Biology subjects

Chevee, M.

Publications and source records attributed to Chevee, M..

3 recordsLinked to original sources

bioRxiv2024

A consensus definition for deep layer 6 excitatory neurons in mouse neocortex

To understand neocortical function, we must first define its cell types. Recent studies indicate that neurons in the deepest cortical layer play roles in mediating thalamocortical interactions and modulating brain state and are implicated in neuropsychiatric disease. However, understanding the functions of deep layer 6 (L6b) neurons has been hampered by the lack of agreed upon definitions for these cell types. We compared commonly used methods for defining L6b neurons, including molecular, transcriptional and morphological approaches as well as transgenic mouse lines, and identified a core population of L6b neurons. This population does not innervate sensory thalamus, unlike layer 6 corticothalamic neurons (L6CThNs) in more superficial layer 6. Rather, single L6b neurons project ipsilaterally between cortical areas. Although L6b neurons undergo early developmental changes, we found that their intrinsic electrophysiological properties were stable after the first postnatal week. Our results provide a consensus definition for L6b neurons, enabling comparisons across studies.

neuroscience↗

bioRxiv2023

Sensitivity to outcome devaluation in operant tasks is better predicted by food restriction level than reinforcement training schedule in mice

Behavioral strategies are often classified based on whether reinforcement is controlled by the value of the reinforcer. Value-sensitive behaviors, in which animals update their actions when reinforcer value is changed, are classified as goal-directed; conversely, value-insensitive actions, where behavior remains consistent when the reinforcer is removed or devalued, are considered habitual. Understanding the features of operant training that bias behavioral control toward either strategy is essential to understanding the cognitive and neuronal processes on which they rely. Using basic reinforcement principles, behavior can be biased toward relying on either process: random ratio (RR) schedules are thought to promote the formation of goal-directed behaviors while random intervals (RI) promote habitual control. However, how the schedule-specific features of these task structures relate to external factors to influence behavior is not well understood. Using male and female mice on distinct food restriction levels, we trained each group on RR schedules with responses-per-reinforcer rates matched to their RI counterparts to control for differences in reinforcement rate. We determined that food restriction level has a stronger effect on the behavior of mice following RR schedules than mice following RI schedules and that food restriction better predicted sensitivity to outcome devaluation than training schedule. Our results support the idea the relationships between RR or RI schedules with goal-directed or habitual behaviors, respectively, are more nuanced than previously appreciated and suggest that an animals engagement in a task must be accounted for, together with the structure of reinforcement schedules, to appropriately interpret the cognitive underpinnings of behavior. Significance statementUnderstanding the basic learning principles that control behavior is essential to developing therapies for psychiatric disorders such as addiction or obsessive-compulsive disorder. Reinforcement schedules are thought to control the reliance on habitual versus goal-directed control during adaptive behaviors. However, external factors that are independent of training schedule also influence behavior, for example by modulating motivation or energy balance. In this study, we find that food restriction levels are at least equally important as reinforcement schedules in shaping adaptive behavior. Our results add to the growing body of work showing the distinction between habitual and goal-directed control is nuanced.

neuroscience↗

bioRxiv2022

Schedule-dependent production of stereotyped sequences of actions

Concatenating actions into automatic routines is evolutionarily advantageous as it allows organisms to efficiently use time and energy under predictable conditions. However, over reliance on inflexible behaviors can be life-threatening in a changing environment and can become pathological in disease states such as obsessive-compulsive disorder (OCD) and substance use disorder (SUD). Understanding the conditions under which stereotypical sequences of actions are produced is crucial to studying how these behaviors can become maladaptive. Here, we investigated the ability of operant conditioning schedules and contingencies to promote reproducible sequences of five lever presses. We found that signaling reinforcer delivery with a visual cue was effective at increasing learning rates but resulted in mice pressing the lever in fast succession until the cue turned on, rather than pressing it five times. We also found that requiring mice to collect their reinforcer between sequences had little effect on both rate of behavior and on quantitative metrics of reproducibility such as interresponse interval (IRI) variance, and that a training strategy that directly reinforced sequences with low variance IRIs was not more effective than a traditional fixed ratio schedule at promoting reproducible action execution. Together, our findings provide insights into the parameters of behavioral training that promote reproducible sequences and serve as a roadmap to investigating the neural substrates of automatic behaviors.

animal behavior and cognition↗