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Results for “Parietal Lobe”

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PubMed2000

Corticocortical connections of visual, sensorimotor, and multimodal processing areas in the parietal lobe of the macaque monkey.

We studied the corticocortical connections of architectonically defined areas of parietal and temporoparietal cortex, with emphasis on areas in the intraparietal sulcus (IPS) that are implicated in visual and somatosensory integration. Retrograde tracers were injected into selected areas of the IPS, superior temporal sulcus, and parietal lobule. The distribution of labeled cells was charted in relation to architectonically defined borders throughout the hemisphere and displayed on computer-generated three-dimensional reconstructions and on cortical flat maps. Injections centered in the ventral intraparietal area (VIP) revealed a complex pattern of inputs from numerous visual, somatosensory, motor, and polysensory areas, and from presumed vestibular- and auditory-related areas. Sensorimotor projections were predominantly from the upper body representations of at least six somatotopically organized areas. In contrast, injections centered in the neighboring ventral lateral intraparietal area (LIPv) revealed inputs mainly from extrastriate visual areas, consistent with previous studies. The pattern of inputs to LIPv largely overlapped those to zone MSTdp, a newly described subdivision of the medial superior temporal area. These results, in conjunction with those from injections into other parietal areas (7a, 7b, and anterior intraparietal area), support the fine-grained architectonic partitioning of cortical areas described in the preceding study. They also support and extend previous evidence for multiple distributed networks that are implicated in multimodal integration, especially with regard to area VIP.

Animals↗
PubMed1977

Parietal lobe mechanisms for directed visual attention.

1. Experiments were made on the cortex of the inferior parietal lobule in 10 hemispheres of six alert, behaving monkeys. The electrical signs of the impulse discharges of single cortical cells were recorded as the monkeys executed tasks requiring them to fixate stationary visual targets, track those which moved slowly, and to make saccadic movements to foveate those which suddenly jumped from one locus to another within the field of view. A total of 907 neurons of area 7 were identified in terms of their physiological properties, particularly the correlation of their activity with the oculomotor components of these behavioral acts of directed visual attention; 480 of these were located by cytoarchitectural layer. Most identifiable cells of area 7 are visuomotor neurons, in a special and conditional sense. Their discharge frequencies increase before and during those steady fixations and movements of the eyes which secure and maintain foveation of objects, but only if the visual targets engaged are linked by a strong motivational drive; in our experiments, one between thirst and the light whose dimming the animal has learned to detect for liquid reward. We have identified and studied three major classes of neurons in area 7. 2. The visual fixation neurons (57%) accelerate discharge synchronously with fixation of a visual object the animal desires. The incremented discharge continues until reward, but then declines abruptly even when there is no immediate shift of the line of gaze. Fixation neurons are relatively inactive during those casual fixations by which the animal insepcts the surrounding environment. Mist fixation neurons subtend gaze fields limited to one quadrant or half of the total gaze field. The sum of the gaze fields of the fixation neurons in one hemisphere is weighted moderately toward the contralateral side. Fixation cells also discharge during slow pursuit movements in any direction so long as the movement stays within the gaze field of the neuron under study. About 40% of fixation cells are suppressed before and during saccadic movements of the eyes to a new target within the gaze field of the fixation cell. Those suppressed are located preferentially in layer V of the cortex. Suppression is maximal for saccades directed contralaterally to the hemisphere under study. 3. Visual tracking neurons are active during oculomotor pursuit of slowly moving visual objects, not during steady fixations. They show a marked directional but no laterality relation, and are suppressed before and during a visually evoked saccade superimposed on the smooth pursuit movement. The rate of discharge is a flat function of tracking speed so that these cells do not appear to emit signals which specify the speed of smooth pursuit movements. 4. The saccade neurons are active before and during visually evoked saccadic movements of the eyes but not before spontaneous saccades, no matter whether made in light or near darkness. The discharge of saccade neurons leads the eye movement by as much as 150 ms (mean, 73 ms)...

Action Potentials↗
PubMed2006

Oculomotor functions of the parietal lobe: Effects of chronic lesions in humans.

This review summarises research in patients with chronic lesions of parietal oculomotor cortex and compares their oculomotor performance to patients with lesions of the frontal eye field (FEF). The observations identify the oculomotor functions for which these regions are indispensable, and explore dynamic interactions within cortical and subcortical networks for oculomotor control. The experiments examined endogenously generated saccades, saccades to visual targets, antisaccades, saccade choice and saccade remapping for inhibitory spatial tagging. The findings suggest that the key function of parietal oculomotor cortex is the computation of sensorimotor transformations, rather than the initiation of either voluntary or reflexive saccades. They also reveal the re-organisation of cortico-subcortical networks after brain injury, and provide insight into their dynamic interactions: FEF lesions result in disinhibition of reflexive saccades toward the contralesional field and an impairment of reflexive saccades toward the ipsilesional field; whereas parietal lesion result in the opposite pattern.

Chronic Disease↗
PubMed1983

Subcortical projections to the occipital and parietal lobes of the chimpanzee brain.

The subcortical sources of afferents to occipital and parietal cortex were studied in two chimpanzees with the aid of retrogradely transported horseradish peroxidase (HRP). In chimpanzee 1, HRP was injected into right cortical areas 17 and 18; chimpanzee 2 received HRP into right areas 17, 18, 19, and 39. The following subcortical structures were found to project to area 17 and/or area 18: locus coeruleus, dorsal raphe nucleus, nucleus annularis, nucleus centralis superior, pontine reticular formation, mesencephalic reticular formation, dorsal hypothalamus, lateral hypothalamus, nucleus basalis of Meynert, nucleus of the diagonal band of Broca, claustrum, nucleus basalis lateralis amygdalae, lateral geniculate nucleus, inferior pulvinar, lateral pulvinar, nucleus limitans, medial magnocellular part of the nucleus ventralis anterior, nucleus paracentralis, and nucleus centralis medialis thalami. Some of these structures may also project to area 19 and/or area 39. The following thalamic nuclei were found to project to area 19 and/or area 39 but not to areas 17 and 18: nucleus lateralis posterior, nucleus centralis lateralis, nucleus medialis dorsalis, nucleus ventralis lateralis, nucleus ventralis anterior nucleus lateralis dorsalis, and nucleus anterior ventralis. In several Instances, the HRP-labeled cells traversed specific nuclear borders, extending uninterruptedly from one classically defined nucleus into another. These results in the chimpanzee largely confirm data from a number of other mammalian taxa on the subcortical sources of afferents to the posterior cortex. Because of the close biological relationship between chimpanzee and man, we feel confident that such projections are also features of the human brain.

Amygdala↗
PubMed2004

Shift in sound localization induced by rTMS of the posterior parietal lobe.

Neuroimaging studies in human subjects and single-unit recordings in monkeys have suggested the primate posterior parietal cortex (PPC) to be involved in auditory space perception. Here we tested this hypothesis by combining repetitive focal transcranial magnetic stimulation (rTMS) of the right PPC with a task of pointing to free-field-sound stimuli. After a period of 15 min rTMS at 1Hz, subjects exhibited an overall signed error in pointing by 2.5 degrees, directed to the left and downward, with reference to a baseline condition with "sham rTMS". No effects of rTMS on the general precision of sound localization (unsigned errors) were found. Thus, low-frequency offline rTMS may have specifically affected neuronal circuits transforming auditory spatial coordinates in both azimuth and elevation. This is in accordance with the view that the PPC may represent a neural substrate of the perceptual stability in spatial hearing.

Acoustic Stimulation↗