In vivo studies have demonstrated that the superior colliculus (SC) integrates sensory information and plays a role in controlling orienting motor output. However, how the complex microcircuitry within the SC, as documented by slice studies, subserves these functions is unclear. Optogenetics affords the potential to examine, in behaving animals, the functional roles of specific neuron types that comprise heterogeneous nuclei. As a first step toward understanding how SC microcircuitry underlies motor output, we applied optogenetics to mice performing an odor discrimination task in which sensory decisions are reported by either a leftward or rightward SC-dependent orienting movement. We unilaterally expressed either channelrhodopsin-2 or halorhodopsin in the SC and delivered light in order to excite or inhibit motor-related SC activity as the movement was planned. We found that manipulating SC activity predictably affected the direction of the selected movement in a manner that depended on the difficulty of the odor discrimination. This study demonstrates that the SC plays a similar role in directional orienting movements in mice as it does in other species, and provides a framework for future investigations into how specific SC cell types contribute to motor control.

-A fundamental goal of systems neuroscience is to understand the neural mechanisms underlying decision making. The midbrain superior colliculus (SC) is known to be central to the selection of one among many potential spatial targets for movements, which represents an important form of decision making that is tractable to rigorous experimental investigation. In this review, we first discuss data from mammalian models-including primates, cats, and rodents-that inform our understanding of how neural activity in the SC underlies the selection of targets for movements. We then examine the anatomy and physiology of inputs to the SC from three key regions that are themselves implicated in motor decisions-the basal ganglia, parabrachial region, and neocortex-and discuss how they may influence SC activity related to target selection. Finally, we discuss the potential for methodological advances to further our understanding of the neural bases of target selection. Our overarching goal is to synthesize what is known about how the SC and its inputs act together to mediate the selection of targets for movements, to highlight open questions about this process, and to spur future studies addressing these questions.

In the treatment of brain tumors, surgical intervention remains a common and effective therapeutic option. Recent advances in neuroimaging have provided neurosurgeons with new tools to overcome the challenge of differentiating healthy tissue from tumor-infiltrated tissue, with the aim of increasing the likelihood of maximizing the extent of resection volume while minimizing injury to functionally important regions. Novel applications of diffusion tensor imaging (DTI), and DTI-derived tractography (DDT) have demonstrated that preoperative, non-invasive mapping of eloquent cortical regions and functionally relevant white matter tracts (WMT) is critical during surgical planning to reduce postoperative deficits, which can decrease quality of life and overall survival. In this review, we summarize the latest developments of applying DTI and tractography in the context of resective surgery and highlight its utility within each stage of the neurosurgical workflow: preoperative planning and intraoperative management to improve postoperative outcomes.

Decisions are influenced by recent experience, but the neural basis for this phenomenon is not well understood. Here, we address this question in the context of action selection. We focused on activity in the pedunculopontine tegmental nucleus (PPTg), a mesencephalic region that provides input to several nuclei in the action selection network, in well-trained mice selecting actions based on sensory cues and recent trial history. We found that, at the time of action selection, the activity of many PPTg neurons reflected the action on the previous trial and its outcome, and the strength of this activity predicted the upcoming choice. Further, inactivating the PPTg predictably decreased the influence of recent experience on action selection. These findings suggest that PPTg input to downstream motor regions, where it can be integrated with other relevant information, provides a simple mechanism for incorporating recent experience into the computations underlying action selection.DOI: http://dx.doi.org/10.7554/eLife.16572.001

Gliomas account for 26.5% of all primary central nervous system tumors. Recent studies have used diffusion tensor imaging (DTI) to extract white matter fibers and the diffusion coefficients derived from MR processing to provide useful, non-invasive insights into the extent of tumor invasion, axonal integrity, and gross differentiation of glioma from metastasis. Here, we extend this work by examining whether a tract-based analysis can improve non-invasive localization of tumor impact on white matter integrity. This study retrospectively analyzed preoperative magnetic resonance sequences highlighting contrast enhancement and DTI scans of 13 subjects that were biopsy-confirmed to have either high or low-grade glioma. We reconstructed the corticospinal tract and superior longitudinal fasciculus by applying atlas-based regions of interest to fibers derived from whole-brain deterministic streamline tractography. Within-subject comparison of hemispheric diffusion coefficients (e.g., fractional anisotropy and mean diffusivity) indicated higher levels of white matter degradation in the ipsilesional hemisphere. Novel application of along-tract analyses revealed that tracts traversing the tumor region showed significant white matter degradation compared to the contralesional hemisphere and ipsilesional tracts displaced by the tumor.

27Despite the conserved function of aggression across taxa in obtaining critical 28 resources such as food and mates, serotonin's (5-HT) modulatory role on29 aggressive behavior appears to be largely inhibitory for vertebrates but stimulatory 30 for invertebrates. However, critical gaps exist in our knowledge of invertebrates that 31 need to be addressed before definitively stating opposing roles for 5-HT and 32 aggression. Specifically, the role of 5-HT receptor subtypes are largely unknown, as 33 is the potential interactive role of 5-HT with other neurochemical systems known to 34 play a critical role in aggression. Similarly, the influence of these systems in driving 35 sex differences in aggressive behavior of invertebrates is not well understood. Here, 36 we investigated these questions by employing complementary approaches in a 37 novel invertebrate model of aggression, the stalk-eyed fly. A combination of altered 38 social conditions, pharmacological manipulation and 5-HT 2 receptor knockdown by 39 siRNA revealed an inhibitory role of this receptor subtype on aggression.40 Additionally, we provide evidence for 5-HT 2 's involvement in regulating neuropeptide 41 F activity, a suspected inhibitor of aggression. However, this function appears to be 42 stage-specific, altering only the initiation stage of aggressive conflicts. Alternatively, 43 pharmacologically increasing systemic concentrations of 5-HT significantly elevated 44 the expression of the neuropeptide tachykinin, which did not affect contest initiation 45 but instead promoted escalation via production of high intensity aggressive 46 behaviors. Notably, these effects were limited solely to males, with female 47 aggression and neuropeptide expression remaining unaltered by any manipulation 3 48 that affected 5-HT. Together, these results demonstrate a more nuanced role for 5-49 HT in modulating aggression in invertebrates, revealing an important interactive role 50 with neuropeptides that is more reminiscent of vertebrates. The sex-differences 51 described here also provide valuable insight into the evolutionary contexts of this 52 complex behavior. 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 4 71 1. Introduction 72 73Serotonin (5-HT) appears to promote aggression in invertebrates (1,2), in 74 contrast to the largely inhibitory effect seen in vertebrates (3, but see 4). Much of 75 the empirical support for this dichotomy comes from studies using arthropod 76 invertebrates, with increased expression of overt aggressive behavior and greater 77 willingness to engage in conflict seen in decapod crustaceans (5-8), crickets (9), 78 ants (10,11), and dipteran flies (12-15) following pharmacological or genetic 79 elevations of 5-HT at the systemic level. While these findings support the 80 presumption that 5-HT has opposing effects on invertebrate aggression from 81 vertebrates, there are critical gaps in knowledge that need to be considered before 82 accurately stating that 5-HT exclusively modulates invertebrate aggression in a 83 positive mann...

Accurate assessment of the probability of success in an aggressive confrontation with a conspecific is critical to the survival and fitness of the individuals. Various game theory models have examined these assessment strategies under the assumption that contests should favor the animal with the greater resource-holding potential (RHP), body size typically being the proxy. Mutual assessment asserts that an individual can assess their own RHP relative to their opponent, allowing the inferior animal the chance to flee before incurring unnecessary costs. The model of self-determined persistence, however, assumes that an individual will fight to a set personal threshold, independent of their opponent’s RHP. Both models have been repeatedly tested using size as a proxy for RHP, with neither receiving unambiguous support. Here we present both morphological and neurophysiological data from size-matched and mismatched stalk-eyed fly fights. We discovered differing fighting strategies between winners and losers. Winners readily escalated encounters to higher intensity and physical contact and engaged in less low-intensity, posturing behaviors compared with losers. Although these fighting strategies were largely independent of size, they were associated with elevated levels of 5-HT. Understanding the neurophysiological factors responsible for mediating the motivational state of opponents could help resolve the inconsistencies seen in current game theory models. Therefore, we contend that current studies using only size as a proxy for RHP may be inadequate in determining the intricacies of fighting ability and that future studies investigating assessment strategies and contest outcome should include neurophysiological data.

Experimental observations of very low frequency (VLF) triggered emissions are an important resource in investigation of nonlinear wave‐particle interactions between whistler mode waves and energetic electrons in the Earth's radiation belts. Magnetospherically generated whistler mode sidebands observed during the Siple Station wave injection experiment are analyzed using a mixed modulation model and the MINUIT minimization package. The observed sidebands are found to exhibit features of both amplitude and frequency modulation of the input carrier wave with frequency modulation becoming more prominent as the observed amplitudes of the carrier and sidebands increase. A nonlinear whistler mode wave growth formulation based on phase bunching of counterstreaming electrons within a well‐defined phase trap is shown to reproduce the salient features of the sideband observations. Whistler mode sideband amplitude is shown to be affected by the shape and uniformity of the trap.