Biology subjects

Palmer, J. A.

Publications and source records attributed to Palmer, J. A..

10 recordsLinked to original sources

bioRxiv2025

Active Sampling and Sex Differences in Perceptual Decision Making in Rats

Decisions are often modeled as a sequential process in which evidence accumulates until it reaches a threshold, triggering a response. Studies in freely moving animals raise questions about how ongoing behavior, not just stimulus properties, shapes this process. We trained rats of both sexes on a visual detection task with three luminance levels, each associated with the same reward outcome. Rats controlled cue duration through sustained head entries into a center port, yielding a measurable index of active sampling. Females consistently sampled longer than males. Sampling durations were shorter on error than correct trials, and reaction times were longer on error trials. We used drift diffusion models to relate these behaviors to the decision process. Luminance selectively affected the rate of evidence accumulation, with drift rate increasing monotonically across low, mid, and high luminance levels. Active sampling time was associated with the decision threshold, with longer sampling predicting higher thresholds in both sexes. The relationship between sampling time and drift rate differed by sex. Females showed a negative association between sampling duration and drift rate that was absent in males. These findings suggest that cue properties and active sampling make separable contributions to the decision process. These findings suggest that cue properties and active sampling make separable contributions to decision making, with a negative association between sampling duration and drift rate evident in females but not males.

neuroscience↗

bioRxiv2025

Visual Salience Controls the Speed of Evidence Accumulation in Value-Based Decisions by Rats

Studies of visual discrimination in rodents can confound the effects of cue salience with reward value, making it difficult to determine which factor guides choice behavior. We examined this issue by testing how changes in relative salience affect decision dynamics in rats performing a two-alternative forced-choice task in which rats chose between visual cues associated with high or low sucrose rewards. After initial training with high and low luminance cues, we introduced a novel cue of intermediate luminance as a "luminance shift" test. The intermediate luminance cue substituted for either the brighter or dimmer cue and had the same reward value as the cue that it replaced. We found that while rats maintained a preference for the higher-value option, the introduction of a perceptually more similar cue consistently reduced choice preference and eliminated latency differences compared to baseline. Using drift diffusion modeling, we determined that the luminance shifts primarily caused a reduction in the drift rate (the speed of evidence accumulation), reflecting increased difficulty in cue discrimination. This finding suggests that the relative salience of the options determines the efficiency of evidence accumulation in value-based decisions. Furthermore, this effect on drift rate shows a dissociation from our previous work (Palmer et al., 2024), where prefrontal cortex inactivation specifically affected only the decision threshold. Our results demonstrate that relative salience influences deliberation, with low-level perceptual features shaping the computational dynamics of value-based choice. Our findings clarify the distinct contributions of sensory input and prefrontal function in the decision process. Significance StatementThis study reveals that changes in the relative salience of visual stimuli shape the computational dynamics of value-based decisions. We trained rats to make visually guided choices and found that relative differences in the brightness of the stimuli affect how quickly the rats made decisions and how often they chose a higher-value option. Our findings, together with a recent study on the role of the prefrontal cortex in value-guided decisions (Palmer et al., 2024), suggest that separate factors influence choice dynamics in rodents: visual salience affects the speed of deliberation, while prefrontal activity regulates caution. This study helps clarify how sensory and higher cognitive variables relate to the distinct computational components of the decision process.

neuroscience↗

bioRxiv2025

APOE4 carriers resistant to cognitive decline show unique relationships between cerebrovascular response to exercise and dual-task cognitive-balance performance

BACKGROUNDEmerging research indicates cognitive dual-tasking is an early marker for cognitive impairment, with particular implications for Apolipoprotein E4 (APOE4) carriers who are at higher genetic risk for Alzheimers disease. While APOE4 carriers typically show accelerated cognitive decline and impaired cerebrovascular function with aging, exceptions to this norm exist and may provide insights into resilience mechanisms. The relationship between cerebrovascular response and cognitive-motor dual-task performance in cognitively-normal APOE4 carriers who maintain preserved function remains unclear. METHODSThirty cognitively-normal older adults (76{+/-}4 years, 8 APOE4 carriers, 22 noncarriers) completed clinical balance and cognitive testing under single-task and dual-task conditions. Balance performance was assessed as distance traversed during challenging beam walking. Cognitive performance was assessed as response time during an auditory Stroop test. Transcranial Doppler ultrasound measured cerebrovascular response to moderate-intensity aerobic exercise. We tested group differences in cognitive-balance dual task performance and relationships between cerebrovascular response and dual-task interference (DTI) in balance and cognitive domains, and effects of APOE4 genotype on these relationships. RESULTSNo differences in cerebrovascular response or dual-task performance were observed between APOE4 carriers and noncarriers. However, APOE4 carriers displayed unique cerebrovascular-behavioral relationships. In APOE4 carriers, higher cerebrovascular response to exercise was associated with less balance DTI (r=0.839, p=0.009) and less cognitive DTI (r=0.832, p=0.020), while no relationships were observed in noncarriers (p>0.187). CONCLUSIONSCognitively-normal APOE4 carriers with preserved cognitive-balance dual-task function represent exceptions that may model aging resilience mechanisms. The unique cerebrovascular-behavioral relationships suggest that maintaining cerebrovascular function provides preliminary support for neuromotor and neurocognitive resilience to dual-task challenges in genetically vulnerable populations.

physiology↗

bioRxiv2024

The role of rat prelimbic cortex in decision making

The frontal cortex plays a critical role in decision-making. One specific frontal area, the anterior cingulate cortex, has been identified as crucial for setting a threshold for how much evidence is needed before a choice is made (Domenech & Dreher, 2010). Threshold is a key concept in drift diffusion models, a popular framework used to understand decision-making processes. Here, we investigated the role of the prelimbic cortex, part of the rodent cingulate cortex, in decision making. Male and female rats learned to choose between stimuli associated with high and low value rewards. Females learned faster, were more selective in their responses, and integrated information about the stimuli more quickly. By contrast, males learned more slowly and showed a decrease in their decision thresholds during choice learning. Inactivating the prelimbic cortex in female and male rats sped up decision making without affecting choice accuracy. Drift diffusion modeling found selective effects of prelimbic cortex inactivation on the decision threshold, which was reduced with increasing doses of the GABA-A agonist muscimol. Stimulating the prelimbic cortex through mu opioid receptors slowed the animals choice latencies and increased the decision threshold. These findings provide the first causal evidence that the prelimbic cortex directly influences decision processes. Additionally, they suggest possible sex-based differences in early choice learning.

neuroscience↗

bioRxiv2024

Habit learning shapes activity dynamics in the central nucleus of the amygdala

As animals perform instrumental tasks, they may develop a habit response with extended experience. Habits are automatic, inflexible, outcome value insensitive behaviors that are regulated by a network of brain regions including the central nucleus of the amygdala (CeA). Prior work has demonstrated that the CeA governs motivational pursuit and is necessary for habit formation. However, the behavioral features that CeA neurons encode in habit formation remain relatively unknown. To address this, we first used male and female Long-Evans rats to quantify CeA cFos expression after performance of a maze task. There, we found that animals with extended training show elevated cFos expression. Then, we implanted animals with drivable silicon probes to record in-vivo single unit electrophysiological activity from the CeA as animals developed habit responding on the maze. We observed significant activity during outcome consumption late in training while also observing elevated unit activity when animals consumed outcomes of larger magnitudes. Outcome related activity did not persist during probe tests following outcome devaluation, despite animals continuing to perform the task. Together, these data add to growing evidence that suggests that the CeA is involved in motivational processes that contribute to the development of habit formation.

neuroscience↗

bioRxiv2023

Cerebrovascular-balance relationships reveal mechanisms of neuromotor resilience to dual-task cognitive loading

BACKGROUNDAge-related decline in cerebrovascular health precipitates cognitive dysfunction and can be attenuated by habitual physical activity. Cognitive interference in balance control is well-known clinically and reflects compromised neuromotor resilience. However, whether cerebrovascular health affects cognitive-balance dual-tasking with aging is unclear. METHODSThirty participants (76{+/-}4years) completed clinical balance/cognitive testing under single-task and dual-task conditions. Balance performance was assessed as the total distance traversed during a challenging beam walking task. Cognitive performance was assessed as response time (RT) during a working-memory n-back test. Transcranial Doppler ultrasound was used to measure resting middle cerebral artery blood velocity (MCAv). We tested whether MCAv was associated with single-task and dual-task interference (DTI) in balance and cognitive performance and the effects of age and physical activity level on this relationship. RESULTSDuring single-tasking, higher MCAv associated with higher balance function (r=0.40, p=0.033), while no relationship was observed for cognitive performance. Dual-tasking strengthened relationships between MCAv and DTI across domains of balance (r=0.442, p=0.016) and cognition (r=0.328, p=0.089); for cognitive DTI, this effect was driven by individuals [≥]75years old (r=0.54, p=0.031). Individuals [≥]75years exhibited greater cognitive DTI (p=0.049), yet achieved similar balance DTI compared to those <75. Regardless of age, participants with higher MCAv demonstrated greater dual-task prioritization of balance control over cognitive performance (r=0.410, p=0.030). Physically-active participants with higher MCAv also showed less balance DTI (r=0.621, p=0.003), while there was no relationship in under-active/sedentary individuals or within the cognitive domain. CONCLUSIONSOur results support a key role of cerebrovascular health in neuromotor resilience to cognitive loading, which may emerge earlier in brain aging processes affecting balance control compared to cognition. Cerebrovascular health may support peoples ability to prioritize balance in the face of competing attentional demands, and may mediate the positive effects of physical activity on cortically-mediated balance control.

neuroscience↗

bioRxiv2023

Task history dictates how the dorsolateral striatum controls action strategy and vigor

The dorsolateral striatum (DLS) is linked to the learning and honing of action routines. However, the DLS is also important for performing behaviors that have been successful in the past. The learning function can be thought of as prospective, helping to plan ongoing actions to be efficient and often optimal. The performance function is more retrospective, helping the animal continue to behave in a way that had worked previously. How the DLS manages this all is curious. What happens when a learned behavior becomes sub-optimal due to environment changes. In this case, the prospective function of the DLS would cause animals to (adaptively) learn and plan more optimal actions. In contrast, the retrospective function would cause animals to (maladaptively) favor the old behavior. Here we find that, during a change in learned task rules, DLS inhibition causes animals to adjust less rapidly to the new task (and to behave less vigorously) in a maladaptive way. Yet, when the task is changed back to the initially learned rules, DLS inhibition instead causes a rapid and vigorous adjustment of behavior in an adaptive way. These results show that inhibiting the DLS biases behavior towards initially acquired strategies, implying a more retrospective outlook in action selection when the DLS is offline. Thus, an active DLS could encourage planning and learning action routines more prospectively. Moreover, the DLS control over behavior can appear to be either advantageous/flexible or disadvantageous/inflexible depending on task context, and its control over vigor can change depending on task context. Significant StatementBasal ganglia networks aid behavioral learning (a prospective planning function) but also favor the use of old behaviors (a retrospective performance function), making it unclear what happens when learned behaviors become suboptimal. Here we inhibit the dorsolateral striatum (DLS) as animals encounter a change in task rules, and again when they shift back to those learned task rules. DLS inhibition reduces adjustment to new task rules (and reduces behavioral vigor), but it increases adjustment back to the initially learned task rules later (and increases vigor). Thus, in both cases, DLS inhibition favored the use of the initially learned behavioral strategy, which could appear either maladaptive or adaptive. We suggest that the DLS might promote a prospective orientation of action control.

animal behavior and cognition↗

bioRxiv2022

Hippocampal blood flow rapidly and preferentially increases after a bout of moderate-intensity exercise in older adults with poor cerebrovascular health

Over the course of aging, there is an early degradation of cerebrovascular health that may be attenuated with aerobic exercise training. Yet, the acute cerebrovascular response to a single bout of exercise remains elusive, particularly within key brain regions most affected by age-related disease processes. We investigated the acute global and region-specific cerebral blood flow (CBF) response to 15 minutes of moderate-intensity aerobic exercise in older adults ([≥]65years) (n=60) using arterial spin labeling magnetic resonance imaging. Within 0-6 minutes post-exercise, CBF decreased across all regions, an effect that was attenuated in the hippocampus. The exercise-induced CBF drop was followed by a rebound effect over the 24-minute post-exercise assessment period, an effect that was most robust in the hippocampus. Individuals with low baseline perfusion demonstrated the greatest hippocampal-specific CBF effect post-exercise, showing no immediate drop and a rapid increase in CBF that exceeded baseline levels within 6-12 minutes post-exercise. Gains in domain-specific cognitive performance post-exercise were not associated with changes in regional CBF, suggesting dissociable effects of exercise on acute neural and vascular plasticity. Together, the present findings support a precision-medicine framework for the use of exercise to target brain health that carefully considers age-related changes in the cerebrovascular system.

systems biology↗

bioRxiv2021

Lower cognitive set shifting ability is associated with stiffer balance recovery behavior and larger perturbation-evoked cortical responses in older adults

1.The mechanisms underlying associations between cognitive set shifting impairments and balance dysfunction are unclear. Cognitive set shifting refers to the ability to flexibly adjust behavior to changes in task rules or contexts, which could be involved in flexibly adjusting balance recovery behavior to different contexts, such as the direction the body is falling. Prior studies found associations between cognitive set shifting impairments and severe balance dysfunction in populations experiencing frequent falls. The objective of this study was to test whether cognitive set shifting ability is expressed in successful balance recovery behavior in older adults with high clinical balance ability (N=19, 71 {+/-} 7 years, 6 female). We measured cognitive set shifting ability using the Trail Making Test and clinical balance ability using the miniBESTest. For most participants, cognitive set shifting performance (Trail Making Test B-A = 37 {+/-} 20s) was faster than normative averages (46s for comparable age and education levels), and balance ability scores (miniBESTest = 25 {+/-} 2 / 28) were above the threshold for fall risk (23 for people between 70-80 years). Reactive balance recovery in response to support-surface translations in anterior and posterior directions was assessed in terms of body motion, muscle activity, and brain activity. Across participants, lower cognitive set shifting ability was associated with smaller peak center of mass displacement during balance recovery, lower directional specificity of late phase balance-correcting muscle activity (i.e., greater antagonist muscle activity 200-300ms after perturbation onset), and larger cortical N1 responses (100-200ms). None of these measures were associated with clinical balance ability. Our results suggest that cognitive set shifting ability is expressed in balance recovery behavior even in the absence of profound clinical balance disability. Specifically, our results suggest that lower flexibility in cognitive task performance is associated with lower ability to incorporate the directional context into the cortically-mediated later phase of the motor response. The resulting antagonist activity and stiffer balance behavior may help explain associations between cognitive set shifting impairments and frequent falls.

neuroscience↗

bioRxiv2020

Cortical beta oscillatory activity evoked during reactive balance recovery scales with perturbation difficulty and individual balance ability

I.Cortical beta oscillations (13-30 Hz) reflect sensorimotor cortical activity, but have not been fully investigated in balance recovery behavior. We hypothesized that more challenging balance conditions would lead to greater recruitment of cortical sensorimotor brain regions for balance recovery. We predicted that beta power would be enhanced when balance recovery is more challenging, either due to more difficult perturbations or due to lower intrinsic balance ability. In 19 young adults, we measured beta power evoked over motor cortical areas (Cz electrode) during 3 magnitudes of backward support-surface translational perturbations using electroencephalography. Peak beta power was measured during early (50-150 ms), late (150-250 ms), and overall (0-400 ms) time bins, and wavelet-based analyses quantified the time course of evoked beta power and agonist and antagonist ankle muscle activity. We further assessed the relationship between individual balance ability measured in a challenging beam walking task and perturbation-evoked beta power within each time bin. In balance perturbations, cortical beta power increased [~]50 ms after perturbation onset, demonstrating greater increases with increasing perturbation magnitude. Balance ability was negatively associated with peak beta power in only the late (150-250 ms) time bin, with higher beta power in individuals who performed worse in the beam walking task. Additionally, the time course of cortical beta power followed a similar waveform as the evoked muscle activity, suggesting these evoked responses may be initially evoked by shared underlying mechanisms. These findings support the active role of sensorimotor cortex in balance recovery behavior, with greater recruitment of cortical resources under more challenging balance conditions. Cortical beta power may therefore provide a biomarker for engagement of sensorimotor cortical resources during reactive balance recovery and reflect the individual level of balance challenge.

neuroscience↗