From molecule to behavior: hypocretin/orexin revisited from a sex-dependent perspective

The hypocretin/orexin (Hcrt/Orx) system in the perifornical lateral hypothalamus has been recognized as a critical node in a complex network of neuronal systems controlling both physiology and behavior in vertebrates. Our understanding of the Hcrt/Orx system and its array of functions and actions have grown exponentially in merely two decades. This review will examine the latest progress in discerning the roles played by the Hcrt/Orx system in the regulation of homeostatic functions and in the execution of instinctive and learned behaviors. Furthermore, the gaps that currently exist in our knowledge of sex-related differences in this field of study are discussed.

The Role of the Learner in the Cultural Evolution of Vocalizations

As a uniquely human behavior, language is crucial to our understanding of ourselves and of the world around us. Despite centuries of research into how languages have historically developed and how people learn them, fully understanding the origin and evolution of language remains an ongoing challenge. In parallel, researchers have studied the divergence of birdsong in vocal-learning songbirds to uncover broader patterns of cultural evolution. One approach to studying cultural change over time, adapted from biology, focuses on the transmission of socially learned traits, including language, in a population. By studying how learning and the distribution of cultural traits interact at the population level, we can better understand the processes that underlie cultural evolution. Here, we take a two-fold approach to understanding the cultural evolution of vocalizations, with a focus on the role of the learner in cultural transmission. First, we explore previous research on the evolution of social learning, focusing on recent progress regarding the origin and ongoing cultural evolution of both language and birdsong. We then use a spatially explicit population model to investigate the coevolution of culture and learning preferences, with the assumption that selection acts directly on cultural phenotypes and indirectly on learning preferences. Our results suggest that the spatial distribution of learned behaviors can cause unexpected evolutionary patterns of learning. We find that, intuitively, selection for rare cultural phenotypes can indirectly favor a novelty-biased learning strategy. In contrast, selection for common cultural phenotypes leads to cultural homogeneity; we find that there is no selective pressure on learning strategy without cultural variation. Thus, counterintuitively, selection for common cultural traits does not consistently favor conformity bias, and novelty bias can stably persist in this cultural context. We propose that the evolutionary dynamics of learning preferences and cultural biases can depend on the existing variation of learned behaviors, and that this interaction could be important to understanding the origin and evolution of cultural systems such as language and birdsong. Selection acting on learned behaviors may indirectly impose counterintuitive selective pressures on learning strategies, and understanding the cultural landscape is crucial to understanding how patterns of learning might change over time.

Models of heterogeneous dopamine signaling in an insect learning and memory center

The Drosophila mushroom body exhibits dopamine dependent synaptic plasticity that underlies the acquisition of associative memories. Recordings of dopamine neurons in this system have identified signals related to external reinforcement such as reward and punishment. However, other factors including locomotion, novelty, reward expectation, and internal state have also recently been shown to modulate dopamine neurons. This heterogeneity is at odds with typical modeling approaches in which these neurons are assumed to encode a global, scalar error signal. How is dopamine dependent plasticity coordinated in the presence of such heterogeneity? We develop a modeling approach that infers a pattern of dopamine activity sufficient to solve defined behavioral tasks, given architectural constraints informed by knowledge of mushroom body circuitry. Model dopamine neurons exhibit diverse tuning to task parameters while nonetheless producing coherent learned behaviors. Notably, reward prediction error emerges as a mode of population activity distributed across these neurons. Our results provide a mechanistic framework that accounts for the heterogeneity of dopamine activity during learning and behavior.

Locus Coeruleus Norepinephrine in Learned Behavior: Anatomical Modularity and Spatiotemporal Integration in Targets

The locus coeruleus (LC), a small brainstem nucleus, is the primary source of the neuromodulator norepinephrine (NE) in the brain. The LC receives input from widespread brain regions, and projects throughout the forebrain, brainstem, cerebellum, and spinal cord. LC neurons release NE to control arousal, but also in the context of a variety of sensory-motor and behavioral functions. Despite its brain-wide effects, much about the role of LC-NE in behavior and the circuits controlling LC activity is unknown. New evidence suggests that the modular input-output organization of the LC could enable transient, task-specific modulation of distinct brain regions. Future work must further assess whether this spatial modularity coincides with functional differences in LC-NE subpopulations acting at specific times, and how such spatiotemporal specificity might influence learned behaviors. Here, we summarize the state of the field and present new ideas on the role of LC-NE in learned behaviors.

Heritable differences in synaptic zinc-transporter levels drive variation in learned birdsong

Complex learned behaviors exhibit striking variation within populations, yet how heritable factors contribute to such inter-individual differences remains largely unknown. Here, we used behavioral-genetic analysis within a Bengalese finch population (Lonchura striata domestica) to investigate molecular and circuit mechanisms underlying heritable differences in the tempo of learned birdsong. We identified a genomic locus encoding the zinc transporter ZIP11 and found that zip11(SLC39A11) transcript was expressed at higher levels in song control circuitry of faster singing birds. Reducing soluble zinc increased synaptic currents in motor circuitry and accelerated song, whereas reducing ZIP11 slowed song. Our results reveal a novel zinc-dependent mechanism that modulates neural activity to drive differences in behavior and suggest that natural variation in learning may preferentially target modulatory processes rather than core neural machinery.

Leveraging Lawyers’ Strengths and Training Them to Support Team Problem-Solving Under Crisis Conditions

Legal training and expertise equip crisis lawyers with powerful capabilities to help lead in a crisis; yet some of their learned behaviors and tendencies may create significant impediments to successful crisis resolution. In the context of the groundbreaking meta-leadership model developed jointly by scholars at the Harvard School of Public Health and Kennedy School of Government, this chapter discusses how lawyers can successfully cultivate and leverage their legal education, skills, experience, and problem-solving abilities to help lead in a crisis. It also offers suggestions as to how to train lawyers to improve their self-awareness of and help to mitigate against counterproductive activities and reactions that they may exhibit when under stress in a crisis.

Population turnover facilitates cultural selection for efficiency

Selection for more efficient socially learned behaviors over alternatives is crucial for cumulative cultural evolution, yet our understanding of such cultural selection in animals is limited. We performed a cultural diffusion experiment using 18 populations of wild-caught great tits Parus major to ask whether more efficient foraging traditions are selected for, and whether this process is affected by turnover. We show that gradual replacement of individuals greatly increases the probability that a more efficient behavior will invade a population's cultural repertoire, out-competing an established inefficient behavior. Turnover does not increase innovation rates, but instead increases adoption rates, as immigrants are more susceptible to novel, efficient behaviors. An agent based model further supported our results by demonstrating that this effect holds across populations of different types of learners. Altogether, these results provide strong evidence for cultural selection for efficiency in animals, and highlight the importance of population turnover for this process.

Population turnover facilitates cultural selection for efficiency

Selection for more efficient socially learned behaviors over alternatives is crucial for cumulative cultural evolution, yet our understanding of such cultural selection in animals is limited. We performed a cultural diffusion experiment using 18 populations of wild-caught great tits Parus major to ask whether more efficient foraging traditions are selected for, and whether this process is affected by turnover. We show that gradual replacement of individuals greatly increases the probability that a more efficient behavior will invade a population's cultural repertoire, out-competing an established inefficient behavior. Turnover does not increase innovation rates, but instead increases adoption rates, as immigrants are more susceptible to novel, efficient behaviors. An agent based model further supported our results by demonstrating that this effect holds across populations of different types of learners. Altogether, these results provide strong evidence for cultural selection for efficiency in animals, and highlight the importance of population turnover for this process.

Remembrance of things practiced with fast and slow learning in cortical and subcortical pathways

The learning of motor skills unfolds over multiple timescales, with rapid initial gains in performance followed by a longer period in which the behavior becomes more refined, habitual, and automatized. While recent lesion and inactivation experiments have provided hints about how various brain areas might contribute to such learning, their precise roles and the neural mechanisms underlying them are not well understood. In this work, we propose neural- and circuit-level mechanisms by which motor cortex, thalamus, and striatum support motor learning. In this model, the combination of fast cortical learning and slow subcortical learning gives rise to a covert learning process through which control of behavior is gradually transferred from cortical to subcortical circuits, while protecting learned behaviors that are practiced repeatedly against overwriting by future learning. Together, these results point to a new computational role for thalamus in motor learning and, more broadly, provide a framework for understanding the neural basis of habit formation and the automatization of behavior through practice.