Introduction:

Alien Hand Syndrome (AHS) is a motor disorder characterized by a unilateral limb performing a purposeful, involuntary movement. AHS is a rare disorder but has been in existence for centuries. It was given it's official name in 1972 [5]. While it is difficult to localize the cause of this disease, it has been throughly researched and many theories and probable causes are offered. AHS has been categorized into three variants: frontal, callosal and sensory [3]. Frontal and callosal variants are grouped together as anterior variants while the sensory is considered a posterior variant. Each of these variants are associated with specific characteristics, but general characteristics associated with AHS are apraxia, impairments to speech and odd movements that can be misinterpreted as intentional movements [5]. The cause of AHS for an individual is localized through evaluating the displayed symptoms. This can prove challenging as multiple variants may be present in one individual. The anterior and posterior variants of AHS are each associated with specific locations and causes of the disorder. Each case of AHS is unique, proving it difficult to pin point a single, universal cause and therefore, treatments. Many potential options are offered, but none are publicly approved.


Functional Anatomy:


motor areas.jpg
[1*]


  • Supplementary Motor Cortex: Anterior to the primary motor cortex; superior to Premotor Cortex; a portion of the cerebral cortex
    • plans movement in advance
    • used in self initiated, complex movements
  • Premotor Areas: Directly inferior to Supplementary motor cortex and directly posterior to prefrontal cortex; receives information from the prefrontal areas; part of Brodmann's Area 6
    • assists in complex, coordinated movement
    • chooses a motor program to accomplish the goal
  • Prefrontal Cortex: the most anterior portion of the brain; part of the cortex of the frontal lobe.
    • identifies the intention for movement
    • makes the decision that movement is needed
    • spatial orientation


278235676.jpg
[2*]

  • Cingulate Gyrus: the fold of the brain superior to the corpus callosum. Part of the limbic system, which is related to emotions and memory.
    • regulates emotional responses (i.e. aggressive, anxious behavior)
    • compulsive goal specific behaviors

713596777.PNG
[2*]

  • Corpus Callosum: white matter; neuronal axons that connect the right and left hemispheres of the brain
    • allows for decussation of information in higher processing systems


Potential Causes: [2,5]
  • any disconnect or disruption of neuronal pathways
  • anterior cerebral artery stokes
  • midline tumors
  • seizures
  • migrane aura
  • autoimmune disorders with hemiatrohpy
  • lesions in higher processing loops and circuitry


AHS: the three Variants

AHS occurs when there is a wedge between consciousness and the feeling of free will. Individuals with AHS tend to experience negative emotions toward the affected hand due to lack of control over the limb. [4]

  • Anterior Variants
    • Frontal:
      • Structures: Supplementary Motor Area, Cingulate cortex, Prefrontal cortex
      • Characteristics: groping, grasping, compulsive use of objects nearby, unable to command limb to move, increased tone in limb, inappropriate behavior (i.e. choking, sexual), negative emotion towards hand [1,3,4,5]
      • Discussion: These characteristics are actions intended to be the result of a goal-oriented motor behavior [5]. When a lesion or damage to any of the structures above occurs, there is a chance that these characteristics may become prominent and result in involuntary motor commands being performed. The Supplementary Motor Area (SMA) and medial Premotor Area are associated with self-initiated, complex movements that are planned in advance. When injury occurs in these areas, complex actions such as grasping and manipulation of objects are not inhibited in the planning and processing loops, therefore executed by the motor cortex. An injured Prefrontal cortex is unable to communicate to the premotor areas that a movement is not needed allowing for inappropriate motor actions. Or, in the case of an inability to command limb movements, that a behavior is needed.The characteristic of groping is associated with lesions to the contralateral medial frontal cortex and SMA [3]. When the cingulate gyrus is damaged, there is a lack of communication in the network syste
        alien-hand-1-1.jpg
        [3*]
        m to influence the force and magnitude of a grasping motor command. This area is also responsible for the emotional detachment and belief that the limb does not belong to the individual (foreignness). [5] Damage to these areas leads to a decrease in the planning and selection of which motor program to run. This lack of inhibition of movements leads to the groping, grasping, operation of objects and inappropriate behavior. It is common for people that exhibit these characteristics to have anxiety when in public. While it is appropriate to not want to have AHS act up in public, anxiety and worry aggravates and increases the behavior [3].
    • Callosal:
      • Structures: Corpus Collosum
      • Characteristics: intermanual conflict, diagnostic dyspraxia; interfering actions [1,3,5]
      • Discussion: This variant is typically initiated by external stimuli rather than goal oriented behavior as frontal variant cases. Self oppositional behavior is traced directly to damage of the Corpus Callosum.[3] These characteristics become prominent because there damage to axons that share information between the two sides of the brain. The right hemisphere controls the left side of the body while the left hemisphere of the brain controls the right side of the body. This disorder typically affects only one half of the brain, so only one limb. The limb functioning normally is capable to carry out motor programs, but since there is little control and processing on the damaged side, unprocessed programs are executed. These programs with the callosal variant typically fight with voluntary hand. This consists of the affected hand undoing the finished voluntary movement. The movements that contradict may be reflex movements that are carried out since there is no higher processing inhibiting the movement. Patients with this variant also exhibit frustration due to inability to accomplish goals from inter manual conflict. [5] To have coordination of the hands together requires bilateral hemisphere activation and communication.

  • Posterior Variants
    • Sensory Alien Hand
      • Structures: Parietal Cortex
      • Characteristics: lack of proprioception, foreignness, ataxic movements, inability to perform specific tasks, excessive attention to unimportant tasks [1,3,5]
      • Discussion: Feelings of unawareness of spatial location and that the hand does not belong to oneself are characteristics traced to the posterior parietal cortex. [3] Both of these sensations may be due to interrupted sensory feedback [1] Patients with the posterior variant are aware that that the limb is in motion but there is a lesion causing a disconnect between the intended action and results: feedforward and feedback. Since the movement was not intended by the individual and the feedback is unable to get processed properly, the movement is considered involuntary and foreign. [1] When there is a disruption to the flow of information, it will interfere with processing and interpretation of proprioception. This flow of information taps into the dorsal stream pathway which is processing where an object is (image below). This pathway gathers the proprioceptive as well as visual sensory input. A lesion in the posterior partial region would disrupt this dorsal stream processing system which travels through the parietal cortex, therefore, the patient would have a lack of spatial awareness.[2] There is also newer research showing that damage to the loops between the cortex, basal ganglia and thalamus may contributed to posterior symptoms as well. [3]

00465.jpg
[4*]


Dorsal Steam ("Where") Pathway:
The sensory information is brought in through their individual pathways via nerves to the brain. This information gathers for initial processing in V1, which identifies speed, direction, spatial frequency, temporal frequency, orientation and color of objects in the visual field. The information pertaining to speed, direction, spatial frequency and temporal frequency proceed to the region V2. From here it goes to the MT where directional mapping begins to get processed: whether the object is near or far from the individual. Next the information travels to the MST where expansion, contraction, rotation and optic flow are processed. The last step of the dorsal, pathway is to the parietal regions. The parietal regions continue to process the optic flow of spatial location, self motion and multimodal integration (the integration of information from all over the brain-- somatasensory and visual specifically).


Example of AHS:
jnnp-2008-March-79-3-246-F3.large.jpg
[5*]

Top Left: voluntary reach for object. Top Right: voluntary movement of left hand and beginning of affected hand going for the object. Bottom Left: affected hand moves object involuntarily (intermanual conflict) Botton Right: Subject grabs and restrains alien hand

Potential Treatments [5]
  • Botulinum Toxin: weakens arm muscles; alters sensory feedback between brain and arm
  • Spatial recognition exercises
  • Verbal cues
  • Visual reinforcement (Specifically for Posterior variant AHS)
  • Sensory Tricks (cover affected hand)
  • Behavioral modifications

Each of these treatments above have been attempted, but none have been proven to have long term effects. Since each case of AHS is individualized, the treatments will need to be individualized also. A typical response of someone affected by this movement disorder is to sit on the hand in order to suppress unwanted movements.This is in attempts to minimize the visibility of the disorder, but in no way treats the disorder. Other short term approaches may be to refrain the patient from multitasking or try to keep their surrounding environment relatively simple and distraction free [5]. Research is leading to the belief that callosal variants seem to be the most susceptible to treatment.

Conclusion

All body parts are capable and functioning, but the limbs may not be in communication with higher processing systems, allowing for unwanted movement to be performed. The three types of Alien Hand Syndrome are frontal, callosal and posterior. Each have distinguished characteristics. These characteristics are a result of damage to different areas of the brain: supplementary motor area, prefrontal cortex, premotor areas, cingulate gyrus, corpus collasum, parietal lobe or any lesion to the processing network within the brain. This is a rare syndrome and has proved unique in every case seen. Because of this, it is challenging to perform studies to determine exact, traceable causes and locations for AHS. The parietal lobes (posterior variant) provide primitive aspects of motor movements and the frontal variants process information into goal specific movement, and when these areas are damaged characteristics pertaining to these functions will result [1]. Steps required to experience AHS: disinhibition of limb, a purposeful movement occurs, and an awareness that the movement was not consciously desired [1].


Glossary
  • agnosia: inability to interpret sensations or recognize things.
  • agnostic dyspraxia: when one hand does not respond to a motor control and the contralateral hand compulsively performs the desired movement [3]
  • apraxia: when someone is willing to perform a movement but is physically incapable to plan and execute the desire motion.
  • ataxia: abnormal, involuntary movements
  • groping: unintended reaching out; searching with the hands [3]
  • hemiatrophy: when one side of the body (aspect of the body) grows more developed than the contralateral
  • intermanual conflict: the affected hand counteracts the voluntary actions of the voluntary hand (self-opposition)
  • involuntary: lacking conscious control; done without or against an individual's will
  • varient: a form or version of something that differs in some respect from other forms

Relevant Links and Suggested Reading

This video provides a look into experiments with patients with AHS as well as brief commentary and explanation from the man who coined the term "Alien Hand" in English.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4059570/pdf/bumc0027-0219.pdf
This link is to a short case study and brief description of a women with Alien Hand Syndrome, written by four MDs.


Quiz
T/F:
1. Damage to the left hemisphere of the brain will result in AHS in the left hand.

2. All variants can be traced back to an inability to inhibit movements or a loss of inhibitory tone.

3. Anxiety of involuntary movements is a characteristic of this motor disorder.

4. AHS only affects motor control.

Multiple Choice:
5. Which is not a variant of Alien Hand Syndrome?
a. Anterior
b.Posterior
c.Frontal
d.Parietal
e.Callosal

Short Answer:
6.. What variant of AHS is displayed in the example image above?

7. What areas of the brain play a part in motor planning in advance?

Essay:
8. How does the dorsal stream relate to Alien Hand Syndrome?


Picture URLs:
[1*] http://rasmussenanders.blogspot.com/2007/02/true-cyborgs-now-reality.html
[2*] https://humanbiologybrain.weebly.com/cingulate-gyrus.html
[3*] https://science.howstuffworks.com/life/inside-the-mind/human-brain/alien-hand.htm
[4*] https://neupsykey.com/the-organization-of-cognition/
[5*] http://jnnp.bmj.com/content/79/3/246

References
[1] Biran I., Giovannetti T., Buxbaum L., & Chatterjee A. (2006). The Alien Hand Syndrome: What makes the alien hand alien? Cognitive Neuropsychology, 23(4), 563-582.

[2] Lunardelli A., Sartori A., Mengotti P., Rumiati R., & Pesavento V. (2014). Intermittent Alien Hand Syndrome and Callosal Apraxia in Multiple Sclerosis: Implications for Interhemispheric Communication. Retrieved December 03,2017 from https://hindawi.com/journals/bn/2014/873541/.

[3] Mark V.W. (2007). Alien Hand Syndrome (S. Gilman, Ed.). MedLink Neurology. Retrieved December 03,2017 from https://www.jsmf.org/meetings.

[4] Persaud R. (1999). Sensory Alien Hand Syndrome. Retrieved December 03,2017 from http://jnnp.bmj.com/content/67/1/130

[5] Sarva H., Deik A., &Severt W. L. (2014). Pathophysiology and Treatment of Alien Hand Syndrome.Retrieved December 03,2017 from https://www.ncbi.nih.gov/pmc/articles/PMC4261226

Quiz Answers:
1.F 2.T 3.T 4.F 5.D 6.Intermanual conflict characterizes the Callosal variant. 7. Supplementary cortex area, premotor and prefrontal.
Essay: 8. The dorsal stream is involved specifically with the posterior variant of Alien Hand Syndrome because both involve the parietal lobe. When the parietal lobe is damaged AHS symptoms such as unawareness of where there limb is in space or what it is doing. Their sensory information taken in with the affected hand will also not be able to be processed properly. This sensory information gets processed through the dorsal stream in order for the brain to select a response motor command. The dorsal stream's input from the premotor and motor areas will be affected (not enough information will be processed) and it will lead to the selection of improper motor programs. Since there is disconnections in the neurological network, the individual may be unaware that a motor program is passed through these pathways and is executed in the limb involuntarily. The disruption of the dorsal pathway is why someone with posterior variant AHS thinks of their hand as a foreign being and they are unaware of its location and actions.