Single neurons in posterior parietal cortex of monkeys encode cognitive set

The primate posterior parietal cortex (PPC), part of the dorsal visual pathway, is best known for its role in encoding salient spatial information. Yet there are indications that neural activity in the PPC can also be modulated by nonspatial task-related information. In this study, we tested whether neurons in the PPC encode signals related to cognitive set, that is, the preparation to perform a particular task. Cognitive set has previously been associated with the frontal cortex but not the PPC. In this study, monkeys performed a cognitive set shifting paradigm in which they were cued in advance to apply one of two different task rules to the subsequent stimulus on every trial. Here we show that a subset of neurons in the PPC, concentrated in the lateral bank of the intraparietal sulcus and on the angular gyrus, responds selectively to cues for different task rules.     

Posterior parietal cortex: Space--and beyond

How do we decide how to react to a stimulus or event? To do so requires recognition of the stimulus itself as well as an appreciation of the context within which that stimulus is encountered. In this issue of Neuron, Stoet and Snyder report that neurons in the parietal cortex of monkeys can carry contextual information related to the rules that are relevant for solving a visual discrimination task.     

Posterior parietal cortex encodes autonomously selected motor plans

The posterior parietal cortex (PPC) of rhesus monkeys has been found to encode the behavioral meaning of categories of sensory stimuli. When animals are instructed with sensory cues to make either eye or hand movements to a target, PPC cells also show specificity depending on which effector (eye or hand) is instructed for the movement. To determine whether this selectivity retrospectively reflects the behavioral meaning of the cue or prospectively encodes the movement plan, we trained monkeys to autonomously choose to acquire a target in the absence of direct instructions specifying which effector to use. Activity in PPC showed strong specificity for effector choice, with cells in the lateral intraparietal area selective for saccades and cells in the parietal reach region selective for reaches. Such differential activity associated with effector choice under identical stimulus conditions provides definitive evidence that the PPC is prospectively involved in action selection and movement preparation.     

Only coherent spiking in posterior parietal cortex coordinates looking and reaching

Here, we report that temporally patterned, coherent spiking activity in the posterior parietal cortex (PPC) coordinates the timing of looking and reaching. Using a spike-field approach, we identify a population of parietal area LIP neurons that fire spikes coherently with 15 Hz beta-frequency LFP activity. The firing rate of coherently active neurons predicts the reaction times (RTs) of coordinated reach-saccade movements but not of saccades when made alone. Area LIP neurons that do not fire coherently do not predict RT of either movement type. Similar beta-band LFP activity is present in the parietal reach region but not nearby visual area V3d. This suggests that coherent spiking activity in PPC can control reaches and saccades together. We propose that the neural mechanism of coordination involves a shared representation that acts to slow or speed movements together.     

Insular cortex neurons encode and retrieve specific immune responses

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Neural correlates of social target value in macaque parietal cortex

Animals as diverse as arthropods [1], fish [2], reptiles [3], birds [4], and mammals, including primates [5], depend on visually acquired information about conspecifics for survival and reproduction. For example, mate localization often relies on vision [6], and visual cues frequently advertise sexual receptivity or phenotypic quality [5]. Moreover, recognizing previously encountered competitors or individuals with preestablished territories [7] or dominance status [1, 5] can eliminate the need for confrontation and the associated energetic expense and risk for injury. Furthermore, primates, including humans, tend to look toward conspecifics and objects of their attention [8, 9], and male monkeys will forego juice rewards to view images of high-ranking males and female genitalia [10]. Despite these observations, we know little about how the brain evaluates social information or uses this appraisal to guide behavior. Here, we show that neurons in the primate lateral intraparietal area (LIP), a cortical area previously linked to attention and saccade planning [11, 12], signal the value of social information when this assessment influences orienting decisions. In contrast, social expectations had no impact on LIP neuron activity when monkeys were not required to make a choice. These results demonstrate for the first time that parietal cortex carries abstract, modality-independent target value signals that inform the choice of where to look.     

fMRI adaptation reveals mirror neurons in human inferior parietal cortex

Mirror neurons, as originally described in the macaque, have two defining properties [1, 2]: They respond specifically to a particular action (e.g., bringing an object to the mouth), and they produce their action-specific responses independent of whether the monkey executes the action or passively observes a conspecific performing the same action. In humans, action observation and action execution engage a network of frontal, parietal, and temporal areas. However, it is unclear whether these responses reflect the activity of a single population that represents both observed and executed actions in a common neural code or the activity of distinct but overlapping populations of exclusively perceptual and motor neurons [3]. Here, we used fMRI adaptation to show that the right inferior parietal lobe (IPL) responds independently to specific actions regardless of whether they are observed or executed. Specifically, responses in the right IPL were attenuated when participants observed a recently executed action relative to one that had not previously been performed. This adaptation across action and perception demonstrates that the right IPL responds selectively to the motoric and perceptual representations of actions and is the first evidence for a neural response in humans that shows both defining properties of mirror neurons.     

Dynamic social adaptation of motion-related neurons in primate parietal cortex

Social brain function, which allows us to adapt our behavior to social context, is poorly understood at the single-cell level due largely to technical limitations. But the questions involved are vital: How do neurons recognize and modulate their activity in response to social context? To probe the mechanisms involved, we developed a novel recording technique, called multi-dimensional recording, and applied it simultaneously in the left parietal cortices of two monkeys while they shared a common social space. When the monkeys sat near each other but did not interact, each monkey's parietal activity showed robust response preference to action by his own right arm and almost no response to action by the other's arm. But the preference was broken if social conflict emerged between the monkeys-specifically, if both were able to reach for the same food item placed on the table between them. Under these circumstances, parietal neurons started to show complex combinatorial responses to motion of self and other. Parietal cortex adapted its response properties in the social context by discarding and recruiting different neural populations. Our results suggest that parietal neurons can recognize social events in the environment linked with current social context and form part of a larger social brain network.     

Effects of enkephalins on associative processes of parietal cortex neurons

Experiments on cats examined the effect of met- and leu-enkephalins on the process of learning of the parietal associative cortex neurons (field 5). It has been shown that conditioned electrical stimulation of the pyramidal tract axons with nociceptive reinforcement evoked plastic changes of responses in 35 neurons. It was found that the effect of microiontophoretically applied enkephalins on these neurons depend on the time of iontophoretic application. When endogenous opioid peptides were applied up to 30-40 min they inhibited the process of elaboration of temporary connection.     

Representation of time by neurons in the posterior parietal cortex of the macaque

The neural basis of time perception is unknown. Here we show that neurons in the posterior parietal cortex (area LIP) represent elapsed time relative to a remembered duration. We trained rhesus monkeys to report whether the duration of a test light was longer or shorter than a remembered "standard" (316 or 800 ms) by making an eye movement to one of two choice targets. While timing the test light, the responses of LIP neurons signaled changes in the monkey's perception of elapsed time. The variability of the neural responses explained the monkey's uncertainty about its temporal judgments. Thus, in addition to their role in spatial processing and sensorimotor integration, posterior parietal neurons encode signals related to the perception of time.     

Human parietal cortex in action

Experiments using functional neuroimaging and transcranial magnetic stimulation in humans have revealed regions of the parietal lobes that are specialized for particular visuomotor actions, such as reaching, grasping and eye movements. In addition, the human parietal cortex is recruited by processing and perception of action-related information, even when no overt action occurs. Such information can include object shape and orientation, knowledge about how tools are employed and the understanding of actions made by other individuals. We review the known subregions of the human posterior parietal cortex and the principles behind their organization.     

Neurophysiological analysis of efferent-afferent interaction of neurons of the parietal associate cortex in cats

Neuronal responses of the parietal associate cortex (field 5) was recorded in waking cat during electrical stimulation of the pyramidal tract axons and afferent stimulation. The electrical stimulation of the pyramid evoked marked responses in 39% of neurons. 87% of these neurons increased spike activity during sematic nociceptive stimulation, 61% of test neurons were activated by light or tonal stimulation. Neuronal activity was recorded during defensive conditioning to the pyramidal tract axons stimulation. It has been shown that conditioned stimulation of the pyramidal tract evoked plastic changes of responses in 66% of neurons of the parietal cortex. These data are discussed relative to the possible functional role of the efferent-afferent interaction to field 5.     

Response of parietal association cortex neurons to acoustic stimulation before and after auditory cortex blockage in the cat

The effect of auditory cortex blockade on response patterns of parietal association cortex neurons responding to different frequency tones was investigated in the cat. Blockade was produced by two methods: bilateral isolation and application of a 6% Nembutal solution to the auditory cortex surface. Frequency threshold curves were plotted for all test neurons. The majority of test neurons (84%) displayed one or two characteristic frequencies before blockade, as against only 63% of all neurons responding following blockade. Changes also affect the range of frequencies at which the cells could respond. Virtually all test neurons responded to application of a broad spectrum of frequencies under normal conditions. After blockade of the auditory cortex 69% of neurons no longer responded to tones above 8–10 kHz. This would suggest that mainly information on high frequency tones is transmitted via the auditory cortex. The question of where acoustic information for parietal association cortex neurons mostly originates is also discussed; association thalamic nuclei are thought to be the main source.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 18, No. 3, pp. 354–360, May–June, 1986.     

Atomic motion in enzymatic reaction coordinates

Atomic excursions of reactants in enzymatic catalytic sites can be estimated from high-resolution crystal structures of enzyme complexes with substrates, transition state analog inhibitors and products. Transition state structures, defined from kinetic isotope effect studies, are compared to crystallographic structures to validate the properties of the transition state analog. Atomic excursions in enzymatic catalytic sites can differ from those in solution and define the role of the enzymatic catalyst in directing atomic motion.     

Spatial updating in human parietal cortex

Single neurons in monkey parietal cortex update visual information in conjunction with eye movements. This remapping of stimulus representations is thought to contribute to spatial constancy. We hypothesized that a similar process occurs in human parietal cortex and that we could visualize it with functional MRI. We scanned subjects during a task that involved remapping of visual signals across hemifields. We observed an initial response in the hemisphere contralateral to the visual stimulus, followed by a remapped response in the hemisphere ipsilateral to the stimulus. We ruled out the possibility that this remapped response resulted from either eye movements or visual stimuli alone. Our results demonstrate that updating of visual information occurs in human parietal cortex.     

Activity of the parietal associative cortex neurons and aminergic brainstem neurons at the performance of a voluntary movement in cats

Activity of 98 neurons of the parietal associative cortex (PAC) and 189 supposedly aminergic brainstem neurons (dopaminergic in thesubstantia nigra pans compacta, noradrenergic in thelocus coeruleus region, and serotonergic in theraphe nuclei) was recorded in awake cats. The animals were trained to perform a voluntary movement (pressing a pedal) not earlier than at a certain prefixed time moment. More than half of the recorded units modified their activity before the movement initiation. The PAC neurons responded mostly within the interval of planning of the movement, while reactions of aminergic neurons were observed in the course of its initiation, which probably provides facilitation of the responses of cortical neurons. The pattern of responses was rather specific for each of the studied neuronal populations.