Case 4 - The Hand With a Mind of its Own

Question 1

Alien Hand Syndrome

Answer 1

A neurological disorder characterized by involuntary, purposeful actions of one hand that are perceived as foreign or controlled by an external agent.
Loss of a sense of agency, with the affected hand seeming to act independently of the individual’s will.

Question 2

Neural Correlates of AHS:

Answer 2

Associated with lesions in the medial frontal lobes (e.g., SMA/pre-SMA), corpus callosum, and sometimes seen in corticobasal degeneration.
Recent reports indicate occurrences after posterior parietal or cerebral artery strokes.

Question 3

Sense of Agency:

Answer 3

Created by minimal discrepancy between motor command prediction and sensory outcome.
Libet’s experiments suggest conscious intention follows neural signals, challenging the role of free will in volitional acts.

Question 4

Intentional Binding:

Answer 4

Measure of agency - actions perceived closer in time if followed by a tone, and tones perceived earlier if preceded by an action.
Altered awareness and control of action observed in CBS patients with AHS.

Question 5

Automatic Actions and Affordances:

Answer 5

Objects can automatically prime individuals to act, known as “object affordance.”
AHS may represent an exaggeration of affordance effects seen in healthy adults.

Question 6

Studies on AHS:

Answer 6

Sparse systematic investigations due to the rarity of the syndrome.
Experiments with CBS patients showing unwilled grasping behavior in response to simple observation of a graspable object.

Question 7

Conclusions on studies of AHS

Answer 7

AHS patients may exhibit exaggerated affordance effects, where objects automatically evoke actions.
Unlike healthy adults, individuals with AHS may act on affordances more frequently.

Question 8

Endogenous Control:

Answer 8

Involves internally-generated (endogenous) actions, distinct from externally-driven (exogenous) actions.
Medial frontal regions implicated in voluntary action control, but damage to these areas associated with Alien Hand Syndrome (AHS).

Question 9

Types of AHS Errors:

Answer 9

Patients with AHS may exhibit fluctuating behaviors, more common when fatigued or anxious.
Uncontrollable reaching, grasping, and using objects with intermittent voluntary control.

Question 10

Experiment 2 - Attentional Load:

Answer 10

Introduced a secondary task load to divert attention from the primary task.
More errors in AHS behaviors under increased attentional load, suggesting a resource-limited endogenous control system.
Conclusions:

Failures of voluntary control lead to unwilled grasping movements, evident through increased exogenously-driven errors.
Resource limitations result in more errors, implying that AHS behaviors may be regulated by a resource-limited endogenous control system

Question 11

Brain Mechanisms for Control:

Answer 11

Brain models involve top-down control, executive functions, and supervisory attention systems.
Questions arise about what initiates and directs control mechanisms.

Question 12

Unconscious Activation of Associations:

Answer 12

Voluntary control involves suppressing unwanted activation of condition-action associations.
A key aspect is preventing unwanted activation of motor responses.

Question 13

Choice and Unwanted Activation:

Answer 13

Voluntary behavior requires choice, and areas associated with ‘volition’ are involved in suppressing unwanted motor plans.
No need for a central command or homunculus; automatic suppression of unwanted motor plans occurs.

Question 14

Hypothesis for AHS:

Answer 14

AHS may result from the activation of the motor system and a deficiency in automatic inhibition.
Patients with AHS may lack the automatic suppression of actions evoked by the environment, leading to grasping behaviors.