[Frontal lobe, executive functions and cognitive control]. / Lobe frontal, fonctions exécutives et controle cognitif.

The approach of executive functions began with the early description of behavioural disorders induced by frontal damage. The development of neuropsychology has led to the description of a large variety of cognitive disorders. The interpretation in cognitive terms of these disorders has emphasized the critical impairment of executive functions which are involved in non-routine situations. The role of working memory, initially suggested by animal studies, has also largely influenced theoretical approaches. Numerous studies have been interpreted within the theoretical frameworks developed by Shallice and by Baddeley. A large amount of studies have allowed the specification of control processes (initiation, inhibition...). Recent studies are beginning to investigate cognitive disorders underlying behavioural changes such as deficits of emotional, social and metacognitive processes. In addition these studies seriously question the assumption of a unique central control system. These studies have deeply influenced the clinical approach, the assessment and the diagnosis of executive syndrome. For clinical practice, these data lead to favour specific assessment of some key behavioural and cognitive deficits based on a battery of tests and structured interview of an informant.

Effect of distorted visual feedback on the sense of agency.

It has been hypothesized that an internal model is involved in controlling and recognizing one's own actions (action attribution). This results from a comparison process between the predicted sensory feedback of the action and its real sensory consequences. The aim of the present study is to distinguish the respective importance of two action parameters (time and direction) on such an attribution judgment. We used a device that allows introduction of discordance between the movements actually performed and the sensory feedback displayed on a computer screen. Participants were asked to judge whether they were viewing 1) their own movements, 2) their own movements modified (spatially or temporally displaced), or 3) those of another agent (i.e, the experimenter). In fact, in all conditions they were only shown their own movements either unaltered or modified by varying amounts in space or time. Movements were only attributed to another agent when there was a high spatial discordance between participants' hand movements and sensory feedback. This study is the first to show that the direction of movements is a cardinal feature in action attribution, whereas temporal properties of movements play a less important role.

Visual cognition: a new look at the two-visual systems model.

In this paper, we argue that no valid comparison between visual representations can arise unless provision is made for three critical properties: their direction of fit, their direction of causation and the level of their conceptual content. The conceptual content in turn is a function of the level of processing. Representations arising from earlier stages of processing of visual input have very little or no conceptual content. Higher order representations get their conceptual content from the connections between visual cognition and other parts of the human cognitive system. The two other critical properties of visual representations are their mind/world direction of fit and their mind/world direction of causation. The output of the semantic processing of visual input has a full mind-to-world direction of fit and a full world-to-mind direction of causation: it visually registers the way the world is and is caused by what it represents. The output of the pragmatic processing yields information for the benefit of intentions, which clearly have a world-to-mind direction of fit and a mind-to-world direction of causation. An intention is both the representation of a goal and a cause of the transformation of a goal into a fact. These properties segregate representations specialized for perception from those specialized for action. Perception implies comparison between simultaneously represented and analyzed objects: hence, object perception presupposes the representation of spatial relationships among objects in a coordinate system independent from the perceiver. Spatial relationships carry cues for attributing meaning to an object, so that their processing is actually part of semantic processing of visual information. These considerations lead to a re-evaluation of the role of the two classical pathways of the human visual system: the ventral and the dorsal cortical pathways. The parietal lobe, which has been identified with the dorsal pathway, cannot be considered as a unitary entity with a single function. The superior parietal lobule carries visuomotor processing, a non-lateralized process. The right inferior parietal lobule contributes to the perception of spatial relationships, a process with a mind-to-world direction of fit and a world-to-mind direction of causation. Finally, the left inferior parietal lobule contributes to still another type of representation, related to visually goal-directed action, i.e., with both a world-to-mind direction of fit and a mind-to-world direction of causation.

Influence of mental motor imagery on the execution of a finger-to-thumb opposition task.

The present fMRI study compares regional distribution of the cortical activity during the execution of unilateral hand movements (finger-to-thumb opposition) preceded or not by their motor simulation (S + E and E condition, respectively). The results show that, overall, the number and the spatial distribution of activated voxels are both increased in the S + E with respect to the E condition. The motor performance preceded by mental rehearsal is related to selective increase of the cortical activity. Among the motor areas that are found active during the simple motor execution a significant enhancement of functional activation during the S + E condition ipsilateral primary motor regions (M1). The activity increase may be accounted by a sort of neural recruiting that is made possible by the overlapping of cortical networks involved in both motor output and motor imagery. The beneficial effects of "mental practice" on the physical performance may rely to the close temporal association between motor rehearsal and actual performance.

The role of proprioception in action recognition.

This study aimed at evaluating the role of proprioception in the process of matching the final position of one's limbs with an intentional movement. Two experiments were realised with the same paradigm of conscious recognition of one's own limb position from a distorted position. In the first experiment, 22 healthy subjects performed the task in an active and in a passive condition. In the latter condition, proprioception was the only available information since the central signals related to the motor command were likely to be absent. The second experiment was realised with a deafferented patient who suffers from a complete haptic deafferentation, including loss of proprioception. The results first argue in favour of a dominant role of proprioception in action recognition, but they also stress the possible role of central signals. The process of matching the final position of one's limbs with an intended movement and thus of action recognition would be achieved through a comparison process between the predicted sensory consequences of the action, which are stored in its internal model, and the actual sensory consequences of that action.

Modulating the experience of agency: a positron emission tomography study.

This study investigated agency, the feeling of being causally involved in an action. This is the feeling that leads us to attribute an action to ourselves rather than to another person. We were interested in the effects of experimentally modulating this experience on brain areas known to be involved in action recognition and self-recognition. We used a device that allowed us to modify the subject's degree of control of the movements of a virtual hand presented on a screen. Four main conditions were used: (1) a condition where the subject had a full control of the movements of the virtual hand, (2) a condition where the movements of the virtual hand appeared rotated by 25 degrees with respect to the movements made by the subject, (3) a condition where the movements of the virtual hand appeared rotated by 50 degrees, and (4) a condition where the movements of the virtual hand were produced by another person and did not correspond to the subject's movements. The activity of two main brain areas appeared to be modulated by the degree of discrepancy between the movement executed and the movement seen on the screen. In the inferior part of the parietal lobe, specifically on the right side, the less the subject felt in control of the movements of the virtual hand, the higher the level of activation. A reverse covariation was observed in the insula. These results demonstrate that the level of activity of specific brain areas maps onto the experience of causing or controlling an action. The implication of these results for understanding pathological conditions is discussed.

The prefrontal cortex and conscious monitoring of action: an experimental study.

To investigate the role of the prefrontal cortex in conscious monitoring, we used an experimental paradigm generating a conflict between the action planned and the sensory-motor feedback. We analyzed the acquisition of explicit knowledge of the strategy for resolving the conflict and its influence on motor adaptation. Twenty patients with frontal lobe lesions and 18 controls had to trace a sagittal line with a stylus on a graphics tablet. A mirror on which the traced line, processed by a computer, was projected hid the hand. A mask limited visual feedback to the last third of the trajectory. Without informing the subjects, the line traced was modified by introducing a bias of 24 degrees to the right. To succeed in the task, subjects had to modify their motor program and to deviate their trajectory in the opposite direction. Conscious elaboration of the strategy was evaluated by the number of trials needed to explicitly report the required deviation. Three groups of patients were distinguished: (1). with normal explicit strategy; (2). with delayed explicit strategy, and (3). without explicit strategy at the last trial. They significantly differed by the severity of the dysexecutive syndrome, particularly of environmental adherence. Motor adaptation was evaluated by the area between the line traced and the ideal line to compensate for the deviation. In patients with normal elaboration of the strategy, motor control was similar to that of controls, but it was severely disturbed in the other two groups. These results suggest the involvement of the prefrontal cortex in conscious motor monitoring.

Visuo-motor control of the ipsilateral hand: evidence from right brain-damaged patients.

We investigated the extent to which the right hemisphere is involved in the control of the ipsilateral hand by analysing the kinematics of right-hand prehension in right brain-damaged (RBD) patients. We required patients to grasp one of five possible objects, equally-sized and distributed over a 40 degrees wide workspace. With the purpose of investigating the right hemisphere contribution to the on-line visuo-motor control, we also assessed patients' ability to correct their movement "in-flight", in response to a sudden change of object position. Patients' performance was compared to that of aged-matched controls. A Younger group of healthy subjects, matching the population classically tested on double-step paradigms, was also evaluated to fully assess whether patients' kinematics could be partially due to normal ageing. As a further aim, the possible influence of hemispatial neglect was evaluated by comparing the performances of right brain-damaged patients with and without neglect. In normal subjects, the results confirmed and extended the notion of (a). positional tuning of grip formation, and (b). fast reactions following a change in object position. In addition, subtle effects of ageing on visuo-motor behaviour were shown by less efficient movement correction in the Elderly group. Patients executing reach-to-grasp actions into the left contralesional hemispace were selectively affected in both temporal and spatial aspects of movements. While their performances were relatively well preserved in the right hemispace, patients did not show positional tuning of grip formation, nor fast corrections of their movements when acting in the left hemispace. Interestingly, similar deficits were found irrespective of the presence of neglect. These results show that the right hemisphere contributes to the processing of visuo-motor information that is necessary for executing actions with the ipsilateral hand in the contralateral space.

Anticipating incoming events: an impaired cognitive process in schizophrenia.

Intentions are central to guiding actions to their completion because they generate expectations which precede the realization of a task. This ability to manage time was investigated by using a cognitive task which involves several highly integrated processes: sequential learning, explicit processing, and working memory. In this task, participants are required to explicitly learn a repeating color sequence before receiving an instruction to give an anticipatory motor response concerning the next element. Two types of sequences (temporal and spatial) and three experimental conditions were tested in both a group of normal participants and a group of schizophrenic patients. Schizophrenics were included because their condition is known to alter conscious executive function. Our results showed that schizophrenic patients have a strong deficit in performing anticipation tasks. Although they learned the sequences almost normally, their anticipatory ability was reduced in comparison to normal participants in all the tested conditions. These results expand the notion of a working memory deficit in schizophrenia and bear strong implications for understanding executive disorders observed in such patients.

Self-monitoring in schizophrenia revisited.

According to a widespread theory, the first-rank symptoms such as delusions of control or thought insertion met in schizophrenia result from a failure in predicting the consequences of an action on the basis of a forward model based of the intended motor commands (efference copy). This assumption of an impairment in the central monitoring of their own actions is inferred from experiments showing that it is more difficult for schizophrenic patients than for controls to correct erroneous movements in the absence of visual feedback. In our study, 19 schizophrenic patients (10 with Schneiderian symptoms and nine without) and 19 paired control subjects were subjected to a sensorimotor adjustment task to reassess this hypothesis. We show that the patients who succeeded the task not differently from the control subjects were those who were aware of the manual correction (n = 9). Surprisingly, most of them presented Schneiderian symptoms. This suggests that the experience of alien control observed in certain schizophrenic patients cannot be directly related to an underlying cognitive deficit in the conscious monitoring of their own actions.

Preserved adjustment but impaired awareness in a sensory-motor conflict following prefrontal lesions.

Control of action occurs at different stages of the executive process, in particular at those of sensory-motor integration and conscious monitoring. The aim of this study was to determine the implication of the prefrontal cortex in the control of action. For that purpose, we compared the performance of 15 patients with frontal lobe lesions and 15 matched controls on an experimental paradigm generating a conflict between the action planned and the sensory-motor feedback. Subjects had to trace a sagittal line with a stylus on a graphic tablet. The hand was hidden by a mirror on which the traced line, processed by a computer, was projected. Without informing the subjects, the line traced was modified by introducing a bias to the right, which increased progressively from 2 degrees to 42 degrees. To succeed the task, subjects had to modify their motor program and deviate their hand in the opposite direction. The sensory-motor adjustment to the bias was evaluated by the surface between the line traced and the ideal line to compensate for the deviation. The awareness of the conflict was measured by the angle of the bias at which subjects expressed the feeling that the line they traced was not the same as the line they saw. The deviation was similarly compensated for by patients and controls until 24 degrees. Then 14 controls but only 3 patients were aware of a conflict. After that, the variability of performance increased significantly for the unaware patients. These results suggest that the prefrontal cortex is required at the level of conscious monitoring of actions, but not at the level of sensory-motor integration.

Neural simulation of action: a unifying mechanism for motor cognition.

Paradigms drawn from cognitive psychology have provided new insight into covert stages of action. These states include not only intending actions that will eventually be executed, but also imagining actions, recognizing tools, learning by observation, or even understanding the behavior of other people. Studies using techniques for mapping brain activity, probing cortical excitability, or measuring the activity of peripheral effectors in normal human subjects and in patients all provide evidence of a subliminal activation of the motor system during these cognitive states. The hypothesis that the motor system is part of a simulation network that is activated under a variety of conditions in relation to action, either self-intended or observed from other individuals, will be developed. The function of this process of simulation would be not only to shape the motor system in anticipation to execution, but also to provide the self with information on the feasibility and the meaning of potential actions.

Defective recognition of one's own actions in patients with schizophrenia.

OBJECTIVE: The possibility that delusions of influence could be related to abnormal recognition of one's own actions was investigated in persons with schizophrenia. METHOD: Schizophrenic patients with (N=6) and without (N=18) delusions of influence were compared with normal subjects (N=29) on an action recognition task. The image of a virtual right hand holding a joystick was presented to the subjects through a mirror so that the image was superimposed on their real hand holding a real joystick. Subjects executed discrete movements in different directions. Angular biases and temporal delays were randomly introduced in some trials, such that the movement of the virtual hand departed from the movement executed by the subjects. After each trial, subjects were asked whether the movement they saw was their own. RESULTS: Compared with normal subjects, both patient groups made significantly more recognition errors in trials with temporal delays. In trials with angular biases, the error rate of patients with delusions of influence significantly differed from that of comparison subjects and from that of patients without delusions of influence. CONCLUSIONS: The findings support the hypothesis that delusions of influence are associated with a quantifiable difficulty in correct self-attribution of actions. This difficulty may be related to a specific impairment of a neural action attribution system.

Orientation of the opposition axis in mentally simulated grasping.

Five normal subjects were tested in a simulated grasping task. A cylindrical container filled with water was placed on the center of a horizontal monitor screen. Subjects used a precision grip formed by the thumb and index finger of their right hand. After a preliminary run during which the container was present, it was replaced by an image of the upper surface of the cylinder appearing on the horizontal computer screen on which the real cylinder was placed during the preliminary run. In each trial the image was marked with two contact points which defined an opposition axis in various orientations with respect to the frontal plane. The subjects' task consisted, once shown a stimulus, of judging as quickly as possible whether the previously experienced action of grasping the container full of water and pouring the water out would be easy, difficult or impossible with the fingers placed according to the opposition axis indicated on the circle. Response times were found to be longer for the grasps judged to be more difficult due to the orientation and position of the opposition axis. In a control experiment, three subjects actually performed the grasps with different orientations and positions of the opposition axis. The effects of these parameters on response time followed the same trends as during simulated movements. This result shows that simulated hand movements take into account the same biomechanical limitations as actually performed movements.

Is the organisation of goal-directed action modality specific? A common temporal structure.

With the help of kinematic analysis, the temporal organization of the complex daily activity 'drinking from a bottle with a glass' was described in detail. The analysis focused on the sequential action structure, the prehensile acts, and the bimanual coordination as well as on the effect of different instruction modalities on these parameters to explore the underlying representation for this complex action. Movements of the two arms were recorded in three-dimensional space with the help of an optoelectronic device in 12 normal subjects under four conditions: (1) action pantomime after verbal instruction; (2) action imitation after observation of the action performed by the experimenter without the objects; (3) action pantomime while seeing, but not touching the objects; and finally (4) action execution with objects. Despite high execution variability, the temporal structure of the action could be precisely described by the relative duration and peak velocity of action segments, by the MGA-object size-correlation, and by linear regression analysis between the onsets of functionally related action segments. A similar structure of the action as characterized by these kinematic parameters was retained across different instruction modalities. Only when the action was executed with the objects, the interval between the movement onsets of either hand and the peak velocity of the manipulative acts were reduced, while no change was observed across the other three instruction modalities. This stability of the temporal structure suggests the existence of a level in the representation of an action where all the modalities converge.

Changes in breathing during observation of effortful actions.

Respiration and heart rates were recorded in normal subjects watching effortful actions produced by an actor in front of them. Subjects remained immobile throughout. Two experiments were performed. In experiment 1, subjects watched a weight-lifting performance, either static or dynamic, with increasing weights. In experiment 2, they watched a walking/running performance on a treadmill moving at increasing speed. In both experiments, no change was found in observers' heart rate. By contrast, consistent changes were found in respiration rate. These changes tended to follow the exercise rhythm of the actor, specially during accelerated running (from 2.5 to 10 km/h) where respiration rate increased linearly with speed of the treadmill. Average maximum increase ranged between 25 and 30% above resting rate. This finding demonstrates activation of central mechanisms related to action performance during observation of effortful actions. It could represent a basis for understanding and imitating actions performed by other people.

Mental imaging of motor activity in humans.

Motor imagery corresponds to a subliminal activation of the motor system, a system that appears to be involved not only in producing movements, but also in imagining actions, recognising tools and learning by observation, as well as in understanding the behaviour of other people. Recent advances in the field include the use of techniques for mapping brain activity and probing cortical excitability, as well as observation of brain lesioned patients during imaging tasks; these advances provide new insights into the covert aspects of motor activity.

Perception of self-generated movement following left parietal lesion.

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.

Human brain activity related to the perception of spatial features of objects.

The role of the parietal cortex in visuospatial analysis of object was investigated by cerebral blood flow measurements in seven objects using positron emission tomography. Data were acquired while subjects performed a matching task requiring the discrimination of simultaneously presented objects based on one of their spatial properties. Three properties were studied separately during three scanning conditions repeated twice:surface orientation, principal axis orientation, and size. Scans were also obtained during a sensorimotor control task (similar visual stimulation, same motor action, voluntary saccades toward each object) as well as during rest (no stimulation, eyes closed). Compared to rest, the three property matching tasks showed the same pattern of activation: the whole occipital lobe, the right intraparietal sulcus (IPS), and the right occipitotemporal (OT) junction. Compared to the control condition, only right IPS and OT junction were significantly activated during discrimination of the spatial properties. The IPS focus was located between the superior parietal lobule and the angular gyrus, and the OT activation overlapped the posterior part of the inferior temporal gyrus and the middle occipital gyrus. These results indicate that discrimination of spatial attributes requires the activation of both the parietal and the temporal cortices of the right hemisphere and provide further evidence that the IPS plays a critical role in visuospatial analysis of objects.