Typically caused by damage to the subthalamic nucleus or nuclei, hemiballismus movements are nonrhythmic, rapid, nonsuppressible, and violent. They usually occur in an isolated body part, such as the proximal arm.
|
|
A tic is a sudden, repetitive, nonrhythmic motor movement or vocalization involving discrete muscle groups.American Psychiatric Association (2000). DSM- IV-TR: Tourette's Disorder. Diagnostic and Statistical Manual of Mental Disorders, 4th ed.
|
|
Tic disorders are defined in the Diagnostic and Statistical Manual of Mental Disorders (DSM) based on type (motor or phonic) and duration of tics (sudden, rapid, nonrhythmic movements).American Psychiatric Association (2000). DSM-IV- TR: Tourette's Disorder. Diagnostic and Statistical Manual of Mental Disorders, 4th ed.
|
|
Opsoclonus refers to uncontrolled, irregular, and nonrhythmic eye movement. Opsoclonus consists of rapid, involuntary, multivectorial (horizontal and vertical), unpredictable, conjugate fast eye movements without inter-saccadic intervals. It is also referred to as saccadomania or reflexive saccade. The movements of opsoclonus may have a very small amplitude, appearing as tiny deviations from primary position.
|
|
Athetosis is defined as a slow, continuous, involuntary writhing movement that prevents the individual from maintaining a stable posture. These are smooth, nonrhythmic movements that appear random and are not composed of any recognizable sub- movements. They mainly involve the distal extremities, but can also involve the face, neck, and trunk. Athetosis can occur in the resting state, as well as in conjunction with chorea and dystonia.
|
|
Chorea gravidarum is a rare type of chorea which presents with involuntary abnormal movement, characterized by abrupt, brief, nonrhythmic, nonrepetitive movement of any limb, often associated with nonpatterned facial grimaces. It is a complication of pregnancy which can be associated with eclampsia and its effects upon the basal ganglia. It is not a causal or pathologically distinct entity but a generic term for chorea of any cause starting during pregnancy. It is associated with history of Sydenham's chorea.
|
|
Myoclonus is defined as a sequence of repeated, often nonrhythmic, brief, shock-like jerks due to sudden involuntary contraction or relaxation of one or more muscles. These movements may be asynchronous, in which several muscles contract variably in time, synchronous, in which muscles contract simultaneously, or spreading, in which several muscles contract sequentially. It is characterized by a sudden, unidirectional movement due to muscle contraction, followed by a relaxation period in which the muscle is no longer contracted. However, when this relaxation phase is decreased, as when muscle contractions become faster, a myoclonic tremor results.
|
|
Tourette syndrome is classified as a motor disorder (a disorder of the nervous system that causes abnormal and involuntary movements). It is listed in the neurodevelopmental disorder category of the fifth version of the Diagnostic and Statistical Manual of Mental Disorders (DSM-5), published in 2013. Tourette's is at the more severe end of the spectrum of tic disorders; its diagnosis requires multiple motor tics and at least one vocal tic to be present for more than a year. Tics are sudden, repetitive, nonrhythmic movements that involve discrete muscle groups, while vocal (phonic) tics involve laryngeal, pharyngeal, oral, nasal or respiratory muscles to produce sounds.
|
|
Tics may increase when someone is experiencing stress, fatigue, anxiety, or illness, or when engaged in relaxing activities like watching TV. They sometimes decrease when an individual is engrossed in or focused on an activity like playing a musical instrument. In contrast to the abnormal movements associated with other movement disorders such as choreas, dystonias, myoclonus, and dyskinesias, the tics of Tourette's are nonrhythmic, temporarily suppressible, and often preceded by an unwanted urge. The ability to suppress tics varies among individuals, and may be more developed in adults than children. People with tics are sometimes able to suppress them for limited periods of time, but doing so often results in tension or mental exhaustion.
|
|
Each part of the brain shows a mixture of rhythmic and nonrhythmic activity, which may vary according to behavioral state. In mammals, the cerebral cortex tends to show large slow delta waves during sleep, faster alpha waves when the animal is awake but inattentive, and chaotic-looking irregular activity when the animal is actively engaged in a task, called beta and gamma waves. During an epileptic seizure, the brain's inhibitory control mechanisms fail to function and electrical activity rises to pathological levels, producing EEG traces that show large wave and spike patterns not seen in a healthy brain. Relating these population-level patterns to the computational functions of individual neurons is a major focus of current research in neurophysiology.
|
|