Evolutionary loss of complexity in human vocal anatomy as an adaptation for speech

Human speech production obeys the same acoustic principles as vocal production in other animals but has distinctive features: A stable vocal source is filtered by rapidly changing formant frequencies. To understand speech evolution, we examined a wide range of primates, combining observations of phonation with mathematical modeling. We found that source stability relies upon simplifications in laryngeal anatomy, specifically the loss of air sacs and vocal membranes. We conclude that the evolutionary loss of vocal membranes allows human speech to mostly avoid the spontaneous nonlinear phenomena and acoustic chaos common in other primate vocalizations. This loss allows our larynx to produce stable, harmonic-rich phonation, ideally highlighting formant changes that convey most phonetic information. Paradoxically, the increased complexity of human spoken language thus followed simplification of our laryngeal anatomy.</jats:p

A Neural Correlate of the Processing of Multi-Second Time Intervals in Primate Prefrontal Cortex

Several areas of the brain are known to participate in temporal processing. Neurons in the prefrontal cortex (PFC) are thought to contribute to perception of time intervals. However, it remains unclear whether the PFC itself can generate time intervals independently of external stimuli. Here we describe a group of PFC neurons in area 9 that became active when monkeys recognized a particular elapsed time within the range of 1–7 seconds. Another group of area 9 neurons became active only when subjects reproduced a specific interval without external cues. Both types of neurons were individually tuned to recognize or reproduce particular intervals. Moreover, the injection of muscimol, a GABA agonist, into this area bilaterally resulted in an increase in the error rate during time interval reproduction. These results suggest that area 9 may process multi-second intervals not only in perceptual recognition, but also in internal generation of time intervals

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

Responses of monkey prefrontal neurons during the execution of transverse patterning

Recent functional imaging studies have suggested that the prefrontal cortex (PF) is engaged in the performance of transverse patterning (TP), which consists of 3 conflicting discriminations (A+/B−, B+/C−, C+/A−). However, the roles of PF in TP are still unclear. To address this issue, we examined the neuronal responses in 3 regions [the principal sulcus (PS), dorsal convexity (DC), and medial prefrontal cortex (MPF)] of the macaque PF during the performance of an oculomotor version of TP. A delayed matching-to-sample (DMS) task was used as a control task. The TP task-responsive neurons were most abundant in MPF. We analyzed the dependency of each neuronal response on the task type (TP or DMS), target shape (A, B, or C), and target location (left or right). Immediately after the choice cue presentation, many MPF neurons showed task dependency. Interestingly, some of them already exhibited differential activity between the 2 tasks before the choice cue presentation. Immediately before the saccade, the number of target location-dependent neurons increased in MPF and PS. Among them, many MPF neurons were also influenced by the task type, whereas PS neurons tended to show location dependency without task dependency. These results suggest that MPF and PS are involved in the execution of TP: MPF appears to be more important in the target selection based on the TP rule, whereas PS is apparently more related to the response preparation. In addition, some neurons showed a postsaccadic response, which may be related to the feedback mechanism

Multisynaptic projections from the ventrolateral prefrontal cortex to hand and mouth representations of the monkey primary motor cortex.

Different sectors of the prefrontal cortex have distinct neuronal connections with higher-order sensory areas and/or limbic structures and are related to diverse aspects of cognitive functions, such as visual working memory and reward-based decision-making. Recent studies have revealed that the prefrontal cortex (PF), especially the lateral PF, is also involved in motor control. Hence, different sectors of the PF may contribute to motor behaviors with distinct body parts. To test this hypothesis anatomically, we examined the patterns of multisynaptic projections from the PF to regions of the primary motor cortex (MI) that represent the arm, hand, and mouth, using retrograde transsynaptic transport of rabies virus. Four days after rabies injections into the hand or mouth region, particularly dense neuron labeling was observed in the ventrolateral PF, including the convexity part of ventral area 46. After the rabies injections into the mouth region, another dense cluster of labeled neurons was seen in the orbitofrontal cortex (area 13). By contrast, rabies labeling of PF neurons was rather sparse in the arm-injection cases. The present results suggest that the PF-MI multisynaptic projections may be organized such that the MI hand and mouth regions preferentially receive cognitive information for execution of elaborate motor actions

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

Recruitment of calbindin into nigral dopamine neurons protects against MPTP-Induced parkinsonism.

BACKGROUND:Parkinson\u27s disease is caused by dopamine deficiency in the striatum, which is a result of loss of dopamine neurons from the substantia nigra pars compacta. There is a consensus that a subpopulation of nigral dopamine neurons that expresses the calcium-binding protein calbindin is selectively invulnerable to parkinsonian insults. The objective of the present study was to test the hypothesis that dopamine neuron degeneration might be prevented by viral vector-mediated gene delivery of calbindin into the dopamine neurons that do not normally contain it.METHODS:A calbindin-expressing adenoviral vector was injected into the striatum of macaque monkeys to be conveyed to cell bodies of nigral dopamine neurons through retrograde axonal transport, or the calbindin-expressing lentiviral vector was injected into the nigra directly because of its predominant uptake from cell bodies and dendrites. The animals in which calbindin was successfully recruited into nigral dopamine neurons were administered systemically with MPTP.RESULTS:In the monkeys that had received unilateral vector injections, parkinsonian motor deficits, such as muscular rigidity and akinesia/bradykinesia, appeared predominantly in the limbs corresponding to the non-calbindin-recruited hemisphere after MPTP administration. Data obtained from tyrosine hydroxylase immunostaining and PET imaging for the dopamine transporter revealed that the nigrostriatal dopamine system was preserved better on the calbindin-recruited side. Conversely, on the non-calbindin-recruited control side, many more dopamine neurons expressed α-synuclein.CONCLUSIONS:The present results indicate that calbindin recruitment into nigral dopamine neurons protects against the onset of parkinsonian insults, thus providing a novel approach to PD prevention