Functional organization of human posterior parietal cortex: grasping- and reaching-related activations relative to topographically organized cortex.

The act of reaching to grasp an object requires the coordination between transporting the arm and shaping the hand. Neurophysiological, neuroimaging, neuroanatomic, and neuropsychological studies in macaque monkeys and humans suggest that the neural networks underlying grasping and reaching acts are at least partially separable within the posterior parietal cortex (PPC). To better understand how these neural networks have evolved in primates, we characterized the relationship between grasping- and reaching-related responses and topographically organized areas of the human intraparietal sulcus (IPS) using functional MRI.

Multisensory parietal cortex contributes to visual enhancement of touch in humans: A single-pulse TMS study.

We used transcranial magnetic stimulation (TMS) to investigate how the visual context provided by viewing one's own body influences somatosensory processing. In the visual enhancement of touch (VET) effect, viewing the body enhances tactile acuity relative to viewing a nonbody object. Single-pulse TMS was delivered over anterior intraparietal sulcus (aIPS), which is crucial for integrating visual and somatosensory information related to the body, during the interval between a brief glimpse of the arm, or an object, and tactile stimulation.

The functional neuroanatomy of object agnosia: a case study.

Cortical reorganization of visual and object representations following neural injury was examined using fMRI and behavioral investigations. We probed the visual responsivity of the ventral visual cortex of an agnosic patient who was impaired at object recognition following a lesion to the right lateral fusiform gyrus. In both hemispheres, retinotopic mapping revealed typical topographic organization and visual activation of early visual cortex.

Mechanisms of spatial attention control in frontal and parietal cortex.

Theories of spatial attentional control have been largely based upon studies of patients suffering from visuospatial neglect, resulting from circumscribed lesions of frontal and posterior parietal cortex. In the intact brain, the control of spatial attention has been related to a distributed frontoparietal attention network. Little is known about the nature of the control mechanisms exerted by this network.

I know where you'll look: an fMRI study of oculomotor intention and a change of motor plan.

Background: Electrophysiological studies in monkeys showed that the intention to perform a saccade and the covert change in motor plan are reflected in the neural activity of the posterior parietal cortex (PPC).

Methods: To investigate whether such covert intentional processes are demonstrable in humans as well we used event related functional MRI. Subjects were instructed to fixate a central target, which changed its color in order to indicate the direction of a subsequent saccade.

Representation of eye movements and stimulus motion in topographically organized areas of human posterior parietal cortex.

Recent imaging studies have shown that the human posterior parietal cortex (PPC) contains four topographically organized areas along the intraparietal sulcus (IPS1-IPS4). Using a memory-guided saccade paradigm, we confirmed the locations and retinotopic organization of IPS1-IPS4 and identified two additional areas, IPS5 and superior parietal lobule 1 (SPL1). IPS5 is located at the intersection of the intraparietal and postcentral sulcus; SPL1 branches off the IPS and extends into the superior parietal lobule.

Two hierarchically organized neural systems for object information in human visual cortex.

The primate visual system is broadly organized into two segregated processing pathways, a ventral stream for object vision and a dorsal stream for space vision. Here, evidence from functional brain imaging in humans demonstrates that object representations are not confined to the ventral pathway, but can also be found in several areas along the dorsal pathway. In both streams, areas at intermediate processing stages in extrastriate cortex (V4, V3A, MT and V7) showed object-selective but viewpoint- and size-specific responses.

Topographic maps in human frontal cortex revealed in memory-guided saccade and spatial working-memory tasks.

We used fMRI at 3 Tesla and improved spatial resolution (2 x 2 x 2 mm(3)) to investigate topographic organization in human frontal cortex using memory-guided response tasks performed at 8 or 12 peripheral locations arranged clockwise around a central fixation point. The tasks required the location of a peripheral target to be remembered for several seconds after which the subjects either made a saccade to the remembered location (memory-guided saccade task) or judged whether a test stimulus appeared in the same or a slightly different location by button press (spatial working-memory task). With these tasks, we found two topographic maps in each hemisphere, one in the superior branch of precentral cortex and caudalmost part of the superior frontal sulcus, in the region of the human frontal eye field, and a second in the inferior branch of precentral cortex and caudalmost part of the inferior frontal sulcus, both of which greatly overlapped with activations evoked by visually guided saccades.

An fMRI study of optokinetic nystagmus and smooth-pursuit eye movements in humans.

Both optokinetic nystagmus (OKN) and smooth-pursuit eye movements (SPEM) are subclasses of so-called slow eye movements. However, optokinetic responses are reflexive whereas smooth pursuit requires the voluntary tracking of a moving target. We used functional magnetic resonance imaging (fMRI) to determine the neural basis of OKN and SPEM, and to uncover whether the two underlying neural systems overlap or are independent at the cortical level.

The encoding of saccadic eye movements within human posterior parietal cortex.

Over the last few years, several functionally distinct subregions of the posterior parietal cortex (PPC) have been shown to subserve oculomotor control. Since these areas seem to overlap with regions whose activation is related to attention, we used functional magnetic resonance imaging to compare the cerebral activation pattern evoked by eye movements with different attentional loads, i.e.