via drug-induced anesthesia for medical purposes.

Biological rhythms govern states of consciousness. Changes in body temperature and alertness that fluctuate cyclically over a 24-hour period are examples of a circadian rhythm. A circadian rhythm is a biological rhythm that takes place over a period of about 24 hours. Alertness is associated with higher body temperatures and sleepiness with lower body temperatures. 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. 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

The other end of the continuum from alertness is sleep. Sleep is a state marked by relatively low levels of physical activity and reduced sensory awareness that is distinct from periods of rest that occur during wakefulness.

Sleep cycles and stages

The overall sleep cycle is comprised of two broad alternating cycles, REM (rapid eye movement), and NREM (non-rapid eye movement), which consists of three individual phases—N1, N2, and N3.

Stage 1 NREM is characterized by lowered brain activity, blood pressure, and muscle tone.

Stage 2 NREM is characterized by muscular activity decreasing, and conscious awareness of the external environment disappears.

Stage 3 NREM is deep sleep that occurs 30–45 minutes after falling asleep, and many environmental stimuli no longer produce any reactions. It is characterized by regular breathing and regular, slow brain waves.

REM sleep is the deepest sleep stage and is characterized by partial paralysis, vivid dreaming, and an EEG that resembles waking brain activity.

Sleep has four distinct phases or stages. Sleep progresses from stage 1 to stage 2 to stage 3, and then back to stage 2 before transitioning into the REM phase. Once the REM phase is over, stage 2 will repeat. A person will complete this entire cycle about four or five times given a full night of sleep. A sleeper first enters REM sleep after about an hour and a half of sleep, and then the phase will last only briefly. However, for each successive sleep cycle, the proportion of the cycle spent in REM sleep increases, up to an hour-long in later cycles.

Sleep deprivation and disorders

Sleep deprivation tends to cause slower brain waves in the frontal cortex, shortened attention span, higher anxiety, impaired memory, and an unhappy mood. Conversely, a well-rested organism tends to have improved memory and mood. Research has demonstrated that some sleep stages are more important than others in achieving restfulness. For example, REM deprivation causes a significant increase in the number of attempts to go into the REM stage while asleep. A phenomenon called REM rebound refers to the increase in frequency and depth of REM stage sleep after sleep deprivation.

Sleep-wake disorders cause a number of sleep disturbances that affect the amount, quality, or timing of sleep or that induce abnormal events during sleep. Some sleep-wake disorders are serious enough to interfere with normal physical, mental, and emotional functioning.

Insomnia refers to a chronic difficulty in falling asleep and/or maintaining sleep when no other cause is found for these symptoms. It is often a symptom of a mood disorder (e.g., emotional stress, anxiety, depression), an underlying health condition (e.g., asthma, diabetes, heart disease, pregnancy, or a neurological condition), or abuse of alcohol or drugs

Hypersomnolence disorder (also known as idiopathic hypersomnia) is a disease of likely neurological origin that is characterized primarily by severe, excessive daytime sleepiness. It has been diagnosed only rarely and is often very difficult to diagnose at an early stage. It is usually a debilitating lifelong disease.

Narcolepsy is also referred to as excessive daytime sleepiness (EDS). Individuals with this disorder often fall asleep spontaneously but unwillingly at inappropriate times. People with narcolepsy tend to have trouble in areas such as work, leisure, and personal relationships.

Parasomnias are a category of sleep disorders that involve abnormal movements, behaviors, emotions, perceptions, and dreams that occur while falling asleep, while sleeping, while between sleep stages, or during arousal from sleep. Some examples of these are sleepwalking, sleep terrors and restless leg syndrome.

Some sleep disorders are caused by disturbances in breathing. Sleep apnea, for example, is a disorder in which obstruction of the airway during sleep causes a lack of sufficient deep sleep, often accompanied by snoring. Sleep apnea is usually caused by some sort of physical condition that obstructs the breathing system, such as obesity, rather than a mental condition.


Sigmund Freud and Carl Jung put forth some of the best-known modern theories of dreaming; Freud believed that dreaming allows us to sort through unresolved, repressed wishes, while Jung believed that dreams present the dreamer with revelations to resolve emotional or religious problems and fears.

Freud’s theory describes dreams as having both latent and manifest content; latent content relates to deep unconscious wishes or fantasies, while manifest content is superficial and meaningless.

Other theories on dreams have been proposed to explain dreaming whilst in REM sleep:

Threat-simulation theory suggests that dreaming should be seen as an ancient biological defense mechanism that provides an evolutionary advantage because of its capacity to repeatedly simulate potential threatening events, thus enhancing the mechanisms required for efficient threat avoidance.

Activation-synthesis theory states that dreams don’t actually mean anything. Instead, dreams are merely electrical brain impulses that pull random thoughts and imagery from our memories. The theory posits that humans construct dream stories after they wake up, in an attempt to make sense of it all.

The continual-activation theory proposes that dreaming is a result of brain activation and synthesis; its assumption is that, during REM sleep, the unconscious part of the brain is busy processing procedural memory.

Hypnosis and Meditation

Hypnosis is a trance-like state in which a person experiences heightened suggestibility Hypnosis can be used for many things, including pain management, addiction management, and weight loss this is because when a person is in an altered state of perception under hypnosis, it is thought that they can be guided to experience a reduction in pain, change ineffective cognitions or beliefs, or remember forgotten memories.

Meditation is the practice of training the mind in order to induce relaxation or an altered mode of consciousness. Meditation has a variety of health benefits, including lowered stress levels, increased immune system function, and decreased muscle tension. Techniques for meditation vary between cultures. Breathing meditation involves focusing on the breath entering and leaving the body. Devotional meditation involves focusing on a particular object or concept. Relaxation meditation involves tensing and relaxing different muscle groups to achieve relaxation of the mind and the entire body

Practice Questions

Khan Academy


MCAT Official Prep (AAMC)

Online Flashcards Psychology Question 10

Section Bank P/S Section Passage 7 Question 54

Practice Exam 3 P/S Section Question 13

Key Points

• Consciousness can be treated on a continuum between sleep and alertness (wakefulness) with different characteristics in psychological and biological behavior determined by circadian rhythms.

• Sleep has 4 main stages and is important for the recovery and growth of the body. REM is the deepest form of sleep and shows similar brain patterns to alert brain patterns. When an organism sleeps the length of sleep required is determined by age and activity.

• Sleep cycles are cycles of the 4 stages of sleep over a chronological period

• Several theories attribute dreaming as an important mental process, processing and making light of information and stimuli received in the day

• Sleep deprivation and sleep-wake disorders can disturb sleep and causes mental and physical problems

• Altered states of consciousness can be bought about through meditation and hypnosis. Changing a person’s perception or conscious state.

Key Terms

REM sleep: the stage of sleep during which most brain activity and dreams occur, characterized by rapid eye movement (REM)

Manifest: obvious to the understanding; apparent to the mind; easily apprehensible; plain; not obscure or hidden

Latent: existing or present but concealed or inactive

Hypnosis: an artificially induced trancelike state in which a person has heightened suggestibility and may experience suppressed memories

Consciousness: the state of being aware; awareness of both internal and external stimuli

Meditation: a practice in which an individual trains the mind and/or induces a mode of consciousness to realize some benefit; a devotional exercise of, or leading to, contemplation

Circadian rhythm: a biological rhythm that takes place over a period of about 24 hours

Melatonin: a hormone that regulates the sleep–wake cycle

Pineal gland: a gland inside the brain that releases melatonin

Sleep deprivation: the condition of not having enough sleep

REM rebound: the increase in frequency and depth of REM stage sleep after sleep deprivation.

Insomnia: refers to a chronic difficulty in falling asleep and/or maintaining sleep

Narcolepsy: a sleep awake disorder, sufferers often fall asleep spontaneously but unwillingly at inappropriate times

Parasomnias: a category of sleep disorders that involve abnormal movements and behaviors

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