Abstract
This study integrated functional connectivity measures using resting-state fMRI and behavioral data from a single-case observation of patient (PER) one year after right-hemispheric hemorrhage in the intraparietal sulcus and superior parietal lobule (IPS/SPL). PER showed no sign of clinical neglect. Her behavioral performance in the visuo-manual pointing task and in the letter discrimination task under conditions of endogenous and exogenous attentional cueing was compared between the left (affected) and right (unaffected/control) peripheral visual fields. The resting-state fMRI demonstrated an imbalance between the right and left hemispheric frontoparietal functional connectivity within the dorsal attentional and motor networks. Although the frontal and occipital cortices were not structurally damaged, specific fronto-occipital functional connectivity was imbalanced, which was strongly associated with the behavioral changes. First, the activity in the right frontal eye field showed weaker correlations with the activity in the right inferior occipital area compared to the correlation with the activity in the left inferior occipital area. This imbalanced fronto-occipital functional connectivity was accompanied by a specific impairment in endogenous covert attention in the left visual field. Second, the activity within M1 in both hemispheres showed weaker correlations with the activity of the right cuneus compared to the correlation with the activity in the left cuneus. The imbalanced fronto-occipital functional connectivity was associated with the impairment of the reaching movement of the left and right hands towards the left visual field (optic ataxia). Altogether, our results showed that a lesion to the posterior parietal cortex affects the relationship between distal regions underlying the sensorimotor and attentional abilities
Highlights
Covert attention facilitates the perception of peripheral visual field stimuli and relies on top-down modulation of areas by frontoparietal attentional networks within the occipitotemporal visual stream dedicated to object recognition
The ventral frontoparietal attentional network - (VAN) [9, 10] is restricted to the right hemisphere and includes two frontal regions, the medial frontal gyri (MFG) and the inferior frontal gyri (IFG), as well as a parietal region known as the supramarginal gyrus (SMG), which is a part of the temporoparietal junction (TPJ)
PER discriminated the left targets in the covert endogenous attention condition less accurately than the right targets; the discrimination accuracy for left targets was similar to chance levels (50%) while the discrimination accuracy for right targets was above chance levels
Summary
Covert attention facilitates the perception of peripheral visual field stimuli and relies on top-down modulation of areas by frontoparietal attentional networks within the occipitotemporal visual stream dedicated to object recognition. Clinical examination of patients with IPS/SPL lesions often reveals optic ataxia, a neurological deficit in which patients have no primary perceptual or motor deficits but present difficulties in responding to objects in the contralesional peripheral visual field [13,14,15,16,17,18,19,20], and in fast visuomotor transformations known to depend on interactions between the occipito-parietal region and the dorsal premotor and primary motor cortices (e.g., [21,22,23,24,25,26,27,28,29,30]). Close examination of patients with focal IPS/SPL lesions and without clinical neglect syndrome, for example, by using briefly flashed stimuli, sometimes reveals attentional difficulties in the form of sub-clinical visual detection and discrimination deficits that are specific to covert endogenous orienting in the contralesional peripheral visual field [31,32,33,34,35,36]
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