SUMMARY1. In four Java monkeys (Macaca fascicularis) 152 vestibular neurones were recorded in the parietal cortex located in the upper bank of the lateral sulcus near the posterior end of the insula. We called this region parieto-insular vestibular cortex (PIVC). PIVC extends about 6-8 mm in the anterior-posterior direction from the posterior part of the insula into the retroinsular region (stereotaxic co-ordinates: anterior 4-12 mm, lateral 16-19 mm and vertical 3-6 mm).2. About two-thirds of the neurones recorded from this region responded to vestibular stimuli; the non-vestibular neurones responded predominantly to somatosensory stimulation of the neck and shoulder region. The PIVC area is a polysensory field, since almost all vestibular neurones were also activated by somatosensory and visual stimuli. Large-field optokinetic stimulation was the most effective visual stimulus.3. With vestibular stimuli, responses to angular acceleration were dominant; steady tilt in darkness rarely led to any change in neuronal spontaneous activity. Of sixty-four neurones tested by rotation in more than one plane, fifty-four responded to excitation of semicircular canal receptors aroused by rotation in more than one of the three experimental planes (roll, yaw, pitch 0. -J. GR USSER, M. PA USE AND U. SCHREITER rotational planes. For different units the relative sensitivity to rotation in each of the three planes also differed. We concluded from this observation that different PIVC units had different optimum sensitivity planes for rotation with respect to the head co-ordinates, whereby all possible planes are represented.

1. One hundred and fifty-two vestibularly activated neurones were recorded in the parieto-insular vestibular cortex (PIVC) of four awake Java monkeys (Macaca fascicularis): sixty-two were tested systematically with visual stimulation and seventy-nine were tested with various somatosensory stimuli. With very few exceptions all vestibular neurones tested responded to visual and somatosensory stimulation, therefore being classified as polymodal vestibular units. 2. A most effective stimulus for all fifty-eight visually activated PIVC units was movement of a large structured visual pattern in an optimal direction. From forty-four units responsive to a horizontally moving optokinetic striped drum, twenty-nine were activated with optokinetic movement in the opposite direction to the activating vestibular stimulus ('synergistic' response), thirteen were activated optokinetically and vestibularly in the same direction ('antagonistic' responses) and two were biphasic. The gain of the optokinetic response to sinusoidal stimulation (average 0.28 (impulses s-1) (deg s-1)-1 at 0.2 Hz, 56 deg amplitude) was in a range similar to that of the vestibular gain at low frequencies. At 1 Hz some units only showed weak optokinetic responses or none at all, but the vestibular response was still strong. 3. With different 'conflicting' or 'enhancing' combinations of optokinetic and vestibular stimulation no generalized type of interaction was observed, but the responses varied from nearly 'algebraic' summation to no discernible changes in the vestibular responses by additional optokinetic stimuli. With all visual-vestibular stimulus combinations the responses to the vestibular stimulus remained dominant. 4. The optokinetic preferred direction was not related to gravitational coordinates since the optokinetic responses were related to the head co-ordinates and remained constant with respect to the head co-ordinates at different angles of steady tilt. 5. Almost all PIVC units were activated by somatosensory stimulation, whereby mainly pressure and/or movement of neck and shoulders (bilateral) and movement of the arm joints elicited vigorous responses. Fewer neurones were activated by lightly touching shoulders/arms or neck, by vibration and/or pressure to the vertebrae, pelvis and legs. 6. A most effective somatosensory stimulus was sinewave rotation of the body with head stationary. The gain of this directionally selective neck receptor response was in the range of vestibular stimulation. Interaction of vestibular and neck receptor stimulation was either of a cancellation or facilitation type.(ABSTRACT TRUNCATED AT 400 WORDS)

1. Neurons activated by stimulation of the horizontal and/or vertical vestibular semicircular canals were recorded in the parietoinsular vestibular cortex in four awake Java monkeys (Macaca fascicularis) and three squirrel monkeys (Saimiri sciureus). Steady tilt in darkness or during illumination of a vertically striped cylinder or of the normal laboratory surroundings did not lead to a significant change in PIVC neuron activity. Thus vestibular input to this cortical region seems to be restricted to signals originating in the semicircular canal receptors. 2. Vestibular stimulation in the three main experimental planes (roll, yaw, and pitch) and in planes in between provided clear evidence that optimum activation can be found in planes that do not coincide with the planes of the semicircular canals but are distributed over all possible spatial planes through the head. 3. Definite evidence of clustering in subdivisions of PIVC of neurons responding to the same optimum rotation plane was obtained in squirrel monkeys and is also suggested to exist in PIVC of Java monkeys. 4. Nearly all neurons responding to vestibular stimulation were also activated by visual large-field movement (optokinetic stimulation). Responses to optokinetic stimuli were always at optimum when the direction of the movement pattern corresponded to the optimum vestibular plane. Two classes of visual-vestibular interaction were found: Synergistic neurons were those PIVC cells with the strongest response to visual movement stimulation in the opposite direction to that leading to a maximum response to vestibular stimulation. Antagonistic neurons had a response maximum when the visual stimulus was moved in the direction of optimum vestibular stimulation. 5. Most PIVC neurons responded to stimulation of the deep mechanoreceptors in the neck region. This input from the neck receptors was tested quantitatively only in the horizontal plane (trunk rotation with the head fixed in space or head rotation with the trunk fixed in space). It interacted with vestibular signals at the PIVC neurons either in an antagonistic or a synergistic manner, the latter meaning activation during rotation of the head in the same direction as that leading to activation induced by semicircular canal stimulation. 6. In addition to the direction-specific vestibular, visual, and neck receptor inputs, a rather complex somatosensory input to PIVC neurons exists, including responses to stimulation of mechanoreceptors of the skin, the muscles, and the joint receptors of legs and arms. Total body vibration also led to activation of some of the neurons.(ABSTRACT TRUNCATED AT 400 WORDS)

Omnipause neurons take part in the generation of saccadic eye movements. They lie around the midline in the caudal pontine reticular formation, in an area usually ascribed to the nucleus raphe pontis (rp). In this study of the monkey (Macaca fascicularis and M. mulatta), we describe four series of experiments aimed at establishing that omnipause neurons lie within a distinctive cytoarchitectonic entity, which we call the nucleus raphe interpositus (rip): (1) cytoarchitectural study, (2) recording-lesion experiments to establish in which cell group omnipause neurons lie, (3) cytochrome oxidase distribution in the omnipause region and neighboring structures, and (4) neuroanatomical tracing experiments to demonstrate afferents to the omnipause region. In the detailed cytoarchitectural study of the midline structures in the caudal pons and rostral medulla, a distinctive group of neurons (rip) adjoining the ventrocaudal border of rp and dorsal to the nucleus raphe magnus (rm) is described. The striking features of rip are the uniformly arranged, narrow row of the cells either side of the midline, and the extensive horizontally oriented dendritic trees of its neurons. The abducens rootlets (NVI) pass through the reticular formation at the same rostrocaudal level as rip and form a reliable landmark for its location. Cytochrome-oxidase-stained sections demonstrated additional differences between rip and adjacent cell groups: in rip the neurons and their extensive dendrites stained strongly, but not the surrounding neuropile, whereas in rp both the neurons and the neuropile stained darkly, so that individual neurons were difficult to see. Unlike rp, rip coincides with the location of omnipause neurons, and lesions marking the sites of individual omnipause units lay within its boundaries. Tritiated leucine was injected into superior colliculus (sc), which is known to have monosynaptic connections with omnipause neurons. Labelled axons and patterns of silver grains taken to indicate the presence of terminal branching were found in and around rip, but no significant labelling was seen in rp or rm. It is concluded that the omnipause neurons lie within the rip in the monkey. These functional and morphological differences between rip and the adjacent raphe nuclei are used to justify its characterization as an independent cell group in the monkey. In order to relate these findings to man, cytochrome oxidase experiments were carried out on the human brainstem, and the pattern of staining at the level of the abducens rootlets was correlated with the cytoarchitecture.(ABSTRACT TRUNCATED AT 400 WORDS)

Somatosensory and motor disturbances of hand function were examined in 9 patients with parietal lobe lesions. A quantitative score was used for the elaboration of sensorimotor profiles displaying the relative degree of functional impairment. In patients with anterior parietal lobe lesions somaesthesis was clearly more disturbed than motor function. Simple aspects of somaesthesis (surface sensibility, two-point discrimination, position sense) were disturbed to about the same degree as complex somatosensory (tactile recognition) tasks. On the other hand, patients with lesions of the posterior parietal lobe showed preferential impairment of complex somatosensory and motor functions (exploratory and manipulative finger movements). In 4 patients, analysis of motor behaviour by means of an optoelectronic system showed that reaching, formation of hand aperture and target acquisition were less disturbed than manipulative behaviour. Finger movement trajectories during dynamic digital palpation of objects were grossly deranged in the patients with posterior parietal damage. The temporal characteristics of the finger movements during active touch were completely destroyed. This leads to a breakdown of the finely tuned digital scanning process required for the sequential sampling of mechanoreceptive information. Remarkably, these patients could produce the exploratory finger movements imitatively. The motor disability of the parietal hand does not lie in the loss of the kinetic memory to perform these movements, but in the loss of their evocation by appropriate sensory stimuli. This deficit is not due to a lack of somatosensory information because that may be relatively well preserved. It is concluded that the motor disturbance in posterior parietal lobe disease lies essentially in the conception and execution of the spatiotemporal movement patterns necessary to bring those receptors into action which would normally provide the information about tactile objects. This illustrates the intricate mutual dependence of the spatiotemporal organization of receptor activation by movement and of the formation of movement trajectories on the basis of adequate sensory processing.