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The parietal cortex and saccade planning: lessons from human lesion studies.

Ptak R, Müri RM - Front Hum Neurosci (2013)

Bottom Line: The parietal cortex is a critical interface for attention and integration of multiple sensory signals that can be used for the implementation of motor plans.Many neurons in this region exhibit strong attention-, reach-, grasp- or saccade-related activity.However, these patients also show bilateral impairments of saccade initiation and control that are difficult to explain in the context of their lateralized deficits of visual attention.

View Article: PubMed Central - PubMed

Affiliation: Division of Neurorehabilitation, University Hospitals Geneva Geneva, Switzerland ; Laboratory of Cognitive Neurorehabilitation, Faculty of Medicine, University of Geneva Geneva, Switzerland ; Faculty of Psychology and Educational Sciences, University of Geneva Geneva, Switzerland.

ABSTRACT
The parietal cortex is a critical interface for attention and integration of multiple sensory signals that can be used for the implementation of motor plans. Many neurons in this region exhibit strong attention-, reach-, grasp- or saccade-related activity. Here, we review human lesion studies supporting the critical role of the parietal cortex in saccade planning. Studies of patients with unilateral parietal damage and spatial neglect reveal characteristic spatially lateralized deficits of saccade programming when multiple stimuli compete for attention. However, these patients also show bilateral impairments of saccade initiation and control that are difficult to explain in the context of their lateralized deficits of visual attention. These findings are reminiscent of the deficits of oculomotor control observed in patients with Bálint's syndrome consecutive to bilateral parietal damage. We propose that some oculomotor deficits following parietal damage are compatible with a decisive role of the parietal cortex in saccade planning under conditions of sensory competition, while other deficits reflect disinhibition of low-level structures of the oculomotor network in the absence of top-down parietal modulation.

No MeSH data available.


Related in: MedlinePlus

Patterns of visual exploration in simultanagnosia. (A) Portrait used by Yarbus (1967) when studying face exploration. (B) Scan-path of a healthy subject and (C) of a patient with simultanagnosia when exploring the picture shown in (A). (D) Scan-path and fixation-density plot from a patient with simultanagnosia and (E) a healthy subject exploring a clock-face [A and B: adapted from Yarbus (1967); C: adapted from Luria et al. (1963); D and E: adapted from Nyffeler et al. (2005)] with permission from Elsevier.
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Figure 4: Patterns of visual exploration in simultanagnosia. (A) Portrait used by Yarbus (1967) when studying face exploration. (B) Scan-path of a healthy subject and (C) of a patient with simultanagnosia when exploring the picture shown in (A). (D) Scan-path and fixation-density plot from a patient with simultanagnosia and (E) a healthy subject exploring a clock-face [A and B: adapted from Yarbus (1967); C: adapted from Luria et al. (1963); D and E: adapted from Nyffeler et al. (2005)] with permission from Elsevier.

Mentions: A much earlier eye tracking study using a method developed by Yarbus (1967) had already investigated visual scanning in a patient with simultanagnosia (Luria et al., 1963). The authors noted that the patient had normal fixation of an isolated light in the dark as well as normal smooth pursuit eye movements of a single target in regular motion. In contrast, eye movements were essentially random when the task required visual scanning, such as when the patient was asked to perform simple saccades between two stimuli or when observing the image of a face (Figure 4). Another patient examined by Girotti et al. (1982) also exhibited spatially disorganized eye movements and was only able to fixate a visual stimulus after repeated erratic eye movements. In contrast to Luria's patient however, their patient was also unable to follow visually a moving target and could not voluntarily generate saccades on verbal command, suggesting a generalized impairment of eye movement programming. The patient of Nyffeler et al. (2005) showed abnormal scanning of horizontally aligned line drawings and of the picture of a clock face (Figure 4). When asked to read the clock she inspected uninformative numbers irrespective of the position of the hands instead of fixating the clock hands and the corresponding numbers as control participants did. Two other simultanagnosic patients (Dalrymple et al., 2011, 2013) failed to fixate the informative eye regions in social scenes, while making many fixations on irrelevant stimuli.


The parietal cortex and saccade planning: lessons from human lesion studies.

Ptak R, Müri RM - Front Hum Neurosci (2013)

Patterns of visual exploration in simultanagnosia. (A) Portrait used by Yarbus (1967) when studying face exploration. (B) Scan-path of a healthy subject and (C) of a patient with simultanagnosia when exploring the picture shown in (A). (D) Scan-path and fixation-density plot from a patient with simultanagnosia and (E) a healthy subject exploring a clock-face [A and B: adapted from Yarbus (1967); C: adapted from Luria et al. (1963); D and E: adapted from Nyffeler et al. (2005)] with permission from Elsevier.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3675316&req=5

Figure 4: Patterns of visual exploration in simultanagnosia. (A) Portrait used by Yarbus (1967) when studying face exploration. (B) Scan-path of a healthy subject and (C) of a patient with simultanagnosia when exploring the picture shown in (A). (D) Scan-path and fixation-density plot from a patient with simultanagnosia and (E) a healthy subject exploring a clock-face [A and B: adapted from Yarbus (1967); C: adapted from Luria et al. (1963); D and E: adapted from Nyffeler et al. (2005)] with permission from Elsevier.
Mentions: A much earlier eye tracking study using a method developed by Yarbus (1967) had already investigated visual scanning in a patient with simultanagnosia (Luria et al., 1963). The authors noted that the patient had normal fixation of an isolated light in the dark as well as normal smooth pursuit eye movements of a single target in regular motion. In contrast, eye movements were essentially random when the task required visual scanning, such as when the patient was asked to perform simple saccades between two stimuli or when observing the image of a face (Figure 4). Another patient examined by Girotti et al. (1982) also exhibited spatially disorganized eye movements and was only able to fixate a visual stimulus after repeated erratic eye movements. In contrast to Luria's patient however, their patient was also unable to follow visually a moving target and could not voluntarily generate saccades on verbal command, suggesting a generalized impairment of eye movement programming. The patient of Nyffeler et al. (2005) showed abnormal scanning of horizontally aligned line drawings and of the picture of a clock face (Figure 4). When asked to read the clock she inspected uninformative numbers irrespective of the position of the hands instead of fixating the clock hands and the corresponding numbers as control participants did. Two other simultanagnosic patients (Dalrymple et al., 2011, 2013) failed to fixate the informative eye regions in social scenes, while making many fixations on irrelevant stimuli.

Bottom Line: The parietal cortex is a critical interface for attention and integration of multiple sensory signals that can be used for the implementation of motor plans.Many neurons in this region exhibit strong attention-, reach-, grasp- or saccade-related activity.However, these patients also show bilateral impairments of saccade initiation and control that are difficult to explain in the context of their lateralized deficits of visual attention.

View Article: PubMed Central - PubMed

Affiliation: Division of Neurorehabilitation, University Hospitals Geneva Geneva, Switzerland ; Laboratory of Cognitive Neurorehabilitation, Faculty of Medicine, University of Geneva Geneva, Switzerland ; Faculty of Psychology and Educational Sciences, University of Geneva Geneva, Switzerland.

ABSTRACT
The parietal cortex is a critical interface for attention and integration of multiple sensory signals that can be used for the implementation of motor plans. Many neurons in this region exhibit strong attention-, reach-, grasp- or saccade-related activity. Here, we review human lesion studies supporting the critical role of the parietal cortex in saccade planning. Studies of patients with unilateral parietal damage and spatial neglect reveal characteristic spatially lateralized deficits of saccade programming when multiple stimuli compete for attention. However, these patients also show bilateral impairments of saccade initiation and control that are difficult to explain in the context of their lateralized deficits of visual attention. These findings are reminiscent of the deficits of oculomotor control observed in patients with Bálint's syndrome consecutive to bilateral parietal damage. We propose that some oculomotor deficits following parietal damage are compatible with a decisive role of the parietal cortex in saccade planning under conditions of sensory competition, while other deficits reflect disinhibition of low-level structures of the oculomotor network in the absence of top-down parietal modulation.

No MeSH data available.


Related in: MedlinePlus