Chapter 10 Flashcards
Action
Action is the outcome of a number of cognitive processes that translate the goals and intentions of an individual into a motor output.
Movement
Movement is a physical act that is not necessarily cognitive (e.g. reflexes).
Why is action computationally difficult
- Degrees of freedom problem: potentially infinite number of motor solutions for, say, picking up an object.
- Generalized motor programs are stored routines of actions and action sequences that minimize the problem.
- Sensory-motor transformation: linking together the position of an object in retinal space with the position of the limbs in bodily space (proprioception).
Action involves most of the brain
Frontal lobes: planning actions, maintaining goals, executing actions.
Parieto-frontal circuits: link action with current environment.
Parietal lobes: locating objects in space sensory-motor transformation.
Temporal lobes: object recognition, object knowledge.
Occipital lobes: visual analysis of scene.
Subcortex e.g. basal ganglia: modulate force and likelihood of action.
Subcortex e.g. cerebellum.
Role of frontal lobes in action - primary motor cortex
- Executes all voluntary movements of the body.
- Somatotopically organized and crossed (left hemisphere = right side of body).
- Stimulation results in movement and lesion results in paralysis (e.g. hemiplegia).
Hemiplegia: Damage to one side of the primary motor cortex results in a failure to voluntarily move the other side of the body.
Role of frontral lobes in action -frontal eye field (FEF)
Voluntary movement of the eyes. Lateral and medial premotor cortex:
- Lateral premotor cortex: prepares movement based on external contingencies, receives visual signals via parietal cortex.
- Supplementary motor area (SMA): deals with spontaneous well-learned actions that don’t place strong demands on the environment, receives strong proprioceptive signals concerning position of the limbs.
TMS in SMA = disruption of complex (prelearned) condition only.
TMS in M1 = disruption of complex & scale condition.
TMS in lateral prefrontal = no effects.
Role of frontal lobes in action - prefrontal cortex
- Involved in coordination of cognition generally (both external actions and internal thoughts).
- Involved in selection and maintenance of goals and responses.
- Involved in coordination of cognition generally.
- Involved in selection/maintenance of goals/responses.
- Damage to this region does not impair physical movement but actions become inappropriate or disorganized.
* Perseveration = repeating an action that
has already been performed and is no longer relevant
*Utilization behavior = impulsive actions on irrelevant objects in the environment
Role of the frontal lobes in action - controlled vs. automated behaviour
- Some actions can be performed in “autopilot” mode, with minimal attention to action and online control.
- Other actions require an interruption of ongoing behavior and setting up novel actions/cognitive procedures.
➡ Norman and Shallice (1986) argue that the latter, but not the former, requires the intervention of an executive called the “supervisory attentional system” (SAS).
Contention scheduling:
Selecting one schema from a host of competing schemas.
Role of frontal lobes in action - comprehension and imitation - mirror neurons
- Mirror neurons – respond to observed as well as self-enacted actions.
- Basis of learning via imitation, and possibly understanding actions of others?
Role of parietal lobes in action
- Object based action : from where to how pathway.
- Double dissociation: visual agnosia versus optic ataxia
- Patient DF visual form agnosia (cf. seeing brain).
- Optic Ataxia = Inability to use vision to accurately guide action, without basic deficits in visual discrimination or voluntary movement per se.
- With more complex objects, DF appears to use single orientations to guide actions.
- Left & right parietal lobe, often affecting the opposite hand.
- Tool use: humans have developed a huge variety of tools that are associated with specific actions and functions. Possible because of: walking upright and change in hand anatomy.
- Patients with associative agnosia are unable to recognize or comprehend familiar objects, but use of tools is ok.
- The dorsal route may compute affordances between the structure of objects and potential functions (e.g. sharp = cutting, hollow = container).
- Rumiati et al. (2004) compared the brain activity when subjects were asked to
generate actions or name actions from either an object or action. They found a
region in the left inferior parietal lobe that appears specific to object-based action in their “pantomime” condition. - Tool use in ideomotor apraxia: inability to produce appropriate gestures given an object/word/command.
- Pantomime versus meaningful actions.
Role of the subcortex in action
Two different subcortical loops: cerebellar loop and BG motor circuit:
- Cerebellar loop involved in coordination of movement, may update the motor program online using visual feedback; timing & trajectory. Patients with cerebellar lesions have tremulous movements; problems with motor learning, fine motor control, posture.
- Basal ganglia loop (actually 5+ different loops with similar architecture) important for initiation and execution of internally generated movements and linking one action to the next. Modifies the activity in frontal motor structures to influence the probability of a movement (damage leads to hypokinetic and hyperkinetic disorders).
Role of the subcortex in action - disorders
- Case without cerebellum (congenital: only mild motor problems).
- Basal ganglia disorder: Parkinson’s disease (hypokinetic). SN neurons are dopaminergic;
example of micrographia that disappears with dopaminergic agonist (e.g. Levodopa). - Basal ganglia disorder: Huntington’s disease.
- Basal ganglia disorder: Tourette’s syndrome.
Parkinson motor symptoms
- Akinesia (lack of spontaneous movement).
- Bradykinseia (slowness of movement).
- Decay of movement sequences (walking degenerates to a shuffle).
- Failure to scale muscle activity to movement amplitude.
- Failure to weld several movement components into a single action plan.
- Rigidity.
- Tremor (when stationary).
Deep brain stimulation for Parkinson disease
- Implantation of stimulating electrode & pacemaker.
- Locations within basal ganglia:
* Subthalamic nucleus
* Globus pallidus
Huntington’s disease motor symptoms
- Excessive movement, dance-like flailing limbs (chorea) and contorted postures.
- Genetic disorder (degenerative).
- Depletion of inhibitory neurons in indirect pathway (brake affected).
