Acetylcholine dramatically increases prostanoid synthesis in piglet parietal cortex

We investigated effects of exogenous acetylcholine on prostanoid synthesis by parietal cortex in neonatal pigs. Cerebrospinal fluid (CSF) with no drug, and CSF containing acetylcholine at 10(-6) to 10(-3) M was injected under a 'closed' cranial window, and after 5 min the CSF was collected and analyzed by radioimmunoassay for prostaglandin (PG) E2, PGF2 alpha, PGD2, 6-keto-PGF1 alpha (the hydrolysis product of prostacyclin), and thromboxane (TX) B2 (the hydrolysis product of TXA2). PGE2 and PGF2 alpha were the predominant prostanoids in CSF under control conditions. Levels of all CSF prostanoids increased after topical application of acetylcholine, with the largest increases being for PGE2 and PGF2 alpha. During control conditions, levels were 1294 +/- 170 (mean +/- S.E.M.) pg/ml for PGE2 (n = 16), 1032 +/- 143 pg/ml for PGF2 alpha (n = 3), 659 +/- 92 pg/ml for 6-keto-PGF1 alpha (n = 15), 141 +/- 44 pg/ml for TXB2 (n = 12), and were below detectable levels for PGD2. Following application of 10(-3) M acetylcholine, levels were 34,535 +/- 5438 pg/ml for PGE2, 15,539 +/- 2772 pg/ml for PGF2 alpha, 2967 +/- 547 pg/ml for 6-keto-PGF1 alpha, 580 +/- 105 pg/ml for TXB2, and 556 +/- 221 pg/ml for PGD2. These results suggest that prostanoids could play a role in mediating effects of acetylcholine in the brain, or in modulating acetylcholine release via a negative feedback mechanism.     

Eicosanoid formation in the rat cerebral cortex

Despite the extensive literature on brain eicosanoids, no information is available on the cellular source of individual compounds in the mature organ and the relative contribution of different cell types to the total synthetic product. To address this problem, neurons and glia were isolated from the cerebral cortex of the adult rat by a process comprising, in order, trypsinization, selective sieving, differential centrifugation, and density gradient centrifugation. Enrichment of cells in the appropriate fractions was verified by morphological, immunocytochemical, and biochemical criteria. Both neuron- and glia-rich fractions retained synthetic activity throughout the period of incubation (max. 60 min). Among the eicosanoids examined, prostaglandin (PG) E₂ was the predominant compound, followed by leukotriene (LT) E₄ and thromboxane (TX) B₂, whereas LTC₄ occurred in minimal amounts. Although the rank order of eicosanoids did not vary with the cell type, absolute values of PGE₂ and TXB₂ were greater with neurons. PGE₂ synthesis was increased by supplementation of the medium with arachidonic acid (2.6 μM), whereas indomethacin (5.6 μM) had the opposite effect. Conversely, LT synthesis was not altered by arachidonic acid and was only marginally reduced by the 5-lipoxygenase inhibitor, U-60,257 (10 μM). Several agonists (12-O-tetradecanoyl-phorbol-13-acetate, TPA; Ca ionophore A23187; plateletactivating factor; endotoxin; recombinant IL-1) were tested on both neuron- and glia-rich fractions but none of them had an effect. We conclude that freshly isolated neurons and glia are viable insofar as the basal rate of eicosanoid synthesis is concerned. No qualitative difference was noted between the two cell types in the spectrum of products formed and the spectrum itself accorded with early data on the biosynthetic activity of the intact tissue in vivo. Our isolation procedure appears useful for the analysis of the cellular source of eicosanoids under resting conditions, although it cannot be applied to the study of the site and mode of action of activators.     

Social cognition in premotor and parietal cortex

Socially correct behavior requires constant observation of the social environment. Behavior that was appropriate a few seconds ago is not guaranteed to be appropriate now. The brain keeps the eyes focused on the current social space and constantly updates its internal representation of the environment and social context. Monitoring the behavior of others is essential for this updating. The neural systems involved in perceiving the actions of others have been explored extensively, but the detailed, quantitative character of the system at the single-cell level remains poorly understood. To address this question, we used the new technique of multidimensional recording to record neuronal activity in monkeys simultaneously from ventral premotor cortex (PM) and parietal cortex in the left hemisphere while they performed a food grab task. Motion-related (MR) response was shown by 35% (52/148) of PM neurons and 54% (94/174) of parietal neurons, meaning their activity increased in response to various combinations of arm motions made by self and/or other. Both areas showed robust lateralized preference to Self-Right action. When it came to recognizing the actions of the other monkey, PM-MR neurons showed the same kind of right-arm preference as self-action while parietal-MR neurons, in contrast, did not show arm preference. And while both areas discriminated self-action from other, a significantly larger proportion of PM-MR neurons did so. These results suggest that PM neurons provide information about an action's agent and effector as primitives of action cognition within the mirror neuron network,while parietal neurons represent social space and participate in the recognition of another agent's actions in relation to one's own actions within the parieto-prefrontal network.     

Spatially modulated touch responses in parietal cortex

Cortical neurons with low-threshold, cutaneous receptive fields on the fingers were recorded in areas 5 and 7b of the parietal lobe in two awake monkeys, trained in a visually guided reach task. 72% (81/113) of the cells responded when targets displayed on a videomonitor were actively touched. Of these, 20 neurons discharged preferentially when target contact was made on one side of the screen compared with the other. This spatial modulation of the cutaneous modality may have originated in neighboring joint-related neurons which were directionally selective.     

Action selectivity in parietal and temporal cortex

The sensory-action theory proposes that the neural substrates underlying action representations are related to a visuomotor action system encompassing the left ventral premotor cortex, the anterior intraparietal (AIP) and left posterior middle temporal gyrus (LPMT). Using fMRI, we demonstrate that semantic decisions on action, relative to non-action words, increased activation in the left AIP and LPMT irrespective of whether the words were presented in a written or spoken form. Left AIP and LPMT might thus play the role of amodal semantic regions that can be activated via auditory as well as visual input. Left AIP and LPMT did not distinguish between different types of actions such as hand actions and whole body movements, although a right STS region responded selectively to whole body movements.     

Interhemispheric interzonal connections in the parietal cortex

In acute experiments on cats immobilized by tubarine transcallosal responses (TCRs) to the stimulation of the visual or auditory cortex of the opposite hemisphere were investigated in the parietal associative region. It was found that interzonal heterotopical TCRs could be recorded along the entire surface of the parietal cortex and were in two forms: positive-negative or negative-positive. Positive-negative evoked potentials (EPs) had greater latent periods. Negative-positive TCRs disappeared after the corpus callosum section or after the section of intracortical pathways on the side of recording and/or stimulation. EPs with initial positivity changed insignificantly as a result of these operations. Interzonal TCRs were characterized by the presence of interhemispheric asymmetry. The amplitude of early components in visual-parietal EPs of any configuration appeared to be greater in the right hemisphere. These responses also had a greater latent period. According to the magnitude of the late positive wave in visual-parietal TCRs the left hemisphere appeared to be dominant. Interhemispheric asymmetry in audioparietal EPs was individual. The amplitude of the early positive component prevailed as to magnitude in the right hemisphere in males and in the left hemisphere in females. The late negative wave in animals of either sex was greater in the right hemisphere. The peculiarities of generation and interhemispheric asymmetry of different components in visual-parietal and audioparietal TCRs are discussed. A symmetricising function of the parietal associative cortex is suggested.     

The role of the posterior parietal cortex in drawing by copying

Impaired ability to draw visually presented figures by copying represents one major manifestation of constructional apraxia (CA). Previous clinical studies have indicated that CA is caused by lesions in the posterior parietal cortex (PPC), but the functional roles of the PPC remain unclear. A spared ability to trace with an impaired ability to copy indicates that deficits lie not in low-level visuomotor processing, but rather in a coordinate transformation involving production of an egocentric representation of model trajectory in the drawing space, which is spatially separated from the model space. To test the hypothesis that the PPC plays a role in coordinate transformation, we compared brain activities for drawing by copying and tracing using functional magnetic resonance imaging (fMRI). Healthy participants traced over the visually presented model or copied the model on a separate space. To avoid potential confounders of differences in behavioral performances as well as eye movements, a memory-guided condition was introduced, resulting in four drawing conditions; tracing over or copying a model at different locations (tracing and copying), with or without an on-screen model (visual and memory guidance). As hypothesized, the intraparietal sulcus (IPS) bilaterally in the PPC showed significantly greater activations in copying than in tracing, under both visual and memory guidance, with a distinct activation pattern involving the premotor and mesial motor regions. This study indicates a role of the PPC in coordinate transformation for drawing by copying, which may be important for the copying deficit observed in CA.     

Transitive inference reasoning is impaired by focal lesions in parietal cortex rather than rostrolateral prefrontal cortex

Transitive inference reasoning involves the examination and comparison of a given number of relational pairs in order to understand overall group hierarchy (e.g., A>B, B>C, C>D; therefore is A>D?). A number of imaging studies have demonstrated the role of the parietal cortex for resolving transitive inferences. Some studies also identify the rostrolateral prefrontal cortex as being critical for “relational integration” processes supporting transitive reasoning. To clarify this issue, we carried out a transitive inference study involving neurological patients with focal lesions to the rostrolateral prefrontal (n=5) or parietal cortices (n=7), as well as normal controls (n=6). The patients and controls were statistically matched on age, education, pre-injury IQ, general memory, working memory, and performance/full IQ, though the rostrolateral patients did score significantly higher than the normal controls on verbal IQ. Results indicate that patients with focal lesions to the parietal cortex were impaired in the task relative to both the patients with focal lesions to rostrolateral prefrontal cortex and the control group, and there was no difference in task performance between the rostrolateral prefrontal and the control groups. This result continued to hold after controlling for verbal IQ as a covariate. These findings point to a critical role for the parietal cortex, rather than the rostrolateral prefrontal, in transitive inference. Since the groups performed similarly on a working memory task, working memory cannot fully account for the result, suggesting a specific role of parietal cortex in transitive inference.     

Selective suppression of horizontal propagation in rat visual cortex by norepinephrine

The release of norepinephrine in the cerebral cortex from axon terminals of locus coeruleus neurons was suggested to be involved in the control of attention. Accumulating data indicate that the responses of cortical neurons are varied when norepinephrine is applied iontophoretically in the vicinity of the cells being recorded. However, it is not known how the pattern of excitatory propagation is modified when norepinephrine is applied over a wide area in the visual cortex. By applying optical imaging to rat visuocortical slices, we found a new mode of norepinephrine action; a prominent suppression of the horizontal propagation in layers II/III. This action of norepinephrine was confirmed by the simultaneous recording of field potentials from multiple sites by use of a multi-electrode dish. Furthermore, our electrophysiological recordings showed that this norepinephrine action is exerted through suppression of excitatory neural transmission and enhancement of inhibitory transmission to the pyramidal neurons in these layers. Because the release of norepinephrine in the visual cortex is regulated by the level of attention, the neural basis of visual attention may relate partially to the suppression of the integration of visual information by norepinephrine resulting in a state-dependent restructuring of the receptive field.     

Focal clonus elicited by electrical stimulation of the motor cortex in humans

Focal clonic seizures are a frequent epileptic phenomenon. However, there are little data about their pathomechanism. In four patients with focal epilepsy and subdural electrodes, focal clonus was elicited by electrical stimulation of the motor cortex. Three additional patients underwent intraoperative stimulation of the spinal cord. Rhythmic clonic muscle responses were elicited by cortical stimulation with 20-50 Hz. The clonus consisted of simultaneous trains of compound muscle action potentials (CMAP) in agonistic and antagonistic muscles alternating with periods of muscular silence despite continuous stimulation. Clonus frequency decreased from 4.0-8.0 Hz at 50 Hz stimulation to 3.0-3.5 Hz at 20 Hz paralleled by a prolongation of the trains of CMAP. The stimulation frequency correlated with the number of stimuli blocked during relaxation. During the stable stimulation periods, the clonus frequency decreased over time. The number of stimuli which formed a train of CMAP and which were blocked during relaxation increased towards the end of the stimulation periods. Increasing intensity of stimulation at the same frequency converted a clonic to a tonic response. There was always an 1:1 relationship between stimulus and CMAP during spinal cord stimulation. We hypothesize that during cortical stimulation, clonus is elicited by synchronous activation of pyramidal tract (PT) neurons which results in excitation of intracortical GABA(B)ergic interneurons by recurrent axon-collaterals. This leads to stepwise hyperpolarization of PT neurons intermittently suppressing the output of PT neurons despite continuous stimulation. This mechanism can explain our finding that temporal and spatial summation of the stimuli were needed for clonus generation.     

Visual vector inversion in the posterior parietal cortex

In the antisaccade task, a saccade must be triggered towards the mirror location of a visual target. The neural basis required for this visual vector inversion remains unclear, although neuronal activities reflecting this process have been recorded in the monkey lateral intraparietal area. We examined a patient with a small, right-sided, posterior parietal stroke who complained of difficulty in manipulating visual information. Antisaccades were markedly hypometric rightwards but normal leftwards. Largely unaffected performances in other saccade tasks revealed that visual and motor processing were not significantly affected. Antisaccade inaccuracy could therefore be ascribed to the impairment of visual vector inversion, a processing specifically required in this task. These findings provide the first evidence in humans that visual vector inversion could be an intrinsic property of the posterior parietal cortex.     

Temporal feature integration in the right parietal cortex

When searching for a target presented among distractors by means of Rapid Serial Visual Presentation (RSVP), participants often report the stimulus that is preceding or following the target as being the target. These so-called temporal binding errors are accompanied by high levels of confidence so that participants are bemused with the mismatch between their perceptual experience and the actual presented stimulus. By contrast with spatial binding the neural basis for temporal binding errors remains unexplored. Previous neuropsychology studies using non-spatial selective attention tasks have shown that right temporo-parietal cortex is involved in the temporal deployment of attention. Here we investigated the neural basis of temporal binding in five patients with visual extinction whose lesions involved different cortical areas in the right hemisphere, including the temporo-parietal cortex. Patients made significantly more binding errors for contralesional than ipsilesional stimuli and more binding errors than healthy controls. Incorrect binding from distractors near to the target was the most common for both patients and controls. Eye movements did not contribute to the pattern of results. These results show that right hemisphere cortical areas contribute to the accurate temporal coding of visual features.     

Active vision in parietal and extrastriate cortex.

Vision is an active process. We do not see the world directly; rather, we construct a representation of it from sensory inputs in combination with internal, nonvisual signals. In the case of spatial perception, our representation of the visual scene must take into account our own movements. This allows us to perceive the world as stationary despite the constant eye movements that produce new images on the retina. How is this perceptual stability achieved? Our central hypothesis is that a corollary discharge of the eye movement command updates, or remaps, an internal representation when the eyes move. In support of this hypothesis, the authors review evidence that parietal cortex and extrastriate visual areas in both monkeys and humans participate in spatial updating. These findings shed new light on the neural circuitry involved in producing a stable and coherent perception of visual space.     

Positive emotions and the right parietal cortex

The achievement of a state of solace is a developmental necessity to the unfolding of the capacity for positive emotions. In addition, solace is a significant subjective component of noninstinctual feelings such as love, joy, gratitude, and rapture. Pure solace is experienced primarily in relation to the sense of self, whereas the solace derivatives connect, in varying degrees, with objects external to the self. Psychiatrists see many patients who are unsolaceable and who, because of this, cannot experience sustained positive emotion of any kind. Those diagnosed as personality, conduct, and behaviorally disordered, as well as those with alexithymia, are particularly likely to exhibit a basic unsolaceability. The psychiatrist should also be alert to a deficiency of positive emotion in those with attention deficit disorder and the so-called learning disability syndrome. The coexistence of unsolaceability with features of right parietal cortex dysfunction suggests a directionality of positive emotional experience and parietal neocortical activity. The tertiary zones of the right parietal cortex appear to be the structural system most likely to subserve complex positive affects.     

Visuomotor functions of the posterior parietal cortex

In this special issue of Neuropsychologia leading experts in the field discuss controversies and advances in the role of the posterior parietal cortex (PPC) in visuomotor control. The papers are wide-ranging in their scope, covering monkey physiology and anatomy, functional imaging in humans and monkeys as well as transcranial magnetic stimulation and lesion studies in humans. The collection provides an important overview of the current state-of the-art in this area of research, including discussions on homologies between monkey and human parietal regions, the role of co-ordinate transformations and intermediate representations from vision to action, and reviews of controversial hot topics in this field.     

Stellate cells of the rat parietal cortex

Stellate cells have rounded or oval cell bodies which contain nuclei bounded by a ruffled, and frequently indented, nuclear envelope. Te cytoplasm of these neurons is usually darker than that of pyramidal neurons because it contains a greater concetration of ribosomes. Where the perikaryal cytoplasm is thick, the granular endoplasmic reticulum is often arranged in parallel arrays. On the surface of the perikarya are three types of synapses: (1) ones with a wide cleft and a prominent postsynaptic density, (2) ones with a wide and straight synaptic cleft that lack a prominent postsynaptic density, and (3) ones with a narrow synaptic cleft and short synaptic complexes. The dendrites of stellate cells lack spines and frequently bear many synapses. On the thinner dendritic branches the type of synapse with a side cleft and a prominent postsynaptic density is most common. The cytoplasm of the dendrites is characterized by closely arranged microtubules.     

State-dependent respiratory depression elicited by stimulation of the orbital frontal cortex

The effect of electrical stimulation of the orbital frontal cortex on respiration was studied in unanesthetized, freely moving cats across sleep-waking states. Single trains of forty 300-microA, 0.5-ms, constant-current pulses at 60 Hz were delivered to the orbital frontal cortex at four points in the respiratory cycle. Stimuli delivered during expiration produced an immediate switch to inspiration. Stimuli delivered during inspiration reduced inspiratory EMG slope and peak EMG amplitude, and prolonged inspiration. Stimuli delivered during early inspiration produced greater effects than stimuli delivered during late inspiration. Stimulation effects were elicited during quiet waking and quiet sleep but not during rapid-eye-movement sleep. These results suggest that the orbital frontal cortex may contribute to respiratory phase switching, and that its influence on brain stem structures is attenuated during rapid-eye-movement sleep.     

Dorsal visual cortex activity elicited by posture change in a visuo-tactile matching task

To investigate the process of crossmodal spatial recognition, we examined the effect of posture change on the recognition of a tactile stimulus position. The task was to judge whether a visual and a tactile stimulus, presented to the left or right, were on the same or different sides while subjects crossed or uncrossed their hands. Under a condition which removed the effect of response bias to the left and right, the dorsal visual cortex (area 18/19) and the precuneus were more activated in the crossed hands condition. The dorsal visual cortex activation suggests that the activity of brain areas classically considered to be visual cortex is affected by posture change, and reflects the reciprocal process across different modalities in spatial recognition.     

Eye position encoding in the macaque posterior parietal cortex

In two previous studies, we had demonstrated the influence of eye position on neuronal discharges in the middle temporal area, medial superior temporal area, lateral intraparietal area and area 7A of the awake monkey ( Bremmer et al. 1997a , b). Eye position effects also have been found in visual cortical areas V3A and V6 and even in the premotor cortex and the supplementary eye field. These effects are generally discussed in light of a coordinate transformation of visual signals into a non-retinocentric frame of reference. Neural network studies dealing with the eye position effect succeeded in constructing such non-retinocentric representations by using model neurones whose response characteristics resembled those of ‘real’ neurones. However, to our knowledge, response properties of real neurones never acted as input into these neural networks. In the present study, we thus investigated whether, theoretically, eye position could be estimated from the population discharge of the (previously) recorded neurones and, if so, we intended to develop an encoding algorithm for the position of the eyes in the orbit. The optimal linear estimator proved the capability of the ensemble activity for determining correctly eye position. We then developed the so-called subpopulation encoding of eye position. This algorithm is based on the partition of the ensemble of neurones into two pairs of subpopulations. Eye position is represented by the differences of activity levels within each pair of subpopulations. Considering this result, encoding of the location of an object relative to the head could easily be accomplished by combining eye position information with the intrinsic knowledge about the retinal location of a visual stimulus. Taken together, these results show that throughout the monkey’s visual cortical system information is available which can be used in a fairly simple manner in order to generate a non-retinocentric representation of visual information.     

Operant conditioning of single unit activity in parietal cortex

Two rhesus monkeys were trained to control firing patterns of single neurons in parietal cortex (areas 1, 2, 3, 5, 7) using an operant task previously applied to the study of precental units. Twenty-four of 56 (43%) postcentral cells were controlled in contrast to 71 of 136 (52%) precentral units from these and 4 other rhesus monkeys. In addition, monkeys were able to drive precentral units to more sustained tonic firing rates than they could parietal units.An analysis of interspike interval (ISI) distributions showed that, in contrast to precentral units with modal ISIs of 25–50 ms, 50% of parietal units have modal ISIs of 2 ms. Such short ISIs may account for fewer postcentral units reaching control criteria for this particular operant task. Other factors that may contribute to the reduced control of postcentral cells are discussed, particularly the more complex afferent connections to parietal units when compared to precentral pyramidal tract neurons.The data indirectly support conclusions from previous studies that imply that operant control of cortical units is peripherally mediated and does not primarily involve a ‘central’ or ‘open loop’ system.