Biomedical subjects

F Doricchi

Publications and source records attributed to F Doricchi.

12 recordsLinked to original sources

PubMed1998

Seeing only the right half of the forest but cutting down all the trees?

Unilateral neglect following damage to the right hemisphere of the brain can be characterized by failure of the global attentional mechanisms of the right hemisphere to direct the local detail processors of the left hemisphere towards the contralesional left hemispace. This is suggested by patients who recognize the global form of the left side of shapes (the forest) but fail to cancel out its local details (the trees). Here we report the opposite behavioural dissociation in a patient (Q.M.) with damage to the right hemisphere of the brain. Q.M. detected local details (such as the tail of a dog) on the left or right side of visual shapes, regardless of whether these details belonged to predefined target shapes (a dog in this case) or to distractor shapes differing on the opposite side (a dog with a swan's neck and head, for example). Psychological testing showed an abnormal tendency of this patient to respond to local features, but perfect accuracy in interpreting global features when the local features could not interfere in global processing. The results indicate that the left hemisphere can integrate multiple local features simultaneously but loses global awareness as soon as local features individually compete for response selection. However, awareness of the whole is not necessary for the sequential processing of the parts.

Attention↗

PubMed1997

Neural control of fast-regular saccades and antisaccades: an investigation using positron emission tomography.

Regional cerebral blood flow changes related to the performance of two oculomotor tasks and a central fixation task were compared in ten healthy human subjects. The tasks were: (a) performance of fast-regular saccades; (b) performance of voluntary antisaccades away from a peripheral cue; (c) passive maintenance of central visual fixation in the presence of irrelevant peripheral stimulation. The saccadic task was associated with a relative increase in activity in a number of occipitotemporal areas. Compared with both the fixation and the saccadic task, the performance of antisaccades activated a set of areas including: the superior and inferior parietal lobules, the precentral and prefrontal cortex, the cingulate cortex, and the supplementary motor area. The results of the present study suggest that: (a) compared with self-determined saccadic responses the performance of fast regular, reflexive saccades produces a limited activation of the frontal eye fields; (b) in the antisaccadic task the inferior parietal lobes subserve operations of sensory-motor integration dealing with attentional disengagement from the initial peripheral cue (appearing at an invalid spatial location) and with the recomputation of the antisaccadic vector on the basis of the wrong (e.g., spatially opposite) information provided by the same cue.

Adult↗

PubMed1997

Gravitational inputs modulate visuospatial neglect.

Right brain-damaged patients with left visuospatial neglect were required to bisect a line placed in front of them in two different body positions (upright and supine) and two different light conditions (light and dark). The neglect patients, unlike right brain-damaged patients without neglect, strongly reduced their rightward directional error in the supine compared with the upright position. No systematic changes were produced by the light-dark manipulation. The present result cannot be explained with an attentional interpretation of hemispatial neglect. We suggest that the present data provide further evidence that hemineglect is the consequence of a mismatch between different afferent information integrated into an egocentric space representation. According to this model, the presence of a lateralized brain lesion produces asymmetries in some intermediate spatial representations (eye-head, head-trunk, body-environment) but not in the retinotopic one. Any experimental manipulation that reduces the asymmetry of the intermediate representation such as the reduction of gravitational inputs may improve the dynamic integration of the egocentric coordinates.

Aged↗

PubMed1996

Neglect for low luminance contrast stimuli but not for high colour contrast stimuli: a behavioural and electrophysiological case study.

We describe a patient with a right hemisphere lesion involving the frontal lobe, the post-central gyrus and the superior parietal lobule. Behavioural testing demonstrated severe left unilateral neglect to low luminance contrast stimuli, but not to high colour contrast stimuli. Evoked potentials to low contrast luminance gratings presented in the left hemifield were not reliable. However, equiluminant coloured gratings presented in the same hemifield evoked reliable electrophysiological responses, although longer in latency than those evoked in the right hemifield. These findings suggest that the patient has severe damage of the high contrast sensitivity magnocellular pathway in the right hemisphere, with minor involvement of the parvocellular pathway.

Brain Damage, Chronic↗

PubMed1996

Asymmetry of rapid eye movements in chronic unilateral neglect does not change with behavioral improvement induced by rehabilitation treatment.

A strong reduction of leftward rapid eye movements (REMs) during REM sleep was recently documented in patients with severe and chronic left unilateral neglect. The aim of the present research was to study the stability of the unilateral suppression of REMs before and after a rehabilitative treatment for neglect disorders. Six right-brain-damaged patients were tested for neglect at the beginning and at the end of a 2 month cognitive rehabilitation treatment. REMs were recorded during 1 night of undisturbed sleep before and after the training. Five out of 6 patients improved considerably their ability to attend the previously neglected left hemispace; in all patients REM asymmetry remained unchanged. The lack of relationship between the improvement of the neglect disorder and the persistence of REM asymmetry suggests that the sensorimotor mechanisms activated by rehabilitation are different from those involved in the production of REMs. It is proposed that: (a) the directional vectors of REMs are computed on the basis of the exclusive or predominant endogenous activation of the central attentional mechanisms related to vestibular input; (b) the presence of rightward and leftward saccades and the positive effects of the rehabilitation treatment are functionally linked to attentional oculomotor mechanisms that are not active in REM sleep.

Aged↗

PubMed1996

Attentional functions in multiple system atrophy and Parkinson's disease.

OBJECTIVE: To assess cognitive performances of patients with striatonigral degeneration type multiple system atrophy compared with those of patients with Parkinson's disease. METHODS: The cognitive performances of a group of patients with multiple system atrophy of the striatonigral type were compared with those of matched patients with Parkinson's disease and controls, using tests sensitive to frontal lobe dysfunction. RESULTS: The multiple system atrophy group, when compared with the Parkinson's disease group, showed significant deficits in attention tasks, particularly in the Stroop test. CONCLUSION: There was a consistently greater impairment in attention resources in patients with multiple system atrophy than in patients with Parkinson's disease.

Aged↗

PubMed1995

Gravity and hemineglect.

Spatial cognition requires the integration of visual inputs with proprioceptive and vestibular information about the position of the eye, the head and the body. All these sources are used by the brain to produce multiple higher-order (e.g. egocentric) representations of space, subserving accurate spatial behaviour. Such spatial representations are disrupted by unilateral cerebral damage producing neglect in the contralateral side of space. In eight brain-damaged patients with left unilateral neglect the manipulation of gravitational-otolithic information, obtained by placing patients in a supine position, produced a significant reduction of the rightward directional error in the line bisection task in all cases. This finding suggests that, in patients with neglect, gravitational information is processed in a non-symmetrical fashion, with a rightward bias towards the side of the lesion. This is the first study showing that manipulation of gravitational input affects neuropsychological disorders of visuo-spatial processing.

Aged↗

PubMed1995

Amplitude and speed change of the optokinetic response in patients with and without neglect.

The present study quantitatively investigated the slow and quick phases of optokinetic nystagmus (OKN) in four groups of patients: right unilateral brain-damaged patients with neglect, left and right patients without neglect or hemianopia and patients with left or right retrogeniculate lesions and lateral homonymous hemianopia. Our results indicate that only neglect patients show a perturbation of both components of OKN. A comparison among MRI images of different patients shows that a region involving area 37 and adjacent areas 39 and 19, was impaired in all patients with neglect, but not in any other patient with either right or left lesions.

Adolescent↗

PubMed1995

Generation of skeletal and multipart mental visual images in the cerebral hemispheres: a study in normal subjects.

In a series of three experiments the hemispheric lateralization of structures generating the details and the holistic properties of mental images was investigated in three different samples of normal right-handed subjects. In the first experiment the left hemisphere was faster in discriminating at an imagery level whether animals had short or long tails. No hemispheric dominance was found when the imagery task required the discrimination of the holistic features of objects and a decision of whether they were taller than wider, or vice versa. In the second experiment no hemispheric dominance was found when the same tasks had to be performed perceptually. In the third experiment no hemispheric dominance was found in the speed of lexical recognition of the names that in the first experiment elicited the generation of multipart and skeletal mental images, although the left hemisphere was generally more accurate. These findings provide support to the hypothesis advanced by Kosslyn that multipart mental images are generated by the left hemisphere and skeletal images by both hemispheres. Results are discussed both in terms of Kosslyn's computational theory of imagery generation and in terms of theories advanced by other authors.

Adolescent↗

PubMed1993

Disturbances of the rapid eye movements (REMs) of REM sleep in patients with unilateral attentional neglect: clue for the understanding of the functional meaning of REMs.

Horizontal saccades during wakefulness and horizontal rapid eye movements (REMs) during REM sleep were recorded in 6 unilateral brain damaged patients suffering from attentional neglect and 6 unilateral brain damaged control patients. During REM sleep, patients with neglect showed a nearly total suppression of REMs directed away from the side of the lesion; controls had a significantly milder frequency reduction of the same movements. In all patients the frequency reduction of REMs contralateral to the lesion equally affected isolated REMs (i.e., REMs preceded by intervals of oculomotor quiescence longer than 2 sec) and REM bursts (i.e., REMs preceded by intervals shorter than 2 sec). During voluntary inspection in waking, saccades directed ipsilaterally and contralaterally to the lesion were present in both groups of patients, although patients with neglect confined their inspection to the hemispace ipsilateral to the lesion. Results are discussed in terms of their implications for the understanding of the neurophysiological basis of REM sleep oculomotor activity and dream production, as well as for the neurophysiopathological basis of the neglect syndrome. It is proposed that REMs are functionally equivalent to waking reflex orienting saccades generated by a neural network including the relevant modulatory action of the parietal lobes and the superior colliculi.

Aged↗

PubMed1991

Disappearance of leftward rapid eye movements during sleep in left visual hemi-inattention.

Contrasting hypotheses have been proposed about the functional equivalence between waking saccades and REMs. Patients with left visual hemi-inattention showed dissociation between the direction of waking saccades and that of REMs. REMs directed toward the left were virtually absent, while waking inspective saccades directed in both lateral directions were present, but confined to the right hemispace. It is concluded that: a) the cortical areas regulating attention are relevant in the production of REMs; b) two separate attentional mechanisms have to be considered in relation to the hemi-inattentive syndrome, one is involved in the cognitive control of visual exploration and plays little or no role in the modulation of REMs, the other deals with REMs during sleep and with reflex-like orienting responses to peripheral stimuli during waking.

Aged↗

PubMedDate not supplied

Patterns of hemispheric lateralization in dream recallers and non-dream recallers.

Eighteen right handed females reporting 6 or more dreams per week on a home dream and sleep diary (Dream Recallers: DR), and 11 reporting 1 or 0 dreams per week (Non Dream Recallers: NDR) drawn from a sample of 233 college students, were individually tested on two tasks assessing the hemispheric lateralization of visuo-constructive and verbal-semantic functions. NDR showed a significant degree of hemispheric asymmetry of both visuo-constructive (right asymmetry of both visuo-constructive (right hemisphere advantage) and semantic (left hemisphere advantage) functions. DR showed no hemispheric advantage on both tasks. The two groups of subjects did not differ in mean daily amount of sleep time. In keeping with previous studies showing that NDR have an imbalance of interhemispheric activation upon REM awakenings, results from the present research suggest that DR and NDR can be characterized by a different pattern of hemispheric lateralization of cognitive skills. This finding may stimulate further research aimed at evaluating both the possible existence of differences in the lateralization of functions not considered in this study and the concomitance of REM sleep dependent differences in balance of hemispheric functioning.

Cognition↗