Electroencephalography Measurements in Awake Marmosets Listening to Conspecific Vocalizations.

Vocal communication plays a crucial role in the social interactions of primates, particularly in survival and social organization. Humans have developed a unique and advanced vocal communication strategy in the form of language. To study the evolution of human language, it is necessary to investigate the neural mechanisms underlying vocal processing in humans, as well as to understand how brain mechanisms have evolved by comparing them with those in nonhuman primates. Herein, we developed a method to noninvasively measure the electroencephalography (EEG) of awake nonhuman primates. This recording method allows for long-term studies without harming the animals, and, importantly, allows us to directly compare nonhuman primate EEG data with human data, providing insights into the evolution of human language. In the current study, we used the scalp EEG recording method to investigate brain activity in response to species-specific vocalizations in marmosets. This study provides novel insights by using scalp EEG to capture widespread neural representations in marmosets during vocal perception, filling gaps in existing knowledge.

Comparison of non-invasive, scalp-recorded auditory steady-state responses in humans, rhesus monkeys, and common marmosets.

Auditory steady-state responses (ASSRs) are basic neural responses used to probe the ability of auditory circuits to produce synchronous activity to repetitive external stimulation. Reduced ASSR has been observed in patients with schizophrenia, especially at 40 Hz. Although ASSR is a translatable biomarker with a potential both in animal models and patients with schizophrenia, little is known about the features of ASSR in monkeys. Herein, we recorded the ASSR from humans, rhesus monkeys, and marmosets using the same method to directly compare the characteristics of ASSRs among the species. We used auditory trains on a wide range of frequencies to investigate the suitable frequency for ASSRs induction, because monkeys usually use stimulus frequency ranges different from humans for vocalization. We found that monkeys and marmosets also show auditory event-related potentials and phase-locking activity in gamma-frequency trains, although the optimal frequency with the best synchronization differed among these species. These results suggest that the ASSR could be a useful translational, cross-species biomarker to examine the generation of gamma-band synchronization in nonhuman primate models of schizophrenia.

Effect of dopamine receptor-related compounds on naïve common marmosets for auditory steady-state response.

Abnormalities of auditory steady-state responses (ASSRs) and the effects of antipsychotic drugs on ASSRs have been investigated in patients with schizophrenia. It is presumed that drugs do not directly affect ASSRs because its abnormalities are associated with schizophrenia. Therefore, to investigate the direct effect of drugs on ASSRs, we established an ASSR evaluation system for common marmosets in a naïve state. Dopamine D1 receptor stimulation (SKF-81297, 2 mg/kg ip) significantly increased evoked power (EP) at 40 Hz. The phase locking factor (PLF) was increased significantly at 20, 30, 40, and 80 Hz. However, administration of a dopamine D1 receptor antagonist (SCH-39166, 0.3 mg/kg ip) resulted in a significant decrease in EP and PLF at 30 Hz. Dopamine D2 receptor stimulation (quinpirole, 1 mg/kg im) tended to increase EP and induced power (IP) at all frequencies, and a significant difference was observed at 30 Hz IP. There was no change in PLF at all frequencies. In addition, dopamine D2 receptor blockade (raclopride, 3 mg/kg ip) reduced EP and PLF at 30 Hz. Subcutaneous administration of the serotonin dopamine antagonist, risperidone (0.3 mg/kg), tended to increase IP and decrease PLF, but not significantly. Taken together, it is possible to compare the differences in the mode of action of drugs on ASSRs using naïve nonhuman primates.NEW & NOTEWORTHY We measured the effects of dopamine receptor-related compounds on ASSR in marmosets. D1 receptor stimulation increased the phase locking factor (PLF) and evoked power (EP), and reduced the induced power (IP). D2 receptor stimulation increased the IP. D1 and D2 receptor blockers reduced the PLF and EP at 30 Hz. Different modes of action of various drugs related to psychiatric disorders were evaluated by administering antipsychotic drugs to naïve marmosets.

Cerebral cortical processing time is elongated in human brain evolution.

An increase in number of neurons is presumed to underlie the enhancement of cognitive abilities in brain evolution. The evolution of human cognition is then expected to have accompanied a prolongation of net neural-processing time due to the accumulation of processing time of individual neurons over an expanded number of neurons. Here, we confirmed this prediction and quantified the amount of prolongation in vivo, using noninvasive measurements of brain responses to sounds in unanesthetized human and nonhuman primates. Latencies of the N1 component of auditory-evoked potentials recorded from the scalp were approximately 40, 50, 60, and 100 ms for the common marmoset, rhesus monkey, chimpanzee, and human, respectively. Importantly, the prominent increase in human N1 latency could not be explained by the physical lengthening of the auditory pathway, and therefore reflected an extended dwell time for auditory cortical processing. A longer time window for auditory cortical processing is advantageous for analyzing time-varying acoustic stimuli, such as those important for speech perception. A novel hypothesis concerning human brain evolution then emerges: the increase in cortical neuronal number widened the timescale of sensory cortical processing, the benefits of which outweighed the disadvantage of slow cognition and reaction.

Noninvasive scalp recording of the middle latency responses and cortical auditory evoked potentials in the alert common marmoset.

The common marmoset (Callithrix jacchus), a New World monkey, serves as a useful animal model in clinical and basic neuroscience. The present study recorded scalp auditory evoked potentials (AEP) in non-sedated common marmoset monkeys (n = 4) using a noninvasive method similar to that used in humans, and aimed to identify nonhuman primate correlates of the human AEP components. A pure tone stimulus was presented while electroencephalograms were recorded using up to 16 disk electrodes placed on the scalp and earlobes. Candidate homologues of two categories of the human AEP, namely, the middle latency responses (MLR; Na, Pa, Nb, and Pb) and the cortical auditory evoked potentials (CAEP; P1, N1, P2, N2, and the sustained potential, SP) were identified in the marmoset. These waves were labeled as CjNa, CjPa, CjNb, CjPb, CjP1, CjN1, CjP2, CjN2, and CjSP, where Cj stands for Callithrix jacchus. The last MLR component, CjPb, was identical to the first CAEP component, CjP1, similar to the relationship between Pb and P1 in humans. The peak latencies of the marmoset MLR and CAEP were generally shorter than in humans, which suggests a shorter integration time in neural processing. To our knowledge, the present study represents the first scalp recorded MLR and CAEP in the alert common marmoset. Further use of these recording methods would enable valid species comparisons of homologous brain indices between humans and animals.

Potent and Quick Responses to Conspecific Faces and Snakes in the Anterior Cingulate Cortex of Monkeys.

Appropriate processing of others' facial emotions is a fundamental ability of primates in social situations. Several moods and anxiety disorders such as depression cause a negative bias in the perception of facial emotions. Depressive patients show abnormalities of activity and gray matter volume in the perigenual portion of the anterior cingulate cortex (ACC) and an increase of activation in the amygdala. However, it is not known whether neurons in the ACC have a function in the processing of facial emotions. Furthermore, detecting predators quickly and taking avoidance behavior are important functions in a matter of life and death for wild monkeys. the existence of predators in their vicinity is life-and-death information for monkeys. In the present study, we recorded the activity of single neurons from the monkey ACC and examined the responsiveness of the ACC neurons to various visual stimuli including monkey faces, snakes, foods, and artificial objects. About one-fourth of the recorded neurons showed a significant change in activity in response to the stimuli. The ACC neurons exhibited high selectivity to certain stimuli, and more neurons exhibited the maximal response to monkey faces and snakes than to foods and objects. The responses to monkey faces and snakes were faster and stronger compared to those to foods and objects. Almost all of the neurons that responded to video stimuli responded strongly to negative facial stimuli, threats, and scream. Most of the responsive neurons were located in the cingulate gyrus or the ventral bank of the cingulate sulcus just above or anterior to the genu of the corpus callosum, that is, the perigenual portion of the ACC, which has a strong mutual connection with the amygdala. These results suggest that the perigenual portion of the ACC in addition to the amygdala processes emotional information, especially negative life-and-death information such as conspecifics' faces and snakes.

Cerebral Substrates for Controlling Rhythmic Movements.

Our daily lives are filled with rhythmic movements, such as walking, sports, and dancing, but the mechanisms by which the brain controls rhythmic movements are poorly understood. In this review, we examine the literature on neuropsychological studies of patients with focal brain lesions, and functional brain imaging studies primarily using finger-tapping tasks. These studies suggest a close connection between sensory and motor processing of rhythm, with no apparent distinction between the two functions. Thus, we conducted two functional brain imaging studies to survey the rhythm representations relatively independent of sensory and motor functions. First, we determined brain activations related to rhythm processing in a sensory modality-independent manner. Second, we examined body part-independent brain activation related to rhythm reproduction. Based on previous literature, we discuss how brain areas contribute rhythmic motor control. Furthermore, we also discuss the mechanisms by which the brain controls rhythmic movements.

Evaluation of anaesthetic and cardiorespiratory effects after intramuscular administration of alfaxalone alone, alfaxalone-ketamine and alfaxalone-butorphanol-medetomidine in common marmosets (Callithrix jacchus).

BACKGROUND: Anaesthesia is often required in common marmosets undergoing various procedures. The aim of this study was to evaluate anaesthetic and cardiopulmonary effects of alfaxalone, alfaxalone-ketamine and alfaxalone-butorphanol-medetomidine in common marmosets. METHODS: The following treatments were repeatedly administered to seven female common marmosets: Treatment A, alfaxalone (12 mg kg-1 ) alone; treatment AK, alfaxalone (1 mg animal-1 ) plus ketamine (2.5 mg animal-1 ); treatment AMB, alfaxalone (4 mg kg-1 ), medetomidine (50 µg kg-1 ) plus butorphanol (0.3 mg kg-1 ); and treatment AMB-Ati, AMB with atipamezole at 45 minutes. RESULTS AND CONCLUSIONS: Marmosets became laterally recumbent and unresponsive for approximately 30 minutes in A and AK and for approximately 60 minutes in AMB. The animals showed rapid recovery following atipamezole injection in AMB-Ati. The decrease in heart rate and SpO2 was significantly greater in AMB compared to A and AK. Oxygen supplementation, anaesthetic monitors and atipamezole should be available especially when AMB is administered.

Laminar Pattern of Projections Indicates the Hierarchical Organization of the Anterior Cingulate-Temporal Lobe Emotion System.

The anterior cingulate cortex (ACC), surrounding the genu of the corpus callosum, plays important roles in emotional processing and is functionally divided into the dorsal, perigenual, and subgenual subregions (dACC, pgACC, and sgACC, respectively). Previous studies have suggested that the pgACC and sgACC have distinctive roles in the regulation of emotion. In order to elicit appropriate emotional responses, these ACC regions require sensory information from the environment. Anatomically, the ACC has rich connections with the temporal lobe, where the higher-order processing of sensory information takes place. To clarify the organization of sensory inputs into the ACC subregions, we injected neuronal tracers into the pgACC, sgACC, and dACC and compared the afferent connections. Previously, we analyzed the afferent projections from the amygdala and found a distinct pattern for the sgACC. In the present study, the patterns of the afferent projections were analyzed in the temporal cortex, especially the temporal pole (TP) and medial temporal areas. After tracers were injected into the sgACC, we observed labeled neurons in the TP and the subiculum of the hippocampal formation. The majority of the labeled cell bodies were found in the superficial layers of the TP ("feedforward" type projections). The pgACC received afferent projections from the TP, the entorhinal cortex (EC), and the parahippocampal cortex (PHC), but not from the hippocampus. In each area, the labeled cells were mainly found in the deep layers ("feedback" type projection). The pattern for the dACC was similar to that for the pgACC. Previous studies suggested that the pgACC, but not the sgACC receive projections from the dorsolateral prefrontal cortex (DLPFC). These data suggest that the sgACC plays crucial roles for emotional responses based on sensory and mnemonic inputs from the anterior temporal lobe, whereas the pgACC is more related to the cognitive control of emotion.

Evolutionary Elongation of the Time Window of Integration in Auditory Cortex: Macaque vs. Human Comparison of the Effects of Sound Duration on Auditory Evoked Potentials.

The auditory cortex integrates auditory information over time to obtain neural representations of sound events, the time scale of which critically affects perception. This work investigated the species differences in the time scale of integration by comparing humans and monkeys regarding how their scalp-recorded cortical auditory evoked potentials (CAEPs) decrease in amplitude as stimulus duration is shortened from 100 ms (or longer) to 2 ms. Cortical circuits tuned to processing sounds at short time scales would continue to produce large CAEPs to brief sounds whereas those tuned to longer time scales would produce diminished responses. Four peaks were identified in the CAEPs and labeled P1, N1, P2, and N2 in humans and mP1, mN1, mP2, and mN2 in monkeys. In humans, the N1 diminished in amplitude as sound duration was decreased, consistent with the previously described temporal integration window of N1 (>50 ms). In macaques, by contrast, the mN1 was unaffected by sound duration, and it was clearly elicited by even the briefest sounds. Brief sounds also elicited significant mN2 in the macaque, but not the human N2. Regarding earlier latencies, both P1 (humans) and mP1 (macaques) were elicited at their full amplitudes even by the briefest sounds. These findings suggest an elongation of the time scale of late stages of human auditory cortical processing, as reflected by N1/mN1 and later CAEP components. Longer time scales of integration would allow neural representations of complex auditory features that characterize speech and music.

Blockade of dopamine D1 receptors, but not D2 receptors, decreases motivation in a novel effort-discounting paradigm in common marmosets.

Effort-based decision-making paradigms have recently been used to measure motivation in healthy subjects and patients with neuropsychiatric disorders. In the present study, we developed a novel effort-discounting paradigm using a touch-panel system in common marmosets. Marmosets were trained to choose between a low-reward (a piece of cake) requiring low-effort (one touch response) versus high-reward (three pieces of cake) requiring one of three different effort levels (one, two, or four touch responses). Because the number of trials per session was kept constant, the selection of the high-reward choice was always the optimal strategy to receive the maximum number of rewards. Marmosets' high-reward rates were reduced as the physical effort requirement was increased, when they were tested using effort discounting in either ascending or descending order of effort intensity. It indicates that marmosets' decisions could be attributable to cost-benefit evaluation, but not to their fatigue or satisfaction with the reward during the progression of the paradigm. The high dose of dopamine D1 receptor antagonist SCH-39166 (0.03 mg/kg) reduced the high-reward choice rate, only when more effort was required to obtain the high-reward than the low-reward. On the other hand, the D2 receptor antagonist raclopride (0.01 and 0.03 mg/kg) unexpectedly did not affect the high-reward choice rate, but the high dose did increase omission rate. Our finding suggests that dopamine D1 receptor signaling may play a more important role in effort-based decision making than D2 receptor signaling in marmosets. Our novel behavioral paradigm would be useful in translational research focused on motivational deficits. (PsycINFO Database Record (c) 2018 APA, all rights reserved).

Afferent connections of the dorsal, perigenual, and subgenual anterior cingulate cortices of the monkey: Amygdalar inputs and intrinsic connections.

The anterior cingulate cortex (ACC) is crucial for emotional processing, and its abnormal activities contributes to mood disorders. The ACC is divided into three subregions: the dorsal ACC (dACC), perigenual ACC (pgACC), and subgenual ACC (sgACC). Although these regions have been implicated in emotional processing, the dACC is more involved in cognitive functions, while the other two regions are important in the pathophysiology underlying mood disorders. Recent studies have suggested that the sgACC and pgACC exhibit opposite emotion-related activity patterns and that an interaction of the ACC with the amygdala is crucial for emotion-related ACC functions. Here, we injected neuronal tracers into the sgACC, pgACC, and dACC of macaques and quantitatively compared the distributions of the retrogradely labeled neurons in the amygdalar nuclei. For both the dACC and pgACC, about 90% of the labeled neurons were found in the basal nucleus, about 10% were in the accessory basal nucleus, and the lateral nucleus had almost no neuronal labeling. However, after sgACC injections, nearly half of the labeled neurons were found in the accessory basal nucleus, and a moderate number of labeled neurons were found in the lateral nucleus. These differences in amygdalar inputs might underlie the functional differences in the sgACC and pgACC. Moreover, after tracer injections in the sgACC, labeled neurons were observed in the pgACC and not the dACC, suggesting that the pgACC directly influences the activity of the sgACC.

An eye tracking system for monitoring face scanning patterns reveals the enhancing effect of oxytocin on eye contact in common marmosets.

Eye tracking systems are used to investigate eyes position and gaze patterns presumed as eye contact in humans. Eye contact is a useful biomarker of social communication and known to be deficient in patients with autism spectrum disorders (ASDs). Interestingly, the same eye tracking systems have been used to directly compare face scanning patterns in some non-human primates to those in human. Thus, eye tracking is expected to be a useful translational technique for investigating not only social attention and visual interest, but also the effects of psychiatric drugs, such as oxytocin, a neuropeptide that regulates social behavior. In this study, we report on a newly established method for eye tracking in common marmosets as unique New World primates that, like humans, use eye contact as a mean of communication. Our investigation was aimed at characterizing these primates face scanning patterns and evaluating the effects of oxytocin on their eye contact behavior. We found that normal common marmosets spend more time viewing the eyes region in common marmoset's picture than the mouth region or a scrambled picture. In oxytocin experiment, the change in eyes/face ratio was significantly greater in the oxytocin group than in the vehicle group. Moreover, oxytocin-induced increase in the change in eyes/face ratio was completely blocked by the oxytocin receptor antagonist L-368,899. These results indicate that eye tracking in common marmosets may be useful for evaluating drug candidates targeting psychiatric conditions, especially ASDs.

Hypoxemia after single-shot anesthesia in common marmosets.

BACKGROUND: It remains unknown how single-shot anesthesia influences physical parameters, especially respiratory function and blood oxygen level of common marmosets (Callithrix jacchus) which came to be used for laboratory research. METHODS: We measured blood oxygen levels, both before and after oxygenation, in 13 common marmosets under two single-shot anesthesia conditions: ketamine/xylazine/atropine and alphaxalone. RESULTS AND CONCLUSIONS: We found that SpO2 values decreased to about 80% in the ketamine/xylazine/atropine protocol and fell just below 90% in the alphaxalone protocol. We observed a clear decrease in PaO2 values under the anesthetized condition compared to the awake condition. Our data indicate that single-shot anesthesia may cause hypoxemia in marmosets. Previous studies on other non-human primate have reported no SpO2 decrease and hypoxemia; thus, our experiment suggests that marmosets may have a more fragile respiratory system and require intensive veterinary care during anesthesia.

Noninvasive scalp recording of cortical auditory evoked potentials in the alert macaque monkey.

Scalp-recorded evoked potentials (EP) provide researchers and clinicians with irreplaceable means for recording stimulus-related neural activities in the human brain, due to its high temporal resolution, handiness, and, perhaps more importantly, non-invasiveness. This work recorded the scalp cortical auditory EP (CAEP) in unanesthetized monkeys by using methods that are essentially identical to those applied to humans. Young adult rhesus monkeys (Macaca mulatta, 5-7 years old) were seated in a monkey chair, and their head movements were partially restricted by polystyrene blocks and tension poles placed around their head. Individual electrodes were fixated on their scalp using collodion according to the 10-20 system. Pure tone stimuli were presented while electroencephalograms were recorded from up to nineteen channels, including an electrooculogram channel. In all monkeys (n = 3), the recorded CAEP comprised a series of positive and negative deflections, labeled here as macaque P1 (mP1), macaque N1 (mN1), macaque P2 (mP2), and macaque N2 (mN2), and these transient responses to sound onset were followed by a sustained potential that continued for the duration of the sound, labeled the macaque sustained potential (mSP). mP1, mN2 and mSP were the prominent responses, and they had maximal amplitudes over frontal/central midline electrode sites, consistent with generators in auditory cortices. The study represents the first noninvasive scalp recording of CAEP in alert rhesus monkeys, to our knowledge.

Temporal and Motor Representation of Rhythm in Fronto-Parietal Cortical Areas: An fMRI Study.

When sounds occur with temporally structured patterns, we can feel a rhythm. To memorize a rhythm, perception of its temporal patterns and organization of them into a hierarchically structured sequence are necessary. On the other hand, rhythm perception can often cause unintentional body movements. Thus, we hypothesized that rhythm information can be manifested in two different ways; temporal and motor representations. The motor representation depends on effectors, such as the finger or foot, whereas the temporal representation is effector-independent. We tested our hypothesis with a working memory paradigm to elucidate neuronal correlates of temporal or motor representation of rhythm and to reveal the neural networks associated with these representations. We measured brain activity by fMRI while participants memorized rhythms and reproduced them by tapping with the right finger, left finger, or foot, or by articulation. The right inferior frontal gyrus and the inferior parietal lobule exhibited significant effector-independent activations during encoding and retrieval of rhythm information, whereas the left inferior parietal lobule and supplementary motor area (SMA) showed effector-dependent activations during retrieval. These results suggest that temporal sequences of rhythm are probably represented in the right fronto-parietal network, whereas motor sequences of rhythm can be represented in the SMA-parietal network.

Effects of lurasidone on ketamine-induced joint visual attention dysfunction as a possible disease model of autism spectrum disorders in common marmosets.

Infants with autism have difficulties performing joint visual attention (JVA), defined as following another person's pointing gesture and gaze. Some non-human primates (NHPs) can also perform JVA. Most preclinical research on autism spectrum disorders (ASD) has used rodents as animal models of this social interaction disorder. However, models using rodents fail to capture the complexity of social interactions that are disrupted in ASD. Therefore, JVA impairment in NHPs might be a more useful model of ASD. The aim of this study was to develop an appropriate and convenient ASD model with common marmosets. We first tested whether marmosets were capable of performing JVA. Subsequently, we administered ketamine, an N-methyl-d-aspartate (NMDA) receptor antagonist, to induce JVA impairment and investigated the effects of lurasidone, a newer antipsychotic agent, on the JVA impairments. An apparatus was constructed using 4 white boxes, which were attached to the corners of a frame. All boxes had a hinged door, and marmosets could easily obtain a reward by pushing the door. An experimenter pointed and gazed at the boxes to inform the marmosets which box contained the reward. Their behavior was scored according to the number of incorrect choices. The JVA score was significantly higher in the cued vs. uncued tasks. Ketamine significantly decreased the JVA score, but lurasidone significantly reversed this effect. These findings suggest that this experimental system could be a useful animal model of neuropsychiatric disorders characterized by NMDA-receptor signaling, including ASD, and that lurasidone might be effective for some aspects of ASD.

Rhythm information represented in the fronto-parieto-cerebellar motor system.

Rhythm is an essential element of human culture, particularly in language and music. To acquire language or music, we have to perceive the sensory inputs, organize them into structured sequences as rhythms, actively hold the rhythm information in mind, and use the information when we reproduce or mimic the same rhythm. Previous brain imaging studies have elucidated brain regions related to the perception and production of rhythms. However, the neural substrates involved in the working memory of rhythm remain unclear. In addition, little is known about the processing of rhythm information from non-auditory inputs (visual or tactile). Therefore, we measured brain activity by functional magnetic resonance imaging while healthy subjects memorized and reproduced auditory and visual rhythmic information. The inferior parietal lobule, inferior frontal gyrus, supplementary motor area, and cerebellum exhibited significant activations during both encoding and retrieving rhythm information. In addition, most of these areas exhibited significant activation also during the maintenance of rhythm information. All of these regions functioned in the processing of auditory and visual rhythms. The bilateral inferior parietal lobule, inferior frontal gyrus, supplementary motor area, and cerebellum are thought to be essential for motor control. When we listen to a certain rhythm, we are often stimulated to move our body, which suggests the existence of a strong interaction between rhythm processing and the motor system. Here, we propose that rhythm information may be represented and retained as information about bodily movements in the supra-modal motor brain system.

The influence of tempo upon the rhythmic motor control in macaque monkeys.

We examined behavioral features of isochronous repetitive movements in two macaques. The monkeys were required to press a button repetitively in response to external cues. If the cue-intervals were constant (isochronous) and sub-second, the reaction time was shorter than in random-interval condition. In contrast, in the supra-second isochronous conditions, the reaction time was not different from random-interval condition. The results suggest that the monkeys can acquire isochronous rhythms if the intervals are sub-second, probably depending on the automatic timing system. However, the conscious timing system for supra-second intervals is not well developed in monkeys, unlike humans.