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PubMed2006

The role of the posterior parietal lobe in prism adaptation: Failure to adapt to optical prisms in a patient with bilateral damage to posterior parietal cortex.

We studied a patient (J.J.) with bilateral damage to those regions of the posterior parietal cortex (PPC) thought to be involved in prism adaptation. We demonstrated, for the first time in a parietal patient, that J.J. was unable to adapt to the visual perturbation induced by the optical prisms with either hand within four times the number of trials required by healthy adult subjects. We offer a novel account for the role of the PPC in prism adaptation: that the reach direction to the veridical target location specified in extrinsic limb-based coordinates must be de-coupled from the gaze direction to the perceived target location specified by intrinsic oculocentric coordinates in order to produce spatially accurate movements. This spatial discrepancy between gaze direction and reach direction may provide the necessary training signal required by the cerebellum to update the current internal model used to maintain spatial congruency between visual and proprioceptive maps of peripersonal space. The hypothesis is discussed in relation to recent disconnectionist accounts of optic ataxia.

Adaptation, Physiological↗
PubMed1978

Inaccurate reaching associated with a superior parietal lobe tumor.

A man with a tumor in the right superior parietal lobule had difficulty reaching for visualized objects. There were no significant deficits in visual sensation, visual attention, somatosensory function, elementary motility, praxis, or visuospatial performance. If allowed to visually fixate the target before reaching, he misreached only with his left arm and only when he was not allowed to observe the reaching limb. If he was required to maintain central visual fixation while reaching into his peripheral visual fields, his left arm misreached into both visual hemifields but his right arm misreached only into the left visual hemifield. These results demonstrate abnormalities, referable to both the contralateral arm and the contralateral visual field, that can neither be reduced to elementary disturbances of visual or somatosensory function nor to an elementary disturbance of motility. This pattern of misreaching has not been previously reported in human subjects or in experimental animals, but this may be attributable to differences of methodology. The misreaching observed in this patient may correspond to loss of posterior parietal neurons serving a supramodal integrative function.

Aged↗
PubMed1978

Mechanisms of neural integration in the parietal lobe for visual attention.

The impulse discharges of neurons in the inferior parietal association cortex (area 7) were studied in the alert, behaving rhesus monkey, trained to fixate and follow visual targets. Four classes of cells related to visual or visuomotor function were found. Cells of one of these are sensitive to visual stimuli and have large, contralateral receptive fields with maximal sensitivity in the far temporal quadrants. Cells of the other three classes are related to visuomotor functions: visual fixation, tracking, and saccades. They are neither sensory nor motor in the usual sense for they are activated only by interested fixation of gaze or tracking, or before visually evoked saccadic eye movements. They are not activated during the spontaneous saccades and fixations that the monkey makes while casually exploring his environment. It is hypothesized that the light-sensitive neurons provide the visual input to the visuomotor cells that, in turn, produce a command signal for the direction of visual attention and for shifting the focus of attention from one target to another.

Animals↗
PubMed1987

Is the hemispatial deficit produced by right parietal lobe damage associated with retinal or gravitational coordinates?

The hypothesis that right posterior parietal lesions cause two attentional deficits, namely, a reduced reactivity to stimuli in the left visual field (LVF), and a reduced reactivity to any stimulus which occupies a relative left position, was tested in 8 patients with an extinction syndrome. In Experiments 1 and 2 the first hypothesis was tested by measuring reaction times (RTs) to visual stimuli presented in the LVF and in the RVF, whereas the second hypothesis was tested by measuring RTs to stimuli totally positioned in the LVF, and in the RVF. The results showed that RTs to stimuli which occupied a relative left position were longer than RTs to stimuli which occupied a relative right position independent of the visual field stimulated and RTs to LVF stimuli were longer than RTs to RVF stimuli. Experiment 3 was designed to examine whether the attentional deficit associated with right parietal damage was mostly related to the use of gravitational rather than to retinal coordinates. In this experiment the patients tilted the head either to the left or the right by 90 deg and they responded to two stimuli displayed above and on either side of a fixation mark. The results showed that the difficulty in attending to the left was related both to the gravitational and the retinal frames of reference.

Aged↗
PubMed1994

Visually induced central pain and arm withdrawal after right parietal lobe infarction.

A 46 year old man with ischaemic infarction of the right parietal cortex had left hemianaesthesia when his eyes were closed. With eyes open, visual stimuli induced withdrawal of the arm and a burning pain in the numb side of the body. Visually induced central pain is a new clinical finding and may be related to damage of cells with anticipatory inhibitory function in the parietal association cortex.

Arm↗
PubMed1989

Distribution of cat-301 immunoreactivity in the frontal and parietal lobes of the macaque monkey.

The distribution of the monoclonal antibody Cat-301 was examined in the frontal and parietal cortex of macaque monkeys. In both regions the distribution was uniform within cytoarchitecturally defined areas (or subareas) but varied between them. In all areas, Cat-301 labeled the soma and proximal dendrites of a restricted population of neurons. In the frontal lobe, Cat-301-positive neurons were intensely immunoreactive and present in large numbers in the motor cortex (area 4), premotor cortex (area 6, excluding its lower ventral part), the supplementary motor area (SMA), and the caudal prefrontal cortex (areas 8a, 8b and 45). In the parietal lobe, large numbers of intensely immunoreactive neurons were evident in the post-central gyrus (areas 1 and 2), the superior parietal lobule (PE/5), and the dorsal bank (PEa), fundus (IPd), and deep half of the ventral bank (POa(i] of the intraparietal sulcus (IPS). Two major patterns of laminar distribution were evident. In motor, supplementary motor, premotor (excluding the lower part of its ventral division), and the caudal prefrontal cortex (Walker's areas 8a, 8b and 45), and throughout the parietal cortex (with the exception of area 3), Cat-301-positive neurons were concentrated in the lower part of layer III and in layer V. The laminar positions of labeled cells in these areas were remarkably constant, as were the proportions of labeled neurons that had pyramidal and nonpyramidal morphologies (means of 30.2% and 69.8%, respectively). In contrast, in prefrontal areas 9, 10, 11, 12, 13, 14, and 46, in the cingulate cortex (areas 23, 24 and 25), and in the lower part of the ventral premotor cortex, Cat-301-positive neurons were spread diffusely across layers II to VI and a mean of 3.6% of the labeled neurons were pyramidal while 96.4% were nonpyramidal. Area 3 was unique among frontal and parietal areas, in that the labeled neurons in this area were concentrated in layers IV and VI. The areas in the frontal lobe which were heavily labeled are thought to be involved in the control of somatic (areas 4 and 6) and ocular (areas 8 and 45) movements. Those in parietal cortex may be classified as areas with somatosensory functions (1, 2, PE/5, and PEa) and areas which may participate in the analysis of visual motion (Pandya and Seltzer's IPd and POa(i), which contain Maunsell and Van Essen's VIP). The parietal somatosensory areas are connected to frontal areas with somatic motor functions, while POa(i) is interconnected with the frontal eye fields (8a and 45).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗