Characterization of Ultrasonic Vocalization-Modulated Neurons in Rat Motor Cortex Based on Their Activity Modulation and Axonal Projection to the Periaqueductal Gray.

Vocalization, a means of social communication, is prevalent among many species, including humans. Both rats and mice use ultrasonic vocalizations (USVs) in various social contexts and affective states. The motor cortex is hypothesized to be involved in precisely controlling USVs through connections with critical regions of the brain for vocalization, such as the periaqueductal gray matter (PAG). However, it is unclear how neurons in the motor cortex are modulated during USVs. Moreover, the relationship between USV modulation of neurons and anatomical connections from the motor cortex to PAG is also not clearly understood. In this study, we first characterized the activity patterns of neurons in the primary and secondary motor cortices during emission of USVs in rats using large-scale electrophysiological recordings. We also examined the axonal projection of the motor cortex to PAG using retrograde labeling and identified two clusters of PAG-projecting neurons in the anterior and posterior parts of the motor cortex. The neural activity patterns around the emission of USVs differed between the anterior and posterior regions, which were divided based on the distribution of PAG-projecting neurons in the motor cortex. Furthermore, using optogenetic tagging, we recorded the USV modulation of PAG-projecting neurons in the posterior part of the motor cortex and found that they showed predominantly sustained excitatory responses during USVs. These results contribute to our understanding of the involvement of the motor cortex in the generation of USV at the neuronal and circuit levels.

Electroencephalographic Effective Connectivity Analysis of the Neural Networks during Gesture and Speech Production Planning in Young Adults.

Gestures and speech, as linked communicative expressions, form an integrated system. Previous functional magnetic resonance imaging studies have suggested that neural networks for gesture and spoken word production share similar brain regions consisting of fronto-temporo-parietal brain regions. However, information flow within the neural network may dynamically change during the planning of two communicative expressions and also differ between them. To investigate dynamic information flow in the neural network during the planning of gesture and spoken word generation in this study, participants were presented with spatial images and were required to plan the generation of gestures or spoken words to represent the same spatial situations. The evoked potentials in response to spatial images were recorded to analyze the effective connectivity within the neural network. An independent component analysis of the evoked potentials indicated 12 clusters of independent components, the dipoles of which were located in the bilateral fronto-temporo-parietal brain regions and on the medial wall of the frontal and parietal lobes. Comparison of effective connectivity indicated that information flow from the right middle cingulate gyrus (MCG) to the left supplementary motor area (SMA) and from the left SMA to the left precentral area increased during gesture planning compared with that of word planning. Furthermore, information flow from the right MCG to the left superior frontal gyrus also increased during gesture planning compared with that of word planning. These results suggest that information flow to the brain regions for hand praxis is more strongly activated during gesture planning than during word planning.

Suppressive effects of ketamine on auditory steady-state responses in intact, awake macaques: A non-human primate model of schizophrenia.

Auditory steady-state responses (ASSRs) are recurrent neural activities entrained to regular cyclic auditory stimulation. ASSRs are altered in individuals with schizophrenia, and may be related to hypofunction of the N-methyl-D-aspartate (NMDA) glutamate receptor. Noncompetitive NMDA receptor antagonists, including ketamine, have been used in ASSR studies of rodent models of schizophrenia. Although animal studies using non-human primates are required to complement rodent studies, the effects of ketamine on ASSRs are unknown in intact awake non-human primates. In this study, after administration of vehicle or ketamine, click trains at 20-83.3 Hz were presented to elicit ASSRs during recording of electroencephalograms in intact, awake macaque monkeys. The results indicated that ASSRs quantified by event-related spectral perturbation and inter-trial coherence were maximal at 83.3 Hz after vehicle administration, and that ketamine reduced ASSRs at 58.8 and 83.3 Hz, but not at 20 and 40 Hz. The present results demonstrated a reduction of ASSRs by the NMDA receptor antagonist at optimal frequencies with maximal responses in intact, awake macaques, comparable to ASSR reduction in patients with schizophrenia. These findings suggest that ASSR can be used as a neurophysiological biomarker of the disturbance of gamma-oscillatory neural circuits in this ketamine model of schizophrenia using intact, awake macaques. Thus, this model with ASSRs would be useful in the investigation of human brain pathophysiology as well as in preclinical translational research.

Neuronal structures controlling locomotor behavior during active and inactive motor states.

Animal behaviors can be divided into two states according to their motor activity: the active motor state, which involves significant body movements, and the inactive motor state, which refers to when the animal is stationary. The timing and duration of these states are determined by the activity of the neuronal circuits involved in motor control. Among these motor circuits, those that generate locomotion are some of the most studied neuronal networks and are widely distributed from the spinal cord to the cerebral cortex. In this review, we discuss recent discoveries, mainly in rodents using state-of-the-art experimental approaches, of the neuronal mechanisms underlying the initiation and termination of locomotion in the brainstem, basal ganglia, and prefrontal cortex. These findings is discussed with reference to studies on the neuronal mechanism of motor control during sleep and the modulation of cortical states in these structures. Accumulating evidence has unraveled the complex yet highly structured network that controls the transition between motor states.

Neural basis of topographical disorientation in the primate posterior cingulate gyrus based on a labeled graph.

Patients with lesions in the posterior cingulate gyrus (PCG), including the retrosplenial cortex (RSC) and posterior cingulate cortex (PCC), cannot navigate in familiar environments, nor draw routes on a 2D map of the familiar environments. This suggests that the topographical knowledge of the environments (i.e., cognitive map) to find the right route to a goal is represented in the PCG, and the patients lack such knowledge. However, theoretical backgrounds in neuronal levels for these symptoms in primates are unclear. Recent behavioral studies suggest that human spatial knowledge is constructed based on a labeled graph that consists of topological connections (edges) between places (nodes), where local metric information, such as distances between nodes (edge weights) and angles between edges (node labels), are incorporated. We hypothesize that the population neural activity in the PCG may represent such knowledge based on a labeled graph to encode routes in both 3D environments and 2D maps. Since no previous data are available to test the hypothesis, we recorded PCG neuronal activity from a monkey during performance of virtual navigation and map drawing-like tasks. The results indicated that most PCG neurons responded differentially to spatial parameters of the environments, including the place, head direction, and reward delivery at specific reward areas. The labeled graph-based analyses of the data suggest that the population activity of the PCG neurons represents the distance traveled, locations, movement direction, and navigation routes in the 3D and 2D virtual environments. These results support the hypothesis and provide a neuronal basis for the labeled graph-based representation of a familiar environment, consistent with PCG functions inferred from the human clinicopathological studies.

Young female participants show blunted placebo effects associated with blunted responses to a cue predicting a safe stimulus in the right dorsolateral prefrontal cortex.

Discrimination of cues predicting non-nociceptive/nociceptive stimuli is essential for predicting whether a non-painful or painful stimulus will be administered and for eliciting placebo/nocebo (pain reduction/pain enhancement) effects. Dysfunction of the neural system involved in placebo effects has been implicated in the pathology of chronic pain, while female sex is one of the important risk factors for development of chronic pain in young adults. The dorsolateral prefrontal cortex (dl-PFC) is suggested to be involved in placebo effects and is sensitive to sex and age. In this study, to examine the neural mechanisms by which sex and age alter placebo and nocebo effects, we analyzed cerebral hemodynamic activities in the dl-PFC in different sex and age groups during a differential conditioning task. During the training session, two different sounds were followed by low- and high-intensity electrical shocks. In the following recording session, electrical shocks, the intensity of which was mismatched to the sounds, were occasionally administered to elicit placebo and nocebo effects. In young female participants, both placebo effects and hemodynamic responses to the conditioned sounds in the right dl-PFC were significantly lower than those in elderly female participants, while there were no age differences in male participants. The hemodynamic responses to the sound paired with the safe stimulus in the right dl-PFC were significantly correlated with placebo effects, except in the young female group. These results suggest that blunted placebo effects in the young female participants are ascribed to blunted responses to the sound associated with the safe stimulus in the right dl-PFC, and that sex- and age-related factors may alter the responsiveness of the right dl-PFC to associative cues predicting a safe stimulus.

Characteristics of auditory steady-state responses to different click frequencies in awake intact macaques.

BACKGROUND: Auditory steady-state responses (ASSRs) are periodic evoked responses to constant periodic auditory stimuli, such as click trains, and are suggested to be associated with higher cognitive functions in humans. Since ASSRs are disturbed in human psychiatric disorders, recording ASSRs from awake intact macaques would be beneficial to translational research as well as an understanding of human brain function and its pathology. However, ASSR has not been reported in awake macaques. RESULTS: Electroencephalograms (EEGs) were recorded from awake intact macaques, while click trains at 20-83.3 Hz were binaurally presented. EEGs were quantified based on event-related spectral perturbation (ERSP) and inter-trial coherence (ITC), and ASSRs were significantly demonstrated in terms of ERSP and ITC in awake intact macaques. A comparison of ASSRs among different click train frequencies indicated that ASSRs were maximal at 83.3 Hz. Furthermore, analyses of laterality indices of ASSRs showed that no laterality dominance of ASSRs was observed. CONCLUSIONS: The present results demonstrated ASSRs, comparable to those in humans, in awake intact macaques. However, there were some differences in ASSRs between macaques and humans: macaques showed maximal ASSR responses to click frequencies higher than 40 Hz that has been reported to elicit maximal responses in humans, and showed no dominant laterality of ASSRs under the electrode montage in this study compared with humans with right hemisphere dominance. The future ASSR studies using awake intact macaques should be aware of these differences, and possible factors, to which these differences were ascribed, are discussed.

Acoustic camera system for measuring ultrasound communication in mice.

To investigate biological mechanisms underlying social behaviors and their deficits, social communication via ultrasonic vocalizations (USVs) in mice has received considerable attention as a powerful experimental model. The advances in sound localization technology have facilitated the analysis of vocal interactions between multiple mice. However, existing sound localization systems are built around distributed-microphone arrays, which require a special recording arena and long processing time. Here, we report a novel acoustic camera system, USVCAM, which enables simpler and faster USV localization and assignment. The system comprises recently developed USV segmentation algorithms with a modification for overlapping vocalizations that results in high accuracy. Using USVCAM, we analyzed USV communications in a conventional home cage, and demonstrated novel vocal interactions in female ICR mice under a resident-intruder paradigm. The extended applicability and usability of USVCAM may facilitate future studies investigating typical and atypical vocal communication and social behaviors, as well as the underlying mechanisms.

Fast Detection of Snakes and Emotional Faces in the Macaque Amygdala.

Primate vision is reported to detect snakes and emotional faces faster than many other tested stimuli. Because the amygdala has been implicated in avoidance and emotional behaviors to biologically relevant stimuli and has neural connections with subcortical nuclei involved with vision, amygdalar neurons would be sensitive to snakes and emotional faces. In this study, neuronal activity in the amygdala was recorded from Japanese macaques (Macaca fuscata) during discrimination of eight categories of visual stimuli including snakes, monkey faces, human faces, carnivores, raptors, non-predators, monkey hands, and simple figures. Of 527 amygdalar neurons, 95 responded to one or more stimuli. Response characteristics of the amygdalar neurons indicated that they were more sensitive to the snakes and emotional faces than other stimuli. Response magnitudes and latencies of amygdalar neurons to snakes and monkey faces were stronger and faster than those to the other categories of stimuli, respectively. Furthermore, response magnitudes to the low pass-filtered snake images were larger than those to scrambled snake images. Finally, analyses of population activity of amygdalar neurons suggest that snakes and emotional faces were represented separately from the other stimuli during the 50-100 ms period from stimulus onset, and neutral faces during the 100-150 ms period. These response characteristics indicate that the amygdala processes fast and coarse visual information from emotional faces and snakes (but not other predators of primates) among the eight categories of the visual stimuli, and suggest that, like anthropoid primate visual systems, the amygdala has been shaped over evolutionary time to detect appearance of potentially threatening stimuli including both emotional faces and snakes, the first of the modern predators of primates.

Contributions of the Monkey Inferior Temporal Areas TE and TEO to Visual Categorization.

The ability to categorize images is thought to depend on neural processing within the ventral visual stream. Recently, we reported that after removal of architectonic area TE, the terminal region of the ventral stream, monkeys were still able to categorize images as cats or dogs moderately well. Here, we investigate the contribution of TEO, the architectonically defined region located one step earlier than area TE in the ventral stream. Bilateral removal of TEO caused only a mild impairment in categorization. However, combined TE + TEO removal was followed by a severe, long-lasting impairment in categorization. All of the monkeys tested, including those with combined TE + TEO removals, had normal low-level visual functions, such as visual acuity. These results support the conclusion that categorization based on visual similarity is processed in parallel in TE and TEO.

Preferential Neuronal Responses to Snakes in the Monkey Medial Prefrontal Cortex Support an Evolutionary Origin for Ophidiophobia.

Ophidiophobia (snake phobia) is one of the most common specific phobias. It has been proposed that specific phobia may have an evolutionary origin, and that attentional bias to specific items may promote the onset of phobia. Noninvasive imaging studies of patients with specific phobia reported that the medial prefrontal cortex (mPFC), especially the rostral part of the anterior cingulate cortex (rACC), and amygdala are activated during the presentation of phobogenic stimuli. We propose that the mPFC-amygdala circuit may be involved in the pathogenesis of phobia. The mPFC receives inputs from the phylogenically old subcortical visual pathway including the superior colliculus, pulvinar, and amygdala, while mPFC neurons are highly sensitive to snakes that are the first modern predator of primates, and discriminate snakes with striking postures from those with non-striking postures. Furthermore, the mPFC has been implicated in the attentional allocation and promotes amygdala-dependent aversive conditioning. These findings suggest that the rACC focuses attention on snakes, and promotes aversive conditioning to snakes, which may lead to anxiety and ophidiophobia.

Examination of the Prefrontal Cortex Hemodynamic Responses to the Fist-Edge-Palm Task in Naïve Subjects Using Functional Near-Infrared Spectroscopy.

The Fist-Edge-Palm (FEP) task, a manual hand task, has been used to detect frontal dysfunctions in clinical situations: its performance failures are observed in various prefrontal cortex (PFC)-related disorders, including schizophrenia. However, previous imaging studies reported that the performance of the FEP task activated motor-related areas, but not the PFC. Here, we aimed to investigate the relationships between the performance of the FEP task and PFC functions. Hemodynamic activity in the PFC, including the dorsolateral PFC (area 46) and frontal pole (area 10), was recorded. Healthy young subjects performed the FEP task as well as a palm tapping (PT) task (control task) three times. The subjects also completed a Wisconsin Card Sorting Test (WCST) and Schizotypal Personality Scale (STA) questionnaire. We found that hemodynamic activity (Oxy-Hb) in the PFC increased in the first trial of the FEP task but decreased considerably in the second and third trials compared to the PT task. The number of performance errors in the FEP task also decreased in the second and third trials. Error reduction (i.e., learning) in the FEP task between the first and second trials was negatively correlated with schizotypal trait and the number of perseveration errors in the WCST. Furthermore, changes in the PFC hemodynamic activity between the first and second trials were positively correlated with error reduction in the FEP task between the first and second trials, and negatively correlated with the number of perseveration errors in the WCST. These results suggest that learning in the FEP task requires PFC activation, which is negatively associated with perseveration errors in the WCST. The results further suggest that the FEP task, in conjunction with near-infrared spectroscopy, may be useful as a diagnostic method for various disorders with PFC dysfunction.

Involvement of Parvalbumin-Positive Neurons in the Development of Hyperalgesia in a Mouse Model of Fibromyalgia.

Fibromyalgia (FM) presents as chronic systemic pain, which might be ascribed to central sensitization, in which pain information processing is amplified in the central nervous system. Since patients with FM display elevated gamma oscillations in the pain matrix and parvalbumin (PV)-positive neurons play a critical role in induction of gamma oscillations, we hypothesized that changes in PV-positive neurons are involved in hyperalgesia in fibromyalgia. In the present study, to investigate a role of PV-positive neurons in neuropathic pain, mice received reserpine administration for 3 consecutive days as an animal model of FM (RES group), while control mice received vehicle injections in the same way (VEH group). The mice were subjected to hot-plate and forced swim tests, and immuno-stained PV-positive neurons were counted in the pain matrix. We investigated relationships between PV-positive neuron density in the pain matrix and pain avoidance behaviors. The results indicated that the mice in the RES group showed transient bodyweight loss and longer immobility time in the forced swim test than the mice in the VEH group. In the hot-plate test, the RES group showed shorter response latencies and a larger number of jumps in response to nociceptive thermal stimulus than the VEH group. Histological examination indicated an increase in the density of PV-positive neurons in the primary somatosensory cortex (S1) in the RES group. Furthermore, response latencies to the hot-plate were significantly and negatively correlated with the density of PV-positive neurons in the S1. These results suggest a critical role for PV-positive neurons in the S1 to develop hyperalgesia in FM.

Recency memory effects in Macaques during sequential delayed match-to-sample task with visual noise.

Visual object recognition requires both visual sensory information and memory, and its mechanisms are often studied using old-world monkeys. Wittig et al. (2014, 2016) reported that Rhesus monkeys and humans seem to adopt different strategies in a short-term visual memory task. The Rhesus monkeys seemed to rely on recency of stimulus repetition, whereas humans relied on specific memorization. We conducted experiments using a sequential delayed match-to-sample task with random dot visual noise using Rhesus and Japanese monkeys and found that recency effect was observed in both species. There were differences in the noise effect on behavioral performances across species.

Reverse-filtering on extracellular action potential for waveform analysis.

For further understanding the role of serotonergic neurons, unit recordings using behaving primates are increasingly needed. A widely used criterion to identify serotonergic neuron relies on the duration of extracellular action potential (EAP). However, the duration is inaccurate due to the passband limitation needed to carry out the spike sorting. To restore an original waveform, we conducted 1) averaging the EAPs collected from the unfiltered raw signal and 2) reverse-filtering the EAPs collected from the filtered raw signal. The reconstructed waveforms by these analyses well agreed with each other, suggesting that either analysis is applicable to restore the EAPs. Even using multivariate analyses, the reconstructed EAPs in dorsal raphe (DR) could not be divided into different clusters possibly related to neurochemicals, suggesting that the DR neurons in the previous studies that relied on waveform criterion might contain both serotonergic and non-serotonergic neurons. Between DR and orbitofrontal cortex (OFC), there were no differences in the duration of filtered EAPs. However, against the conventional criterion, the duration of the first crest in the unfiltered / restored EAPs in DR that might contain serotonergic neurons was shorter than that in OFC. This raises a possibility that the conventional waveform criterion needs further consideration.

The effect of 5-HT1A receptor antagonist on reward-based decision-making.

When choosing the best action from several alternatives, we compare each value that depends on the balance between benefit and cost. Previous studies have shown that animals and humans with low brain serotonin (5-HT) level tend to choose smaller immediate reward. We used a decision-making schedule task to investigate whether 5-HT1A receptor is responsible for the decisions related to reward. In this task, the monkeys chose either of two different alternatives that were comprised of 1-4 drops of liquid reward (benefit) and 1-4 repeats of a color discrimination trial (workload cost), then executed the chosen schedule. By the administration of 5-HT1A antagonist, WAY100635, the choice tendency did not change, however, the sensitivity to the amount of reward in the schedule part was diminished. The 5-HT1A could have a role in maintaining reward value to keep track with the promised reward rather than modulating workload discounting of reward value.

Temporal Coding of Reward Value in Monkey Ventral Striatal Tonically Active Neurons.

The rostromedioventral striatum is critical for behavior dependent on evaluating rewards. We asked what contribution tonically active neurons (TANs), the putative striatal cholinergic interneurons, make in coding reward value in this part of the striatum. Two female monkeys were given the option to accept or reject an offered reward in each trial, the value of which was signaled by a visual cue. Forty-five percent of the TANs use temporally modulated activity to encode information about discounted value. These responses were significantly better represented using principal component analysis than by just counting spikes. The temporal coding is straightforward: the spikes are distributed according to a sinusoidal envelope of activity that changes gain, ranging from positive to negative according to discounted value. Our results show that the information about the relative value of an offered reward is temporally encoded in neural spike trains of TANs. This temporal coding may allow well tuned, coordinated behavior to emerge.SIGNIFICANCE STATEMENT Ever since the discovery that neurons use trains of pulses to transmit information, it seemed self-evident that information would be encoded into the pattern of the spikes. However, there is not much evidence that spike patterns encode cognitive information. We find that a set of interneurons, the tonically active neurons (TANs) in monkeys' striatum, use temporal patterns of response to encode information about the discounted value of offered rewards. The code seems straightforward: a sinusoidal envelope that changes gain according to the discounted value of the offer, describes the rate of spiking across time. This temporal modulation may provide a means to synchronize these interneurons and the activity of other neural elements including principal output neurons.

Neurons in the monkey orbitofrontal cortex mediate reward value computation and decision-making.

Choice reflects the values of available alternatives; more valuable options are chosen more often than less valuable ones. Here we studied whether neuronal responses in orbitofrontal cortex (OFC) reflect the value difference between options, and whether there is a causal link between OFC neuronal activity and choice. Using a decision-making task where two visual stimuli were presented sequentially, each signifying a value, we showed that when the second stimulus appears many neurons encode the value difference between alternatives. Later when the choice occurs, that difference signal disappears and a signal indicating the chosen value emerges. Pharmacological inactivation of OFC neurons coding for choice-related values increases the monkey's latency to make a choice and the likelihood that it will choose the less valuable alternative, when the value difference is small. Thus, OFC neurons code for value information that could be used to directly influence choice.

Self-choice enhances value in reward-seeking in primates.

When an individual chooses one item from two or more alternatives, they compare the values of the expected outcomes. The outcome value can be determined by the associated reward amount, the probability of reward, and the workload required to earn the reward. Rational choice theory states that choices are made to maximize rewards over time, and that the same outcome values lead to an equal likelihood of choices. However, the theory does not distinguish between conditions with the same reward value, even when acquired under different circumstances, and does not always accurately describe real behavior. We have found that allowing a monkey to choose a reward schedule endows the schedule with extra value when compared to performance in an identical schedule that is chosen by another agent (a computer here). This behavior is not consistent with pure rational choice theory. Theoretical analysis using a modified temporal-difference learning model showed an enhanced schedule state value by self-choice. These results suggest that an increased reward value underlies the improved performances by self-choice during reward-seeking behavior.

Neurons in monkey dorsal raphe nucleus code beginning and progress of step-by-step schedule, reward expectation, and amount of reward outcome in the reward schedule task.

The dorsal raphe nucleus is the major source of serotonin in the brain. It is connected to brain regions related to reward processing, and the neurons show activity related to predicted reward outcome. Clinical observations also suggest that it is important in maintaining alertness and its apparent role in addiction seems to be related to reward processing. Here, we examined whether the neurons in dorsal raphe carry signals about reward outcome and task progress during multitrial schedules. We recorded from 98 single neurons in dorsal raphe of two monkeys. The monkeys perform one, two, or three visual discrimination trials (schedule), obtaining one, two, or three drops of liquid. In the valid cue condition, the length and brightness of a visual cue indicated schedule progress and reward amount, respectively. In the random cue condition, the visual cue was randomly presented with respect to schedule length and reward amount. We found information encoded about (1) schedule onset, (2) reward expectation, (3) reward outcome, and (4) reward amount in the mean firing rates. Information theoretic analysis showed that the temporal variation of the neuronal responses contained additional information related to the progress of the schedule toward the reward rather than only discriminating schedule onset or reward/no reward. When considered in light of all that is known about the raphe in anatomy, physiology, and behavior, the rich encoding about both task progress and predicted reward outcome makes the raphe a strong candidate for providing signals throughout the brain to coordinate persistent goal-seeking behavior.