Action

1. Action What is apraxia? Types of apraxia Cognitive models Disconnection syndromes The alien hand Summary

2. Parietal lobe and vision

3. The parietal lobes • The parietal lobes have two main functions: • The first function integrates sensory information from vision, audition and somatosensory input to form a single perception that can be ‘recognised’. • The other function constructs a spatial system to represent the environment around us (peri-personal space) and is used to guide actions.

4. Two visual systems • The ventral or ‘what’ stream runs from the striate cortex into the temporal lobe and is involved in object face and word recognition. • The dorsal or ‘where’ stream runs from the primary visual cortex to superior regions of the parietal lobe and is involved with locating objects in space (Ungerleider & Mishkin, 1982). • Apraxic patients can recognise objects and visual agnosic patients can carry out actions suggesting that the visual system can break down into modules for perception and action.

5. Balint’s syndrome • Balint’s syndrome results from bilateral parietal lobe damage and manifests as a disorder of spatial attention and visually guided reaching. • Patients show a deficit called optic ataxia which is an inability to perform coordinated voluntary eye movements in order to reach for an object. • The lesion also impairs the ability to correctly shape the hand called prehensile movements. • The kinematic of reaching is altered, increased duration, lower velocity, and longer deceleration.

6. Optic Ataxia • As optic ataxic patients have trouble reaching for objects and adjusting their grasp, this syndrome it is not just a problem with spatial vision but also with action (visuo-motor skills). • Recent models of visual information processing assume that optic ataxia results from a deficit to the dorsal pathway which connects pre-striate areas to the posterior part of the parietal lobe. • This pathway is involved in the perception of spatial relations and object attributes which are used for controlling co-ordinated movements.

7. Where or how? • Goodale and Milner (1992; Milner & Gooodale, 1993) argue the dorsal stream in the parietal lobe is used for the spatial control of action. • Pragmatic motor representations (praxicons) are stored in the parietal lobe and these give guidance about ‘how’ to act toward an object. • Data from double dissociations between action and perception impairments reported in the neuropsychological literature support this (eg. Jeannerod, 1986; Perenin and Vighetto, 1998).

8. Patient DF • A visual apperceptive agnosic with a lesion in left temporal lobe (ventral area) could perform unconscious actions (e.g. pick up objects) but was impaired with actions requiring conscious attention e.g. making a cup of coffee (c.f., IA). • Goodale and Milner argue that patient DF could use an intact parietal ‘how’ system to carry out covert actions that did not require attention. • DF suggests that correct movement of a limb does not require overt visual cognition that may be used if the action requires use of an object.

10. Action • All parts of the brain (lobes) are used for action. • Vision guides most skilled actions (occipital). • Actions require information about the location of hands and limbs and the relative position of an object to the body in space (parietal lobe). • Actions also require access to knowledge of what an object actually is (temporal lobe). • The frontal lobes are used for the planning, execution and regulation of all skilled actions. • Conscious control over action a frontal activity?

12. Apraxia • Apraxia first characterised by Hugo Liepmann at the beginning of the 20th century as a loss of the ability to perform learned skilled movements. • Praxis is the word for skilled movement ability and praxicons are the cognitive schemata that allow for specific skilled actions to be performed. • Apraxia is not due to an impairment of motor skills (strength, reflexes, co-ordination), sensory loss (visual agnosia), a comprehension deficit or the loss of motivation to perform skilled actions.

13. Types of apraxia • Motor • inability to make precise fine motor movements. • Ideomotor • inability to carry out an action to command (hands). • Ideational • inability to create a plan for a movement sequence. • Callosal apraxia • Dissconnection of hemispheres -> the alien hand.

14. Anatomy and pathology • Reaching-grasping movements and gesture production depend on function of neurons in: • posterior parietal cortex (especially the left) • premotor cortex • motor cortical areas • corpus callosum • Lesions in any of these regions can disrupt skilled movement and produce several neuropsychological syndromes including action disorganisation syndrome (ADS).

15. Motor Apraxia • Patient is unable to make precise movements with objects from pantomime, imitation and actual use of the object (doing up buttons). • Results from damage to the precentral gyrus (premotor) and the part of the motor cortex on that is on the contralateral side to damage. • Typically affects fine motor movements and is evident on tasks like finger tapping. • It affects automatic and voluntary movements.

16. Ideomotor Apraxia (IMA) • Cannot carry out actions to command but may perform the action spontaneously e.g. smiling. • Patients fail in the pretend use of objects • production of symbolic gestures (e.g., saluting); • unable to imitate symbolic and nonsense gestures; • impaired in producing pantomimes of object use. • Patients have difficulties when asked to orient their hands in space to produce a gesture. • Suggests a deficit to knowledge about how to perform specific movement sequences.

17. Ideational Apraxia (IA) • Patient can imitate and carry out an action to command but cannot perform a sequence of actions leading to a goal (e.g. making coffee). • They fail in the actual use of objects and show inappropriate use of objects and object selection; • unable to perform a series of actions which they may be able to produce individually; • when making a cup of coffee they correctly perform each step, but will fail in sequencing them, such as pouring water before opening the coffee maker • Suggests a deficit to skilled use of objects.

18. Callosal apraxia • Liepmann (1908) reported a right handed man with a lesion to the corpus callosum (stroke). • He could use his right hand to perform actions but he could not use his left hand to carry out purposeful movements from verbal command. • Showed apraxia and agraphia of the left hand. • Leipmann argued that this was a type of disconnection syndrome whereby left verbal hemisphere was disconnected from the right hemisphere (used for moving the left hand).

19. A dissconnection syndrome • Liepmann’s theory of apraxia assumed that the left parietal cortex (BA 40) is the brain region that controls complex movement and proposed that there is a connection to the right frontal lobe via the corpus callosum. • Damage to the corpus callosum disconnects the praxicons in the left parietal lobe from the movement plans located in the right frontal lobe needed to move the left hand. • Also Geschwind (1965) and Heilman (1979).

21. Split brain patients • A commissurotomy of the corpus callosum. • Performed for intractable epilepsy. • Split field technique. • Patients showed callosal apraxia and tactile agnosia when using the left hand. • Due to a disconnection between the verbal left hemisphere and the right hemisphere that is used to control movement of the left hand.

23. The ‘Alien’ Hand • Involuntary, compulsive use of utilitarian articles placed within the patient’s reach with the left hand - this is called utilisation behaviour. • There is inter-manual conflict whereby the left hand tries to stop actions carried out by the right hand - the alien hand is like a ‘bad baby’. • There is also a belief that the hand is out of the patients own control and in extreme form that the hand does not belong to the patient at all. • Two selves in the one brain?

24. Action and consciousness • There is a tendency for the arm to drift off and assume odd postures especially when the P’ts eyes are closed or attention is diverted. • Patient reports that they cannot command the alien hand to carry out a voluntary movement. • There is a tendency for the patient to control the hand by restraining the arm physically. • The alien hand can also execute purposeful movements and these appear to be entirely dissociated from conscious volitional control.

25. Frontal lobes and action • The alien hand was originally thought to result from a specific lesion to the anterior part of the corpus callosum - and this is called the genu. • The neuro-anatomical data now suggest that the syndrome is due to a lesion of the right frontal cortex - the supplementary motor area (SMA). • Neuropsychologists now believe the alien hand to be a deficit in the voluntary inhibition of movement in either the left or right SMA. • Shallice (1988) has developed a theory of how actions are executed by the frontal cortex.

26. Multiple action systems? • Studies of patients with alien hand syndrome suggest that knowledge about how to perform an action with each hand may be replicated in two separate systems in each hemisphere. • Praxicons stored in the parietal lobe activate purposeful actions in both hemispheres but there is parallel suppression of activity in the contra-lateral SMA as required for movement. • The alien hand usually becomes active when a sequence of movements using the dominant hand is required but can affect the other hand.

27. Multiple action systems? • Liepmann suggested that apraxia can arise from damage to two different action systems: • Conceptual level: contains ‘movement formulae’ that represent knowledge about sequences of action for learned movements with specific objects (such as knowledge about tool function). • Production level: contains stored ‘action motor programmes’ that can be translated into skilled behaviour via motor neurones that innervate parts of the body used to carry out the action.

28. Cognitive models of action • Rothi et al (1991) recently proposed a cognitive model of action with two systems: a conceptual (semantic) based action system and a sensori-motor (non-semantic) based action system. • If there are two action systems then we should find patients who are impaired with actions that require object knowledge (conceptual) but not impaired when imitating meaningless actions. • Conversely, there should be patients who cannot imitate meaningless actions but who can perform actions with objects correctly (IA).

29. Conceptual apraxia • Damage to the semantic action system results in a deficit with the correct use of well known objects (e.g., tools) and this type of apraxia has been called conceptualapraxia. • This type of apraxia is reported in patients who have semantic dementia (progressive loss of knowledge about objects, faces and words). • These patients can imitate meaningless actions and display preserved action sequences with novel objects that they have never seen before (e.g. Buxbaum et al, 1997; Hodges et al, 1999).

30. Evidence for a unitary system • Hodges et al (1999) found spared knowledge of actions depends upon access to preserved object knowledge in semantic dementia. • Castiello et al. (1995) report a patient LP with apraxia who made actions in response to two objects only if the objects were semantically related (e.g. pen and paper) suggesting that the action system depends upon object knowledge for coherent movement. • Access to action knowledge depends upon object knowledge - at least for some actions.

31. Summary • Studies of apraxic patients show that knowledge about where an object is in space and how to act upon objects is represented in the parietal lobe. • Studies of alien hand patients suggest that there might be two types of consciousness for who show conceptual and/or motor apraxia casting doubt on the early subtypes. • Cognitive neuropsychological studies of patients with brain damage suggest the normal action system is modular and can be dissociated into at least two pathways (semantic & non-semantic).

32. References • Castiello U, Scarpa M, Bennet K. (1995). A brain damaged patient with an unusual perceptuo-motor deficit. Nature, 374, 805-808. • Goodale, M. A Milner, A. D Jakobson, L. S and Carey, D. P. A (1991). A neurological dissociation between perceiving objects and grasping them. Nature, 349, 154-6. • Hodges JR, Spatt J, Patterson K. (1999). ‘What’and ‘How’: Evidence for the dissociation of object knowledge and mechanical problem-solving skills in the human brain. Proceedings from the National Academy of Sciences of the USA; 96, 9444-9448. • Ochipa C, Rothi LJG, Heilman KM. (1992). Conceptual apraxia in Alzheimer’s disease. Brain, 115, 1061-1071. • Rothi LJG, Ochipa C, Heilman KM. (1991). A cognitive neuropsychological model of limb praxis. Cognitive Neuropsychology, 8, 443-458.