TASK 2: THE SLEEPWALKING KILLER
LEARNING GOALS:
1. What are the different sleep disorders and their link to aggression?
Popat & Winslade (2015) – While You Were Sleepwalking: Science and Neurobiology of Sleep
Disorders & the Enigma of Legal Responsibility of Violence During Parasomnia
Provides a general overview of the current scientific knowledge of parasomnias.
The idea that a person can execute a coordinated act of violence in their sleep opposes the
stereotypical perception that sleepwalkers are in a mindless daze, performing actions over which
they have no control or awareness. In this manner, they present a troublesome enigma.
The stages of sleep
To categorize the different stages of sleep, 3 standard laboratory measures are used:
- Electroencephalogram (EEG): records brain activity in the form of waves
- Electrooculogram (EOG): notes eye movements
- Electromyogram (EMG): measures muscle activity via a sensor places on the chin, or
alternatively on the arm or leg
Sleep is divided into 2 parts:
- Non-rapid eye movement (NREM) sleep
o When you 1st fall asleep, you usually enter NREM sleep
o NREM sleep is divided into 4 stages:
1st stage: Thoughts start to drift, ability to react to external stimuli begins to
decrease, muscle activity begins to slow
Stage 3 & 4: The ‘deep’ stages of sleep
Waking someone during these stages of sleep often is quite difficult,
and the person awakens feeling groggy & disoriented
o As you move through the stages of NREM sleep, EEG waves grow in amplitude &
decrease in frequency – they become bigger and slower
- Rapid eye movement (REM) sleep
o After the 4 stages of NREM sleep, you move into REM sleep, where dream mentation
occurs and manifests as some cerebral activity on the EEG
o During this stage, the EOG shows rapid eye movements in random directions, and the
EMG indicates a complete lack of muscle tone
This muscle atonia prevents the individual from acting out their dreams
o Waking someone up during their REM sleep is usually effortless, and the person
wakes up with little disorientation
Each complete sleep cycle (with both NREM & REM sleep) lasts ~90 minutes in adults.
- As the night progresses, the time spent in stages 3 & 4 of NREM sleep decreases, while the
time spent in REM sleep increases
- REM sleep increases as you grow older
Clinical aspects of sleep disorders
Sleep disorders are generally divided into 2 major categories:
- Dyssomnias: the sleep disorders that manifests as “excessive sleepiness or difficulty in
initiating or maintaining sleep”
o Includes insomnia, narcolepsy, and circadian rhythm disorders (e.g. jet lag and shift
work disorder)
, o Rarely become violent in a manner in which they could be mistaken for awake &
aware actions
- Parasomnias: the sleep disorders that result in physical actions that are completely
uncharacteristic of sleep
o Many parasomnias are beyond the scope of this discussion as they, like dyssomnias,
rarely manifest with violence
o Two disorders are of particular interest in this discussion :
Somnambulism
REM sleep behaviour disorder (RBD)
Somnambulism (sleepwalking)
- Appears as episodes of motor activity ranging from walking to driving and even violence
among a variety of other inappropriate (for sleep) actions
o Significant motor activity (an aspect of wakefulness) remains during sleepwalking
- Occurs during the deepest stages of NREM sleep, stages 3 & 4
o Therefore, somnambulism is more likely to occur in the earlier part of the night when
these stages predominate
o Episodes typically last from a few minutes to an hour
May occur from once a month to multiple nights per week
o Attempts to wake individuals usually remain fruitless & sometimes even elicit violent
responses, such as aggressive and spastic limb movements
o During the episode, the individual appears awake but is unresponsive
Sensory perceptions are virtually switched off, so while the person can often
navigate around objects due to habit and simple stumbling, one does not
fully perceive any sight, smell, sound, or even pain
Eyes are usually directed upward & inward, resulting in a vacant expression
o Memories of the incident don’t carry into the waking state
If awakened during a sleepwalking episode, one usually remains confused &
disoriented for a period of time
- More prevalent in males between 7-15 years of age
o Somnambulism that results in violence usually occurs in a slightly older age group
- State dissociation theory: somnambulism is an amalgam of NREM sleep & wakefulness
REM sleep behaviour disorder (RBD)
- Occurs during the REM stage of sleep. In RBD, the muscle atonia of REM sleep is disabled
intermittently; absence of muscle atonia
o This results in a variety of behaviours that can range from talking or screaming to
thrashing one’s limbs about in bed and even more seemingly coordinated violence
Individuals with RBD tend to awaken as their feet hit the floor or soon after,
so violent actions usually target the bed partner or those nearby
o RBD usually occurs in the later parts of sleep in the early morning, when more time is
spent in REM sleep
- Because RBD is essentially acting out one’s dreams, one will remember bits and pieces of the
events from the episode in the form of a vivid but disconnected dream
o Since one can awaken more easily from the lighter REM sleep, one with RBD will not
appear as disoriented afterwards
Neurobiology of parasomnias and correlates with legal responsibility
Alpha motor neurons control skeletal muscle fibres, which are responsible for the majority of body
movements. During sleep, the input signals to these neurons change.
- Excitatory impulses, which depolarize these neurons, decrease
, - Inhibitory signals, which hyperpolarize the alpha motor neurons, increase
o To reach the threshold potential in a hyperpolarized cell requires a significantly
greater net depolarization, i.e. a much larger excitatory impulse
=> Transmitting an action potential to skeletal muscle is much less likely
- During REM sleep, the alpha motor neuron membrane are significantly more hyperpolarized,
making it even more difficult for impulses to fire and cause movement
Examination of the brains of sleepwalkers: Cerebellum & brainstem are active, while the cerebrum &
cerebral cortex show little activity
- Brainstem & cerebellum: contribute to the activity of motor neurons, involved in extremely
complex emotional and motor behaviours without involvement of ‘higher’ neural structures
- Cerebrum & cerebral cortex: control & regulate actions, rather than initiate them
o Coordination & integration of info between parts of the cerebral cortex is an
important precursor for consciousness
Therefore, while asleep, one essentially acts without any consciousness
o Parts of the cerebrum contribute to sensory processing & formation of new
memories
Therefore, one does not remember episodes of parasomnia
Absence of consciousness during parasomnias can be verified from more indirect evidence as well
- Sensory perception, voluntary control of motor activity, and the ability to interact with &
experience the world are considered as important aspects of consciousness
o During episodes of parasomnia, one does not have any sensory perception, memory
formation, or responsiveness toward the environment – they have absolutely no
mental interaction with the outside world
In other words, they’re completely unaware during an episode of
parasomnia: individuals in parasomnia episodes are neither awake nor aware
- The inability to form conscious intentions is a prominent characteristic of parasomnias that
has significant legal ramifications
Actus Reus and Mens Rea: Freedom from responsibility in legal theory
Common law legal systems discuss two components to every crime:
- Actus reus: the criminal act itself
- Mens rea: the criminal intent
o In the case of parasomnias, mens rea is absent. The individual is neither awake,
aware, nor able to make a decision to not act
o Automatism: a condition in which activity is carried out without conscious
knowledge on the part of the subject
Parasomnias are clearly automatisms
Automatisms usually lead to legal acquittal due to the lack of mens rea
Automatisms are commonly divided into two categories :
Sane automatisms
o Result from an external factor, such as a blow to the head
o Result in complete acquittal
Insane automatisms
o Due to some sort of internal factor like a brain tumour or a
psychological disorder, referred to as “diseases of the mind”
o Traditionally result in compulsory confinement in a
psychiatric facility
- If one of these components is absent, the defendant is acquitted
