The impulsive brain: Neural underpinnings of binge eating behavior in normal-weight adults.

Converging evidence suggests that dysfunctional inhibitory control might be at the roots of overeating and binge eating disorder (BED). The majority of these results stems from studies on obese populations, however we hypothesized that potential prodromes might be evident also in non-clinical conditions, when binge eating episodes are present (without a diagnosis of BED) and a normal Body Mass Index is preserved. To explore this issue, brain activity of 42 normal weight individuals with and without binge eating episodes (21 binge eaters and 21 non-binge eaters, BE and non-BE respectively) was assessed by means of functional magnetic resonance imaging (fMRI) during response inhibition tasks. We adopted a food-modified version of a go/no-go (GNG) and stop signal task (SST): these tasks investigate different aspects of inhibitory control (action restraint and cancellation) that have been rarely studied in the same individuals but that are known to involve different neural networks. In addition, impulsivity traits were assessed with self-report instruments. Despite similar behavioral performances, the two groups differed in trait impulsivity and brain activity. The fMRI results revealed differential engagement of fronto-striatal regions between the groups during the tasks. The BE group, compared to non-BE, showed lower activation of the right middle frontal gyrus (MFG) and Putamen during the GNG task, and higher activation of the left MFG during the SST. These findings provide evidence of a dissociation of the neural underpinnings of action restraint and cancellation in impulsive individuals. Moreover, they add support to the hypothesis that impulsivity may be a possible hallmark of binge eating behavior (in the absence of weight or full-blown eating disorders) and yield new insights on the role of regions typically involved in response inhibition and selection as possible substrates of impulsive eating.

Parkinson's disease: reorganization of the reach to grasp movement in response to perturbation of the distal motor patterning.

This study assessed the kinematic changes to the reach to grasp movement in response to a perturbation of object size in 15 Parkinson's disease (PD) and 15 control subjects. For non-perturbed trials subjects reached 35 cm to grasp and lift either an illuminated small (0.7 cm) or large (8 cm) diameter cylinder. For perturbed trials (20%), illumination shifted unexpectedly from the small to the large or from the large to the small cylinder at the onset of the reach. For Condition One trials subjects were given no instructions as to which grasp to use. With perturbation, they thus naturally changed grasp from precision grip to whole hand prehension or vice versa. The results for the PD subjects indicated a slowness at the transition from one to another grasp. This contrasted to the smooth transitions when perturbation required only a change of grasp aperture (precision grip--Condition Two; whole hand prehension--Condition Three). PD subjects thus showed dysfunction in the suppression/activation of different grasp programs rather than deficits in the on-line modification of an operating program.

Perceiving an entire object and grasping only half of it.

A single case study is presented of an unusual dissociation between the sensory perception of an object and the grasping action towards the same object. The patient IW was found at age 74 to have spent all his life without the left parietal lobe, as a result of a congenital peri-natal insult. IW does not show any signs of sensory dysfunction, but he has a persistent motor bias that arises during movement towards objects. When IW was required to reach and grasp stationary and rotating objects, he consistently grasped the objects to the left side. Thus, it appears that information that is available at a sensory level can nevertheless be unavailable at a motor level. Our findings not only help to clarify the functions of the parietal lobe, but also show that lesions in this area are linked specifically to a process of response performance, which is fundamental for our understanding of visuomotor control.

Temporal dissociation of the prehension pattern in Parkinson's disease.

This study assesses the reach to grasp movement of eight Parkinson and eight control subjects. The reach was of either 15, 27.5 or 40 cm. The grasp was either of a small (0.7 cm) or a large diameter (8 cm) dowel. When comparing Parkinson to control subjects, no differences were found in the regulation of movement parameters according to changes in object distance or size. However, for Parkinson's disease patients the onset of the manipulation component was delayed with respect to the onset of the transport component. It is proposed that this reflects a deficit in the simultaneous or sequential implementation of different segments of a complex movement.

A kinematic study of the reach to grasp movement in a subject with hemiParkinson's disease.

The kinematic organization of a reach to grasp movement in a left hemiParkinson subject is compared to that of a control subject. Subjects used the right and left limbs to reach 15, 27 or 40 cm for the grasp of cylinders of 0.7 or 8 cm diameter. In general, the kinematics of the affected limb of the hemiParkinson subject differed from that of the unaffected limb. However, for both arms the hemiParkinson subject showed a delay in the onset of the manipulation component. The subtle dysfunction in the activation of near-simultaneous or sequential movements is thus bilateral, despite unilateral clinical symptomatology.

Perturbation of the grasp component of a prehension movement in a subject with hemiParkinson's disease.

The response to perturbation of the manipulation component during prehension was assessed for both hands of a hemiParkinson and of a Control subject. With perturbed trials, the hemiParkinson showed the same pattern as the Control: a reorganization of kinematic parameters and no increase of movement time. However, for both limbs of the hemiParkinson subject there was a transition phase from precision grip to whole hand prehension--this was more pronounced for the affected limb. The manipulation component did not show a delay of activation [2]. Thus the global dysfunction in the performance of sequential movement patterns was related to aspects of task predictability.

The reach-to-grasp movement in Parkinson's disease before and after dopaminergic medication.

The aim of the present study was to assess the effects of dopaminergic medication on the organisation of the reach-to-grasp movement in Parkinson's disease. A three-dimensional kinematic system (ELITE, B/T/S Italy) was used to record reach-to-grasp movements to objects of either small (0.7 cm) or large (8 cm) diameter placed at a reaching distance of either 20 or 30 cm. Vision of the reaching limb and target was also manipulated. Parkinson's disease participants (N = 14) were assessed in 'OFF' (12 h without medication) and 'ON' (1-2 h post-administration of medication) states. In the 'ON' state, movement duration and the time spent in arm deceleration were significantly less than in the 'OFF' state. The amplitudes of peak reaching velocity, acceleration and deceleration were all higher in the 'ON' than in the 'OFF' state. Further, in the 'ON' state, the acceleration profile no longer exhibited small irregular adjustments, the number of significant correlations between parameters measured from the transport and manipulation components was greater, and the movement was more direct in both the mediolateral horizontal and vertical planes. These results indicate that dopaminergic medication is of benefit in reducing bradykinesia and in fine-tuning kinematic parameterisation of a selected reach-to-grasp action.

Semantic category interference effects upon the reach-to-grasp movement.

In the present study the kinematics of the reach-to-grasp movement towards a target object in the presence of distractors was investigated. Three experiments were conducted. In the first experiment, there were three conditions, (a) the target alone, (b) the target presented with a distractor object that was semantically similar to the target and (c) the target presented with a distractor object that was semantically different from the target. The same conditions were repeated for the second experiment but the size of the distractors were also manipulated. For the third experiment the target was presented with a distractor object that was semantically different from the target but similar in shape. In the first experiment interference effects were observed in kinematic parameters of the grasp, but not for the reach component when the target and the distractor were semantically different. In the second and the third experiment, similar results were found. Results are discussed in terms of conflicting processing between objects pertaining to different semantic categories.

Kinematic analysis of the reach to grasp movement in Parkinson's and Huntington's disease subjects.

This experiment investigates the kinematic characteristics of the reach to grasp movement of Parkinson's and Huntington's disease subjects under two different experimental conditions. In the first condition subjects were required to perform the movement at a normal speed, while in the second condition they were required to perform the movement as fast as possible. Results showed that the kinematic parameterization of movement in Parkinson's disease subjects did not differ from that of age-matched control subjects for both the normal and the fast condition. However, the performances of Huntington's disease subjects appeared to be different when compared to the other two groups. Differences were mainly related to Huntington's disease patients' inability to properly define the temporal features of the movements.

Covert orienting and focusing of attention in children with attention deficit hyperactivity disorder.

Performance on the covert visuo-spatial attentional functions of orienting and focusing by a group of ADHD children (n = 20) was compared to that of age and sex-matched control children. In Experiment 1, responses were given to cued targets at valid and invalid locations. In Experiment 2, responses were given to targets presented in small, medium-sized or large visual field locations. For both experiments, the hypotheses that reaction times of ADHD children would be greater than those of control children and that performance would be asymmetrical, were supported. For Experiment 1, ADHD children showed bilaterally greater 'benefits' from having directed attention to the cued location and greater 'costs' in having to relocate the attentional focus than controls. In Experiment 2, the hypothesis that the function of focusing attention by ADHD children may show breakdown in the usual pattern of an increase in reaction time with focus area was partly supported by the finding of similar reaction times to targets presented in medium-sized and large regions of the left visual hemifield. These results have been interpreted as reflecting a stronger anchorage of attention by ADHD children upon a cued location and an inability to shift covert attention easily to an alternative location. The breakdown of the focusing function suggests adoption of similar time response sets across focus area size by the more compromised right hemisphere.

Influence of different types of grasping on the transport component of prehension movements.

The main aim of the present study was to clarify whether different types of grasping may affect the transport component of prehension movements. To this purpose two experiments were carried out. In the first experiment the kinematics of arm movements (transport and manipulation components) were studied in eight normal subjects instructed to reach and grasp different objects located either 20 or 30 cm from their hand. The objects employed required two different types of grip: prehension with the whole hand and prehension with the index finger and the thumb (precision grip). In the second experiment subjects were instructed to point to the same objects employed in the first experiment. This experiment served as a control for the precision requirements related to the object size. The results showed that, once the precision requirements were taken into account, the transport component remained unmodified with the different types of grip. The time course of the manipulation component and its temporal relations with the transport component changed with the type of grasping. The maximal hand aperture was reached earlier in the precision grip than in the whole hand prehension and the temporal coupling with the transport component was weaker in the former condition than in the latter. The data are interpreted as further evidence in favour of independence between the transport and the manipulation "channels".

Measuring time to awareness.

The timing of two simultaneous responses to one single visual event, namely the sudden subjective expansion of a real object occurring at the onset of a reaching movement, was measured in normal subjects. The motor response was represented by the earliest sign of correction in trajectory of the movement. The subjective report was represented by a vocal utterance that the subjects were instructed to emit when they became aware of the change in appearance of the object. The subjective report lagged the motor response by 150 ms. Control experiments ruled out a possible interference between the two responses. It is concluded that this temporal dissociation reflects a duality of neural pathways involved in processing object-related information.

How perceived object dimension influences prehension.

A kinematic study assessed the effects of the perceived dimensions of an object upon the patterning of a prehension movement involving that object. If an apple was perceived as two-dimensional, subjects utilized a large precision grip between the index finger and thumb. If the apple was perceived as three-dimensional, whole hand prehension involving all the digits was utilized. A visual perturbation from perceived two-dimensional to three-dimensional at movement onset resulted in a transition from the 2D precision grip pattern to the 3D whole hand prehension. These results suggest that visual mechanisms for interpreting the dimension of an object directly influence motor selection pathways, and do not necessarily access a three-dimensional central nervous system representation of the object.

Thumb invariance during prehension movement: effects of object orientation.

The aim of the present study was to examine the contribution of the thumb and index finger during the task of reaching to grasp a cylinder positioned at different orientations. To this end an axis was defined between a marker positioned on the subjects' wrist and the target. For each frame the perpendicular distances of the thumb and index finger from this axis were determined. The perpendicular distance was greater for the index finger than the thumb, confirming a relative stability of the thumb during natural prehension and supporting the notion of the thumb as a guide for the transport component of reaching. Further, index finger perpendicular distance was varied according to object orientation. When the object was positioned at an angle that requires hand pronation, the perpendicular distance for the index finger was the greatest. It is concluded that changes in the index finger distance are necessary to allow the thumb to maintain stability in order to provide appropriate movement guidance.

Modulation of unilateral neglect as a function of direction of object motion.

Unilateral neglect is a disorder involving difficulty in attending to the side of space contralesional to brain injury. Two recent experiments have shown that task-irrelevant background motion reduces neglect on line bisection tasks; however, task-relevant motion has not been assessed. We investigated the effect of task-relevant object motion on left neglect using a moving cube presented on a computer screen. Subjects responded to cued corners of the cube as it moved across the screen. Direction of cube motion had a significant impact on the magnitude of neglect. Responses to left hemispace targets appearing on a leftward moving cube were equal to patients' fastest responses. In contrast, responses to left hemispace targets appearing on a rightward moving cube were the slowest of all responses. These results demonstrate that contralesional object motion is capable of normalising neglect patients' detection of contralesional targets.

Upper limb movement differentiation according to taxonomic semantic category.

The size or shape of an object, its perceptual features, determine the patterning of an arm and hand action involving that object. Little is known about the role played by the taxonomic semantic attributes of an object for perceptuomotor processing. In this study we investigated whether the semantic relationship between two target stimuli influences the kinematics of a bilateral reach-to-grasp action. The results showed that reach-to-grasp movements preceding the action of putting living-thing pairs together were faster, and showed earlier settings of reach and grasp temporal parameters, than movements involving pairs of non-living things. It is hypothesized that this reflects the recruitment of different categorical perceptuomotor pathways.

Temporal coupling between transport and grasp components during prehension movements: effects of visual perturbation.

The temporal coupling between the transport and grasp components of prehension movements was investigated through two experiments. In Experiment 1, six normal subjects were required to reach and grasp each of three spheres located at three different distances (Blocked trials). In Experiment 2, a visual perturbation paradigm was used in which the location of the object to be reached and grasped could change at the beginning of arm movement (Perturbed trials). The same subjects participated in both experiments. Kinematics of wrist trajectory (transport component) and of distance between thumb and index finger (grasp component) were analyzed. The results of Experiment 1 showed that the two components could be temporally coupled during their time course. In Experiment 2, the visual perturbation affected both the components, but different times were required by each component to reorganize the movement towards the new target. These different times caused the decoupling of those events that appeared synchronized in Experiment 1. Finally, evidence was found to suggest that planning of grip formation takes into account not only the perceived characteristics of the object, but also the time planned by the transport component to reach the object.

The bilateral reach to grasp movement.

This study investigated the kinematic organization of bilateral reach to grasp movements. In Experiment 1 non-homologous bilateral movements were performed. One limb reached to grasp an object using whole hand prehension; the contralateral limb simultaneously reached to grasp an object using precision grip. Corresponding unilateral movements were assessed. Movement duration for each limb in the bilateral condition was similar. However, with earlier temporal settings for peak wrist acceleration and velocity, the limb performing precision grip showed a longer approach (deceleration) phase to the object. Unilateral precision grip movements showed a longer movement duration and deceleration phase than unilateral whole hand prehension movements. In Experiment 2 homologous bilateral movements were assessed. Both limbs performed either a reach and whole hand prehension or a reach and precision grip. Again the precision grip movements showed longer movement and deceleration times. Experiment 3 consisted of bilateral non-homologous pointing movements and a pointing movement with one limb while reaching to grasp with the contralateral limb. It was found that the earlier temporal settings of peak acceleration and velocity with the precision grip limb of the non-homologous bilateral task (Expt. 1) were largely due to the performance of distal grasping actions. It is concluded that a kinematic parameterization which is independent to each limb is evident for bilateral tasks which require functionally independent actions.

Does the type of prehension influence the kinematics of reaching?

Kinematic studies have indicated that when a subject reaches to grasp an object, the movement consists of two primary components: (a) a transport phase whereby the hand is brought towards the object and (b) a grip phase whereby the hand changes shape in anticipation of the grasp. Using a visual perturbation paradigm, we investigated the effect of different grip component strategies upon the transport phase. The distal strategy was determined by the size of the object to be grasped: for the small object (1.5 cm o.d.) subjects naturally adopted a precision grip between the index finger and thumb; for the large object (6 cm o.d.) subjects used a whole hand prehensile grip. During 20% of the reaching trials the perturbation was introduced by unexpectedly changing the object size. The results showed that corrections to the distal program in response to the perturbation were preceded by changes in the deceleration phase of the proximal component. The data supported previous findings of two visuo-motor channels for this prehensile movement but indicated that when unanticipated shifts of only the distal program are required, both channels show modifications.

Grasping a fruit: selection for action.

This study used a natural task, with no emphasis placed on speeded responses, to investigate unconscious information processing. Using the ELITE system, a kinematic analysis was performed of the upper limb reach-to-grasp movement. Nine experiments explored how the presence of distractors affects the transport and grasp component of this movement. Experiment 1 showed that the kinematics for grasping apples, mandarins, cherries, and bananas were measurably different. Experiments 2A-D, 3, and 4 showed that these kinematics were not affected by the presence of nearby distractor fruits of either the same or a different kind. In Experiment 5, interference effects became evident when participants were required to perform a subsidiary task involving the distractor (counting the number of times a laterally placed fruit was illuminated). Experiment 6, requiring both grasping a target fruit and counting the number of times that this fruit was illuminated, revealed no interference effects. Taken together, these results suggest that selection for action does not involve substantial passive processing of distractors. However, dual-action processing of simultaneously presented objects does appear to involve automatic processing of even the task-irrelevant properties of the distractor.