We review evidence for partially segregated networks of brain areas that carry out different attentional functions. One system, which includes parts of the intraparietal cortex and superior frontal cortex, is involved in preparing and applying goal-directed (top-down) selection for stimuli and responses. This system is also modulated by the detection of stimuli. The other system, which includes the temporoparietal cortex and inferior frontal cortex, and is largely lateralized to the right hemisphere, is not involved in top-down selection. Instead, this system is specialized for the detection of behaviourally relevant stimuli, particularly when they are salient or unexpected. This ventral frontoparietal network works as a 'circuit breaker' for the dorsal system, directing attention to salient events. Both attentional systems interact during normal vision, and both are disrupted in unilateral spatial neglect.

Control of goal-directed and stimulus-driven attention in the brain

Co-Planar Stereotaxic Atlas of the Human Brain—3-Dimensional Proportional System: An Approach to Cerebral Imaging, J. Talairach, P. Tournoux. Georg Thieme Verlag, New York (1988), 122 pp., 130 figs. DM 268

A category of stimuli of great importance for primates, humans in particular, is that formed by actions done by other individuals. If we want to survive, we must understand the actions of others. Furthermore, without action understanding, social organization is impossible. In the case of humans, there is another faculty that depends on the observation of others' actions: imitation learning. Unlike most species, we are able to learn by imitation, and this faculty is at the basis of human culture. In this review we present data on a neurophysiological mechanism--the mirror-neuron mechanism--that appears to play a fundamental role in both action understanding and imitation. We describe first the functional properties of mirror neurons in monkeys. We review next the characteristics of the mirror-neuron system in humans. We stress, in particular, those properties specific to the human mirror-neuron system that might explain the human capacity to learn by imitation. We conclude by discussing the relationship between the mirror-neuron system and language.

The mirror-neuron system.

The anterior insular cortex (AIC) is implicated in a wide range of conditions and behaviours, from bowel distension and orgasm, to cigarette craving and maternal love, to decision making and sudden insight. Its function in the re-representation of interoception offers one possible basis for its involvement in all subjective feelings. New findings suggest a fundamental role for the AIC (and the von Economo neurons it contains) in awareness, and thus it needs to be considered as a potential neural correlate of consciousness.

How do you feel--now? The anterior insula and human awareness.

Prior to the twentieth century, theories of knowledge were inherently perceptual. Since then, developments in logic, statis- tics, and programming languages have inspired amodal theories that rest on principles fundamentally different from those underlying perception. In addition, perceptual approaches have become widely viewed as untenable because they are assumed to implement record- ing systems, not conceptual systems. A perceptual theory of knowledge is developed here in the context of current cognitive science and neuroscience. During perceptual experience, association areas in the brain capture bottom-up patterns of activation in sensory-motor areas. Later, in a top-down manner, association areas partially reactivate sensory-motor areas to implement perceptual symbols. The stor- age and reactivation of perceptual symbols operates at the level of perceptual components - not at the level of holistic perceptual expe- riences. Through the use of selective attention, schematic representations of perceptual components are extracted from experience and stored in memory (e.g., individual memories of green, purr, hot). As memories of the same component become organized around a com- mon frame, they implement a simulator that produces limitless simulations of the component (e.g., simulations of purr). Not only do such simulators develop for aspects of sensory experience, they also develop for aspects of proprioception (e.g., lift, run) and introspec- tion (e.g., compare, memory, happy, hungry). Once established, these simulators implement a basic conceptual system that represents types, supports categorization, and produces categorical inferences. These simulators further support productivity, propositions, and ab- stract concepts, thereby implementing a fully functional conceptual system. Productivity results from integrating simulators combinato- rially and recursively to produce complex simulations. Propositions result from binding simulators to perceived individuals to represent type-token relations. Abstract concepts are grounded in complex simulations of combined physical and introspective events. Thus, a per- ceptual theory of knowledge can implement a fully functional conceptual system while avoiding problems associated with amodal sym- bol systems. Implications for cognition, neuroscience, evolution, development, and artificial intelligence are explored.

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Perceptual symbol systems.

A 46-year-old patient with a lesion limited to the left retrorolandic area without involvement of the prerolandic motor strip was examined. Anaesthesia to tactile, warm, cold, and painful stimuli was complete for the right hand and wrist. Position sense was abolished for the right wrist and finger joints. Performance of the right hand in motor tasks was severely impaired. Simple visual and auditory reaction times were lengthened. Sustaining a constant level of force was impossible. In the absence of visual feedback, only simple, monoarticular movements could be correctly executed; more complex movements requiring coordination between several joints, such as prehension, were poorly, or not, performed. The role of somatosensory cortex in conveying kinaesthetic input to the motor areas and the importance of vision in substituting for kinaesthetic loss, are discussed.

The control of hand movements in a case of hemianaesthesia following a parietal lesion.

Sense of body and sense of action both contribute to self-recognition

Three apraxic patients with lesions in the left parietal cortex were required to execute finger movements with either hand, while the visual feedback they received about the movement was manipulated systematically We used a device which allowed us to present on a video monitor either the patient's hand or the examiner's hand simultaneously performing an identical or a different movement In each trial, patients were required to decide whether the hand shown on the screen was their own or not Hand movements produced in response to verbal command included simple (single-finger extension) and complex gestures (multi-finger extension) Ownership judgements were analysed and compared with those produced by six normal controls and two non-apraxic neurological patients Apraxic patients and controls accurately recognized their own hand on the screen (own movement condition) and correctly identified the viewed hand as the examiner's when it performed a movement different from their own movement (incongruent movement condition) However, when the viewed hand was the examiner's hand executing their own movement (congruent movement condition), apraxic patients were significantly more impaired than controls When the results were analysed as a function of gesture type, the number of correct responses was significantly lower for apraxic patients with respect to controls only for complex gestures Interestingly, when patients executed the finger gestures inaccurately, they still failed to recognize the examiner's hand as alien, and claimed that the correct movement presented on the screen was their own These results confirm that parietal lesions alter the representational aspects of gestures, and suggest a failure in evaluating and comparing internal and external feedback about movement We conclude that the parietal cortex plays an important role in generating and maintaining a kinaesthetic model of ongoing movements

Perception of self-generated movement following left parietal lesion.

Motor imagery of a lateralized sequential task is asymmetrically slowed in hemi-Parkinson's patients

The purpose of this study was to identify the functional anatomy of the mechanisms involved in visually guided prehension and in object recognition in humans. The cerebral blood flow of seven subjects was investigated by positron emission tomography. Three conditions were performed using the same set of stimuli. In the ‘grasping’ condition, subjects were instructed to accurately grasp the objects. In the ‘matching’ condition, subjects were requested to compare the shape of the presented object with that of the previous one. In the ‘pointing’ condition (control), subjects pointed towards the objects. The comparison between grasping and pointing showed a regional cerebral blood flow (rCBF) increase in the anterior part of the inferior parietal cortex and part of the posterior parietal cortex. The comparison between grasping and matching showed an rCBF increase in the cerebellum, the left frontal cortex around the central sulcus, the mesial frontal cortex and the left inferior parietal cortex. Finally, the comparison between matching and pointing showed an rCBF increase in the right temporal cortex and the right posterior parietal cortex. Thus object-oriented action and object recognition activate a common posterior parietal area, suggesting that some kind of within-object spatial analysis was processed by this area whatever the goal of the task. A large body of anatomical data indicate that connections within the monkey visual cortex are organized along two main streams of projections. Both streams originate from the primary visual areas: the dorsal stream goes through extrastriate visual areas and reaches the associative parietal areas, whereas the ventral stream reaches the inferotemporal cortex (Mishkin et al., 1983;

/pdf/visual-pathways-for-object-oriented-action-and-object-331wqhm77u.pdf

Marc Jeannerod

Papers

The control of hand movements in a case of hemianaesthesia following a parietal lesion.

Sense of body and sense of action both contribute to self-recognition

Perception of self-generated movement following left parietal lesion.

Motor imagery of a lateralized sequential task is asymmetrically slowed in hemi-Parkinson's patients

Visual pathways for object-oriented action and object recognition: functional anatomy with PET.