Effects of tegmental lesions on the isolation call of squirrel monkeys

Midbrain neurons important for the production of mouse ultrasonic vocalizations are not required for distress calls

A fundamental feature of vocal communication is that animals produce vocalizations with different acoustic features in different behavioral contexts (contact calls, territorial calls, courtship calls, etc.). The midbrain periaqueductal gray (PAG) is a key region that regulates vocal production, and artificial activation of the PAG can elicit the production of multiple species-typical vocalization types.1,2,3,4,5,6,7,8,9 How PAG circuits are organized to regulate the production of different vocalization types remains unknown. On the one hand, studies have found that partial PAG lesions abolish the production of some vocalization types while leaving others intact,3,8,10,11 suggesting that different populations of PAG neurons might control the production of different vocalization types. On the other hand, electrophysiological recordings have revealed individual PAG neurons that increase their activity during the production of multiple vocalization types,12,13,14 suggesting that some PAG neurons may regulate the production of more than one vocalization type. To test whether a single population of midbrain neurons regulates the production of different vocalization types, we applied intersectional methods to selectively ablate a population of midbrain neurons important for the production of ultrasonic vocalizations (USVs) in mice. We find that, although ablation of these PAG-USV neurons blocks USV production in both males and females, these neurons are not required for the production of distress calls. Our findings suggest that distinct populations of midbrain neurons control the production of different vocalization types.

Isolation-induced vocalization in the infant rat depends on the nucleus accumbens

Mammalian infants vocalize when socially isolated. Vocalization guides the return of the caregiver and thereby maintains an environment critical to the infant's survival. Although the role of the periaqueductal gray area (PAG) in these vocalizations is established, other aspects of the relevant neural circuitry remain under-studied. Here we report that output from the nucleus accumbens (Acb) is necessary for isolation-induced vocalizations of infant rats aged postnatal days (PND) 11-13. Local inhibition via infusion of the GABA_A agonist muscimol (.8 μg/side) of the Acb, but not the dorsolateral striatum, blocked isolation-induced vocalizations, independent of whether the isolation was at room temperature, followed a brief reunion with the dam, or occurred in a cool (10 °C) environment. These findings highlight a possible anatomical area mediating the mammalian infant response to social separation and, more generally, to the development of social attachment.

Brain organization for language from the perspective of electrical stimulation mapping

A model for the organization of language in the adult humans brain is derived from electrical stimulation mapping of several language-related functions: naming, reading, short-term verbal memory, mimicry of orofacial movements, and phoneme identification during neurosurgical operations under local anesthesia. A common peri-Sylvian cortex for motor and language functions is identified in the language dominant hemisphere, including sites common to sequencing of movements and identification of phonemes that may represent an anatomic substrate for the “motor theory of speech perception.” This is surrounded by sites related to short-term verbal memory, with sites specialized for such language functions as naming or syntax at the interface between these motor and memory areas. Language functions are discretely and differentially localized in association cortex, including some differential localization of the same function, naming, in multiple languages. There is substantial individual variability in the exact location of sites related to a particular function, a variability which can be partly related to the patient's sex and overall language ability and which may depend on prior brain injury and, perhaps subtly, on prior experience. A common “specific alerting response” mechanism for motor and language functions is identified in the lateral thalamus of the language–dominant hemisphere, a mechanism that may select the cortical areas appropriate for a particular language function.

Neural circuits underlying crying and cry responding in mammals

Crying is a universal vocalization in human infants, as well as in the infants of other mammals. Little is known about the neural structures underlying cry production, or the circuitry that mediates a caregiver's response to cry sounds. In this review, the specific structures known or suspected to be involved in this circuit are identified, along with neurochemical systems and hormones for which evidence suggests a role in responding to infants and infant cries. In addition, evidence that crying elicits parental responses in different mammals is presented. An argument is made for including 'crying' as a functional category in the vocal repertoire of all mammalian infants (and the adults of some species). The prevailing neural model for crying production considers forebrain structures to be dispensable. However, evidence for the anterior cingulate gyrus in cry production, and this structure along with the amygdala and some other forebrain areas in responding to cries is presented.

Neuronal activity in the periaqueductal gray and bordering structures during vocal communication in the squirrel monkey

In seven freely moving squirrel monkeys (Saimiri sciureus), the neuronal activity in the periaqueductal gray (PAG) and bordering structures was registered during vocal communication, using a telemetric single-unit recording technique. In 9.3% of the PAG neurons, a vocalization-correlated activity was found. Four reaction types could be distinguished: a) neurons, showing an activity burst immediately before vocalization onset; b) neurons, firing during vocalization, and starting shortly before vocalization onset; c) neurons, firing exclusively during vocalization; d) neurons, firing in the interval between perceived vocalizations (i.e. vocalizations produced by group mates) and self-produced vocal response. All PAG neurons showed a marked vocalization-type specificity. None of the neurons reflected simple acoustic parameters, such as fundamental frequency or amplitude, in its discharge rate. None of the neurons reacted to vocalizations of other animals not responded to by the experimental animal. All four reaction types found in the PAG were also found in the reticular formation bordering the PAG, though in lower density.

Vocal communication and the triune brain

This paper tests the 'fit' between Paul MacLean's triune brain scheme of brain organization and existing knowledge about the pathways mediating vocal communication in mammals. One component of MacLean's limbic system ('paleomammalian brain'), the 'thalamocingulate circuit,' is found to have an important role in expression of vocalizations, particularly the 'isolation call' (such as are given by mammalian infants when distressed or separated from their caregivers). Recent evidence suggests that this circuit may also have a role in perception of infant cries in humans. Outside of this circuit, the triune brain model has little to offer in the way of insights into how the brain is organized to mediate vocal communication. There is little evidence that the striatal complex ('R-complex' or 'protoreptilian formation') is involved in any major way in vocal communication, although it appears to be involved in some visual displays in both reptiles and nonhuman primates. Interestingly, components of the reptilian brain may be involved in human speech production, and avian homologues involved in birdsong. The neocortex ('neomammalian formation') has well-known importance in speech production and perception, but little evidence exists for a role in vocal production in nonhuman mammals. However, cortical mechanisms do play a role in perception of vocalizations, at least in nonhuman primates. It is concluded that a set of neural structures termed the 'communication brain' mediate vocal communication in mammals, and that this model does not fit well into the triune brain scheme of brain organization.

On the nature and evolution of the neural bases of human language

The traditional theory equating the brain bases of language with Broca's and Wernicke's neocortical areas is wrong. Neural circuits linking activity in anatomically segregated populations of neurons in subcortical structures and the neocortex throughout the human brain regulate complex behaviors such as walking, talking, and comprehending the meaning of sentences. When we hear or read a word, neural structures involved in the perception or real-world associations of the word are activated as well as posterior cortical regions adjacent to Wernicke's area. Many areas of the neocortex and subcortical structures support the cortical-striatal-cortical circuits that confer complex syntactic ability, speech production, and a large vocabulary. However, many of these structures also form part of the neural circuits regulating other aspects of behavior. For example, the basal ganglia, which regulate motor control, are also crucial elements in the circuits that confer human linguistic ability and abstract reasoning. The cerebellum, traditionally associated with motor control, is active in motor learning. The basal ganglia are also key elements in reward-based learning. Data from studies of Broca's aphasia, Parkinson's disease, hypoxia, focal brain damage, and a genetically transmitted brain anomaly (the putative "language gene," family KE), and from comparative studies of the brains and behavior of other species, demonstrate that the basal ganglia sequence the discrete elements that constitute a complete motor act, syntactic process, or thought process. Imaging studies of intact human subjects and electrophysiologic and tracer studies of the brains and behavior of other species confirm these findings. As Dobzansky put it, "Nothing in biology makes sense except in the light of evolution" (cited in Mayr, 1982). That applies with as much force to the human brain and the neural bases of language as it does to the human foot or jaw. The converse follows: the mark of evolution on the brains of human beings and other species provides insight into the evolution of the brain bases of human language. The neural substrate that regulated motor control in the common ancestor of apes and humans most likely was modified to enhance cognitive and linguistic ability. Speech communication played a central role in this process. However, the process that ultimately resulted in the human brain may have started when our earliest hominid ancestors began to walk.

C-fos expression during vocal mobbing in the new world monkey Saguinus fuscicollis

In order to find brain areas involved in the vocal expression of emotion, we compared c-fos expression in three groups of saddle-back tamarins (Saguinus fuscicollis). One group, consisting of three animals, was made to utter more than 800 mobbing calls by electrical stimulation of the periaqueductal grey of the midbrain (PAG). A second group, consisting of two animals, was stimulated in the PAG with the same intensity and for the same duration as the first group but at sites that did not produce vocalization. These sites lay somewhat medial to the vocalization-eliciting sites. A third group, consisting of two animals, was stimulated at vocalization-eliciting sites in the PAG but with an intensity below vocalization threshold. Fos-like immunoreactivity that was found in the vocalizing but not in the non-vocalizing animals was located in the dorsomedial and ventrolateral prefrontal cortex, anterior cingulate cortex, ventrolateral premotor cortex, sensorimotor face cortex, insula, inferior parietal cortex, superior temporal cortex, claustrum, entorhinal and parahippocampal cortex, basal amygdaloid nucleus, anterior and dorsomedial hypothalamus, nucleus reuniens, lateral habenula, Edinger-Westphal nucleus, ventral and dorsolateral midbrain tegmentum, nucleus cuneiformis, sagulum, pedunculopontine and laterodorsal tegmental nuclei, ventral raphe, periambigual reticular formation and solitary tract nucleus. For some of these structures (e.g. anterior cingulate cortex and periambigual reticular formation), there is evidence also from electrical stimulation, lesioning and single-unit recording studies that they are involved in vocal control. For other structures (e.g. lateral habenula, Edinger-Westphal nucleus), the available evidence speaks against such a role. Fos activation in these cases is probably related to non-vocal reactions accompanying the electrically elicited vocalizations. A third group of structures consists of areas for which a role in vocal control cannot be excluded but for which the present study presents the first evidence for such a role (e.g. claustrum and sagulum). These structures deserve further studies using more specific methods.

The role of the periaqueductal grey in vocal behaviour

This is a review of our current knowledge about the role of the periaqueductal grey (PAG) in vocal control. It shows that electrical stimulation of the PAG can evoke species-specific calls with short latency and low habituation in many mammals. The vocalization-eliciting region contains neurones the activity of which is correlated with the activity of specific laryngeal muscles. Lesioning studies show that destruction of the PAG and laterally bordering tegmentum can cause mutism without akinesia. Neuroanatomical studies reveal that the PAG lacks direct connections with the majority of phonatory motoneurone pools but is connected with the periambigual reticular formation, an area which does have direct connections with all phonatory motor nuclei. The PAG receives a glutamatergic input from several sensory areas, such as the superior and inferior colliculi, solitary tract nucleus and spinal trigeminal nucleus. Glutamatergic input, in addition, reaches it from numerous limbic structures the stimulation of which also produces vocalization, such as the anterior cingulate cortex, septum, amygdala, hypothalamus and midline thalamus. Pharmacological blocking of this glutamatergic input causes mutism. The glutamatceptive vocalization-controlling neurones are under a tonic inhibitory control from GABAergic neurones. Removal of this inhibitory input lowers the threshold for the elicitation of vocalization by external stimuli. A modulatory control on vocalization threshold is also exerted by glycinergic, opioidergic, cholinergic, histaminergic and, possibly, noradrenergic and dopaminergic afferents. It is proposed that the PAG serves as a link between sensory and motivation-controlling structures on the one hand and the periambigual reticular formation coordinating the activity of the different phonatory muscles on the other.

Gender differences in reactivity of adult squirrel monkeys to short-term environmental challenges

Evidence is presented to show that individual adult squirrel monkeys show gender-specific reactivity profiles to threatening stimuli under laboratory conditions, and that a putative anxiogenic drug, benactyzine hydrochloride, enhances the vocal response to threatening stimuli, but otherwise preserves the relative importance of the stimuli to both males and females. These data support the conclusion that screening of putative anxiolytic drugs in a primate model can be accomplished using efficient, ethologically based testing procedures in the laboratory.

Role of midline frontolimbic cortex in production of the isolation call of squirrel monkeys

Since the separation cry of mammals serves to maintain (1) mother-offspring contact and (2) contact between members of a group, it probably ranks as a basic mammalian vocalization. The present study is part of an investigation concerned with identifying the cerebral representation of the separation call in squirrel monkeys. For this purpose, monkeys are tested for their ability to produce spontaneous calls in isolation before and after ablations of different parts of the brain. Because of the subject's auditory and visual isolation, the call emitted during testing is referred to as the isolation call. In a preceding study, it was shown that lesions at the thalamomidbrain junction and in the ventral central gray interfere with the structure and/or production of the call. The present study focuses on the rostral midline limbic cortex, known to be one of the two cortical areas where stimulation elicits vocalization in monkeys. Evidence derived by the process of elimination indicates that the spontaneous call depends on the concerted action of a continuous band of rostral limbic cortex comprising parts of areas 24, 25, and 12. The midline frontal neocortex peripheral to this limbic zone does not appear to be essential for the call.

Neuronal activity in the ventral tegmental area (VTA) during motivated bar press feeding in the monkey

Neuronal activity of 58 dopaminergic (DA) and 200 non-dopaminergic (non-DA) neurons in the ventral tegmental area (VTA) of female monkeys was recorded, and correlation to bar press feeding, sensory stimulation and change in motivation was investigated. DA neurons, judged by duration of action potentials (more than 2.5 ms) and responsiveness to apomorphine, had lower firing rates (0-8 impulses/s); non-DA neurons had intermediate firing rates (10-30 impulses/s). Two-thirds of the DA and non-DA neurons responded in bar press feeding; the former with mostly tonic and the latter with phasic responses. Fifteen neurons (5%) responded phasically to arm extension toward the bar, 124 (excitation 88, inhibition 36, 45%) during bar press (BP), and 91 (excitation 32, inhibition 59, 33%) during ingestion reward (RW). Most BP responses (84/124, 68%) continued tonically throughout the BP period with no correlation to each BP movement. In 14 neurons (14/124, 11%), firing showed a specific variation: transient early BP responses shifted to tonic steady ones in palatable food trials, and the shifts correlated well with BP speed. In 20 other neurons, firing increased during BP hip lifting, and at specific vocalization to ask for food; it decreased during food ingestion, drinking and inguino-crural stimulation. Apomorphine administration decreased firing for the first 5-15 min, then increased it with frequent lip smacking, nausea, involuntary movement and vocalization. Thus VTA neurons showed mostly steady tonic responses but some specific phasic responses. They responded not only to motor events but also in close relation to changes of motivational aspects. Neuronal responses were excitation during procurement of reward and inhibition during or after perception of reward. This modulation in firing, might be important in the initiation and execution of movement and/or motivated behavior.

Mediation of separation distress by alpha 2-adrenergic mechanisms in a non-human primate

This study provides the first behavioral evidence in support of an alpha-adrenergic mechanism underlying imipramine's amelioration of separation distress. The rate of separation-induced vocalization by adult squirrel monkeys was decreased by imipramine and the alpha 2-adrenergic agonist clonidine, and increased by the alpha 2-adrenergic antagonist yohimbine. Yohimbine, but not the alpha 1-antagonist prazosin, reversed the clonidine effect suggesting that drugs acting directly on alpha 2-receptors may have a role in management of separation anxiety.

The effects of brainstem lesions on vocalization in the squirrel monkey

The present study is an attempt to find out the brain areas involved in the motor coordination of species-specific vocalization. For this purpose, high-frequency coagulations were placed in a systematic manner throughout the brainstem and posterior diencephalon in altogether 43 squirrel monkeys (Saimiri sciureus). The effect of these lesions on different call types elicited by electrical brain stimulation was studied spectrographically. It was found that bilateral destruction of the ventrolateral, ventroposterior and intralaminar thalamus, periventricular and rostral periaqueductal gray, ventral tegmental area of Tsai, nucl. interpeduncularis, nucl. ruber, anterodorsolateral midbrain tegmentum, superior and inferior colliculi, pontine gray, cerebral peduncles, medial pontine reticular formation, raphe and vestibular nuclei did not affect the acoustic structure of the calls tested. On the other hand, lesions in the ventrolateral midbrain involving the substantia nigra and overlying reticular formation, in the midbrain tegmentum just below the inferior colliculus, in the lateral pons and almost the whole medulla (minimal lesion size: 2.5 mm3) changed vocalization significantly. It is suggested that the latter areas are more or less directly involved in the motor coordination of vocalization, while the first are not.