Neuronal Activity in the Premotor Cortex of Monkeys Reflects Both Cue Salience and Motivation for Action Generation and Inhibition.

Reward prospect weighs on motor decision processes, enhancing the selection of appropriate actions and the inhibition of others. While many studies have investigated the neuronal basis of reward representations and of cortical control of actions, the neuronal correlates of the influences of reward prospect on motor decisions are less clear. We recorded from the dorsal premotor cortex (PMd) of 2 male macaque monkeys performing a modified version of the Stop-signal (countermanding) task. This task challenges motor decisions by requiring responding to a frequent Go stimulus, but to suppress this response when a rare Stop signal is presented during the reaction time. We unbalanced the motivation to respond or to suppress the response by presenting a cue informing on three different rewards schedules: in one case, Go trials were rewarded more than Stop trials; in another case, Stop trials were rewarded more than Go trials; in the last case, both types of trials were rewarded equally. Monkeys adopted different strategies according to reward information provided by the cue: the higher the reward for Stop trials, the higher their ability to suppress the response and the slower their response to Go stimuli. PMd neuronal activity evolved in time and correlated with the behavior: PMd signaled first the cue salience, representing the chance to earn the highest reward at stake, then reflected the shaping of the motor choice by the motivation to move or to stop. These findings represent a neuronal correlate of the influence of reward information on motor decision.SIGNIFICANCE STATEMENT The motivation to obtain rewards drives how animals act over their environment. To explore the involvement of motor cortices in motivated behaviors, we recorded high-resolution neuronal activity in the premotor cortex of monkeys performing a task that manipulated the motivation to generate/withhold a movement through different cued reward probabilities. Our results show the presence of neuronal signals dynamically reflecting the salience of the cue, in the time immediately following its presentation, and a motivation-related activity in performing (or cancelling) a motor program, while the behavioral response approached. The encoding of multiple reward-related signals in this region leads to consider an important role of premotor areas in the reward circuitry supporting action.

Neuronal dynamics of signal selective motor plan cancellation in the macaque dorsal premotor cortex.

Primates adopt various strategies to interact with the environment. Yet, no study has examined the effects of behavioural strategies with regard to how movement inhibition is implemented at the neuronal level. We used a modified version of the stop-task by adding an extra signal - termed the Ignore signal - capable of influencing the inhibition of movements only within a specific strategy. We simultaneously recorded multisite neuronal activity from the dorsal premotor (PMd) cortex of macaque monkeys during the task and applied a state-space approach. As a result, we found that movement generation is characterized by neuronal dynamics that evolve between subspaces. When the movement is halted, this evolution is arrested and inverted. Conversely, when the Ignore signal is presented, inversion of the evolution is observed briefly and only when a specific behavioural strategy is adopted. Moreover, neuronal signatures during the inhibitory process were predictive of how PMd processes inhibitory signals, allowing the classification of the resulting behavioural strategy. Our data further corroborate the PMd as a critical node in movement inhibition.

Within- and between-hemifield generalization of repetition suppression in inferior temporal cortex.

The decrease in response with stimulus repetition is a common property observed in many sensory brain areas. This repetition suppression (RS) is ubiquitous in neurons of macaque inferior temporal (IT) cortex, the end-stage of the ventral visual pathway. The neural mechanisms of RS in IT are still unclear, and one possibility is that it is inherited from areas upstream to IT that show also RS. Since neurons in IT have larger receptive fields compared with earlier visual areas, we examined the inheritance hypothesis by presenting adapter and test stimuli at widely different spatial locations along both vertical and horizontal meridians and across hemifields. RS was present for distances between adapter and test stimuli up to 22° and when the two stimuli were presented in different hemifields. Also, we examined the position tolerance of the stimulus selectivity of adaptation by comparing the responses to a test stimulus following the same (repetition trial) or a different (alternation trial) adapter at a position different from the test stimulus. Stimulus-selective adaptation was still present and consistently stronger in the later phase of the response for distances up to 18°. Finally, we observed stimulus-selective adaptation in repetition trials even without a measurable excitatory response to the adapter stimulus. To accommodate these and previous data, we propose that at least part of the stimulus-selective adaptation in IT is based on short-term plasticity mechanisms within IT and/or reflects top-down activity from areas downstream to IT.NEW & NOTEWORTHY Neurons in inferior temporal cortex reduce their response when stimuli are repeated. To assess whether this repetition suppression is inherited from upstream visual areas, we examined the extent of its spatial generalization. We observed stimulus-selective adaptation when adapter and test stimuli were presented at widely different spatial positions and in different hemifields. These data suggest that at least part of the repetition suppression originates within inferior temporal cortex and/or reflects feedback from downstream areas.

An Open Resource for Non-human Primate Optogenetics.

Optogenetics has revolutionized neuroscience in small laboratory animals, but its effect on animal models more closely related to humans, such as non-human primates (NHPs), has been mixed. To make evidence-based decisions in primate optogenetics, the scientific community would benefit from a centralized database listing all attempts, successful and unsuccessful, of using optogenetics in the primate brain. We contacted members of the community to ask for their contributions to an open science initiative. As of this writing, 45 laboratories around the world contributed more than 1,000 injection experiments, including precise details regarding their methods and outcomes. Of those entries, more than half had not been published. The resource is free for everyone to consult and contribute to on the Open Science Framework website. Here we review some of the insights from this initial release of the database and discuss methodological considerations to improve the success of optogenetic experiments in NHPs.

Probing the Mechanisms of Repetition Suppression in Inferior Temporal Cortex with Optogenetics.

Neurons in macaque inferior temporal (IT) cortex show a decrease in the response with stimulus repetition, known as repetition suppression (RS). Several mechanisms may contribute to RS in IT, such as firing rate-dependent fatigue and transsynaptic mechanisms, like synaptic depression or reduced input from neurons within the same area or from up- or downstream areas. We examined the role of firing rate fatigue and transsynaptic mechanisms by stimulating directly IT neurons using optogenetics and measured the effect of photo-stimulation on their responses using timing parameters that resulted in RS for visual stimuli. Photo-stimulation of IT neurons resulted in a marginally decreased probability of spiking activity to a subsequent photo-stimulation or to a subsequent low-contrast visual stimulus. This response reduction was small relative to that for repeated visual stimuli and was related to post-stimulation inhibition of the activity during the interval between adapter and test stimuli. Presentation of a visual adapter did not change the response to subsequent photo-stimulation. In neurons whose response to the visual adapter was inhibited by simultaneous photo-stimulation, RS to visual stimuli was unaffected. Overall, these data imply that RS in IT has a transsynaptic origin, with little or no contribution of intrinsic firing rate fatigue. In addition, they suggest a limited contribution of both local synaptic depression and reduced input from nearby IT neurons, whose responses were postulated to be decreased by firing rate fatigue, to RS in IT.

De novo assembly, functional annotation, and analysis of the giant reed (Arundo donax L.) leaf transcriptome provide tools for the development of a biofuel feedstock.

BACKGROUND: Arundo donax has attracted renewed interest as a potential candidate energy crop for use in biomass-to-liquid fuel conversion processes and biorefineries. This is due to its high productivity, adaptability to marginal land conditions, and suitability for biofuel and biomaterial production. Despite its importance, the genomic resources currently available for supporting the improvement of this species are still limited. RESULTS: We used RNA sequencing (RNA-Seq) to de novo assemble and characterize the A. donax leaf transcriptome. The sequencing generated 1249 million clean reads that were assembled using single-k-mer and multi-k-mer approaches into 62,596 unique sequences (unitranscripts) with an N50 of 1134 bp. TransDecoder and Trinotate software suites were used to obtain putative coding sequences and annotate them by mapping to UniProtKB/Swiss-Prot and UniRef90 databases, searching for known transcripts, proteins, protein domains, and signal peptides. Furthermore, the unitranscripts were annotated by mapping them to the NCBI non-redundant, GO and KEGG pathway databases using Blast2GO. The transcriptome was also characterized by BLAST searches to investigate homologous transcripts of key genes involved in important metabolic pathways, such as lignin, cellulose, purine, and thiamine biosynthesis and carbon fixation. Moreover, a set of homologous transcripts of key genes involved in stomatal development and of genes coding for stress-associated proteins (SAPs) were identified. Additionally, 8364 simple sequence repeat (SSR) markers were identified and surveyed. SSRs appeared more abundant in non-coding regions (63.18%) than in coding regions (36.82%). This SSR dataset represents the first marker catalogue of A. donax. 53 SSRs (PolySSRs) were then predicted to be polymorphic between ecotype-specific assemblies, suggesting genetic variability in the studied ecotypes. CONCLUSIONS: This study provides the first publicly available leaf transcriptome for the A. donax bioenergy crop. The functional annotation and characterization of the transcriptome will be highly useful for providing insight into the molecular mechanisms underlying its extreme adaptability. The identification of homologous transcripts involved in key metabolic pathways offers a platform for directing future efforts in genetic improvement of this species. Finally, the identified SSRs will facilitate the harnessing of untapped genetic diversity. This transcriptome should be of value to ongoing functional genomics and genetic studies in this crop of paramount economic importance.

Genetic variation for leaf morphology, leaf structure and leaf carbon isotope discrimination in European populations of black poplar (Populus nigra L.).

To buffer against the high spatial and temporal heterogeneity of the riparian habitat, riparian tree species, such as black poplar (Populus nigra L.), may display a high level of genetic variation and phenotypic plasticity for functional traits. Using a multisite common garden experiment, we estimated the relative contribution of genetic and environmental effects on the phenotypic variation expressed for individual leaf area, leaf shape, leaf structure and leaf carbon isotope discrimination (Δ(13)C) in natural populations of black poplar. Twenty-four to 62 genotypes were sampled in nine metapopulations covering a latitudinal range from 48 °N to 42 °N in France and in Italy and grown in two common gardens at Orléans (ORL) and at Savigliano (SAV). In the two common gardens, substantial genetic variation was expressed for leaf traits within all metapopulations, but its expression was modulated by the environment, as attested by the genotype × environment (G × E) interaction variance being comparable to or even greater than genetic effects. For LA, G × E interactions were explained by both changes in genotype ranking between common gardens and increased variation in SAV, while these interactions were mainly attributed to changes in genotype ranking for Δ(13)C. The nine P. nigra metapopulations were highly differentiated for LA, as attested by the high coefficient of genetic differentiation (QST = 0.50 at ORL and 0.51 at SAV), and the pattern of metapopulation differentiation was highly conserved between the two common gardens. In contrast, they were moderately differentiated for Δ(13)C (QST = 0.24 at ORL and 0.25 at SAV) and the metapopulation clustering changed significantly between common gardens. Our results evidenced that the nine P. nigra metapopulations present substantial genetic variation and phenotypic plasticity for leaf traits, which both represent potentially significant determinants of populations' capacities to respond, on a short-term basis and over generations, to environmental variations.

Phenotypic plasticity, QTL mapping and genomic characterization of bud set in black poplar.

BACKGROUND: The genetic control of important adaptive traits, such as bud set, is still poorly understood in most forest trees species. Poplar is an ideal model tree to study bud set because of its indeterminate shoot growth. Thus, a full-sib family derived from an intraspecific cross of P. nigra with 162 clonally replicated progeny was used to assess the phenotypic plasticity and genetic variation of bud set in two sites of contrasting environmental conditions. RESULTS: Six crucial phenological stages of bud set were scored. Night length appeared to be the most important signal triggering the onset of growth cessation. Nevertheless, the effect of other environmental factors, such as temperature, increased during the process. Moreover, a considerable role of genotype × environment (G × E) interaction was found in all phenological stages with the lowest temperature appearing to influence the sensitivity of the most plastic genotypes.Descriptors of growth cessation and bud onset explained the largest part of phenotypic variation of the entire process. Quantitative trait loci (QTL) for these traits were detected. For the four selected traits (the onset of growth cessation (date2.5), the transition from shoot to bud (date1.5), the duration of bud formation (subproc1) and bud maturation (subproc2)) eight and sixteen QTL were mapped on the maternal and paternal map, respectively. The identified QTL, each one characterized by small or modest effect, highlighted the complex nature of traits involved in bud set process. Comparison between map location of QTL and P. trichocarpa genome sequence allowed the identification of 13 gene models, 67 bud set-related expressional and six functional candidate genes (CGs). These CGs are functionally related to relevant biological processes, environmental sensing, signaling, and cell growth and development. Some strong QTL had no obvious CGs, and hold great promise to identify unknown genes that affect bud set. CONCLUSIONS: This study provides a better understanding of the physiological and genetic dissection of bud set in poplar. The putative QTL identified will be tested for associations in P. nigra natural populations. The identified QTL and CGs will also serve as useful targets for poplar breeding.

Bud set in poplar--genetic dissection of a complex trait in natural and hybrid populations.

• The seasonal timing of growth events is crucial to tree distribution and conservation. The seasonal growth cycle is strongly adapted to the local climate that is changing because of global warming. We studied bud set as one cornerstone of the seasonal growth cycle in an integrative approach. • Bud set was dissected at the phenotypic level into several components, and phenotypic components with most genetic variation were identified. While phenotypic variation resided in the timing of growth cessation, and even so more in the duration from growth cessation to bud set, the timing of growth cessation had a stronger genetic component in both natural and hybrid populations. • Quantitative trait loci (QTL) were identified for the most discriminative phenotypic bud-set components across four poplar pedigrees. The QTL from different pedigrees were recurrently detected in six regions of the poplar genome. • These regions of 1.83-4.25 Mbp in size, containing between 202 and 394 genes, form the basis for further molecular-genetic dissection of bud set.