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Visual pathways for object-oriented action and object recognition: functional anatomy with PET.

The purpose of this study was to identify the functional anatomy of the mechanisms involved in visually guided prehension and in object recognition in humans. The cerebral blood flow of seven subjects was investigated by positron emission tomography. Three conditions were performed using the same set of stimuli. In the 'grasping' condition, subjects were instructed to accurately grasp the objects. In the 'matching' condition, subjects were requested to compare the shape of the presented object with that of the previous one. In the 'pointing' condition (control), subjects pointed towards the objects. The comparison between grasping and pointing showed a regional cerebral blood flow (rCBF) increase in the anterior part of the inferior parietal cortex and part of the posterior parietal cortex. The comparison between grasping and matching showed an rCBF increase in the cerebellum, the left frontal cortex around the central sulcus, the mesial frontal cortex and the left inferior parietal cortex. Finally, the comparison between matching and pointing showed an rCBF increase in the right temporal cortex and the right posterior parietal cortex. Thus object-oriented action and object recognition activate a common posterior parietal area, suggesting that some kind of within-object spatial analysis was processed by this area whatever the goal of the task.

Adult↗
PubMed1984

Component specificity in albino VEP asymmetry: maturation of the visual pathway anomaly.

The existence of an isolated albino asymmetry component was investigated in the visual evoked potential (pattern appearance/disappearance response) of 96 albinos ranging in age from 3 months to 65 years. Misrouted optic pathway projections in albinism produce VEP asymmetry across the left and right occiput upon monocular whole field stimulation of a checkerboard pattern (element size, 55'). Our results indicate that the asymmetry which reflects the albino feature is contralateral and is restricted to an early period of the appearance response corresponding to the latency of the CI component. Further support for CI component specificity in albino asymmetry is provided by half-field stimulation in non-albino controls and by the results of a component maturation study in children under 6 years of age.

Age Factors↗
PubMed1990

Damage to the anterior visual pathway and brain parenchyma following external pituitary irradiation.

Three cases of damage to the optic nerves and chiasma following pituitary irradiation with Co60 teletherapy are described. All of them presented with progressive visual impairment months following irradiation and simulated recurrence of the tumour. CT scan was also not helpful in differentiating radionecrosis from tumour recurrence. On exploration the optic nerves and chiasma appeared discoloured and scarred. One case, who also had diffuse radionecrosis of brain parenchyma, died. No satisfactory therapy is currently available for this grave complication but proper safeguards can prevent it.

Adult↗