Biology subjects

Vigotsky, A. D.

Publications and source records attributed to Vigotsky, A. D..

5 recordsLinked to original sources

bioRxiv2022

Pattern of Self-Administered Vapor Fentanyl Exposure Determines Long-term Behavior Consequences, in Mice with or without Neuropathic Pain

We studied the behavioral consequences of fentanyl vapor self-administration (SA) in mice with and without chronic neuropathic pain (one month after spared-nerve injury(SNI) model or sham injury). We assessed fentanyl consumption, motivation, and seeking during as well as anxiety, hyperactivity, immobility, and pain for two regimens of fentanyl SA: 1) Dose escalation, where over a 3-week period mice are exposed (daily 2-hour sessions) to escalating numbers of fentanyl puffs per active nosepoke (from 1 puff/active nosepoke for first 3 days, up to 6 puffs/active nosepoke in days 16-18). 2) Effort escalation, where over a 3-week period (daily 2-hour sessions) mice need to increase effort to acquire the same amount of fentanyl (fixed ratio 1 (FR) = 1 active nosepoke results in 1 fentanyl puff, while second and third week we use FR5 and FR10). We observe sex-, injury- and regimen-dependent differences in outcomes. Importantly the dose escalation regimen resulted in higher seeking behavior (post forced abstinence, context and cue driven nosepoking in the absence of fentanyl delivery), long lasting increased anxiety, immobility, and hyperactivity, as well as transient but full pain relief in SNI mice. Therefore, this regimen seems a better rodent model for translating outcomes to human chronic pain patients managed with opioids.

neuroscience↗

bioRxiv2022

Widespread, perception-related information in the human brain scales with levels of consciousness

How does the human brain generate coherent, subjective perceptions--transforming yellow and oblong visual sensory information into the perception of an edible banana 1? This is a hard problem. The standard viewpoint posits that anatomical and functional networks integrate local, specialized processing across the brain to somehow construct unique percepts. Here, we provide evidence for a novel organizational concept by uncovering task-specific information distributed across the human brain. First, we show that functional magnetic resonance imaging (fMRI) can uncover task-specific information throughout the neocortex, even across voxels traditionally discarded as "noise" (t-statistics {approx} 0), challenging the sensitivity of traditional linear, univariate analytical approaches. Remarkably, task-specific signals could also be uncovered from across-subject variances and were ubiquitous even in the subcortex and cerebellum. Finally, we show that the widespread signal in regions remote from a tasks primary and secondary sensory cortices depends on the level of sedation, suggesting it is related to perception{dagger} rather than sensory stimulus encoding. We hypothesize that these widespread, task-specific, and consciousness level-dependent signals may be the basis for coherent, subjective perceptions.

neuroscience↗

bioRxiv2022

Effects of variability in manually contoured spinal cord masks on fMRI co-registration and interpretation

Functional magnetic resonance imaging (fMRI) of the human spinal cord (SC) is a unique non-invasive method for characterizing neurovascular responses to stimuli. Group-analysis of SC fMRI data involves co-registration of subject-level data to standard space, which requires manual masking of the cord and may result in bias of group-level SC fMRI results. To test this, we examined variability in SC masks drawn in fMRI data from 21 healthy participants from a completed study mapping responses to sensory stimuli of the C7 dermatome. Masks were drawn on temporal mean functional image by eight raters with varying levels of neuroimaging experience, and the rater from the original study acted as a reference. Spatial agreement between rater and reference masks was measured using the Dice Similarity Coefficient, and the influence of rater and dataset was examined using ANOVA. Each raters masks were used to register functional data to the PAM50 template. Gray matter-white matter signal contrast of registered functional data was used to evaluate the spatial normalization accuracy across raters. Subject- and group-level analyses of activation during left- and right-sided sensory stimuli were performed for each raters co-registered data. Agreement with the reference SC mask was associated with both rater (F(7,140) = 32.12, P < 2x10-16,{eta} 2 = 0.29) and dataset (F(20,140) = 20.58, P < 2x10-16,{eta} 2 = 0.53). Dataset variations may reflect image quality metrics: the ratio between the signal intensity of spinal cord voxels and surrounding cerebrospinal fluid was correlated with DSC results (p<0.001). As predicted, variability in the manually-drawn masks influenced spatial normalization, and GM:WM contrast in the registered data showed significant effects of rater and dataset (rater: F(8,160) = 23.57, P < 2x10-16,{eta} 2 = 0.24; dataset: F(20,160) = 22.00, P < 2x10-16,{eta} 2 = 0.56). Registration differences propagated into subject-level activation maps which showed rater-dependent agreement with the reference. Although group-level activation maps differed between raters, no systematic bias was identified. Increasing consistency in manual contouring of spinal cord fMRI data improved co-registration and inter-rater agreement in activation mapping, however our results suggest that improvements in image acquisition and post-processing are also critical to address.

neuroscience↗

bioRxiv2021

Motor unit recruitment patterns of the quadriceps differ between continuous high- and low-torque isometric knee extension to momentary failure

The size principle is a theory of motor unit (MU) recruitment that suggests MUs are recruited in an orderly manner from the smallest (lower threshold) to the largest (higher threshold) MUs. A consequence of this biophysical theory is that, for isometric contractions, recruitment is dependent on the intensity of actual effort required to meet task demands. This concept has been supported by modelling work demonstrating that, in tasks performed to momentary failure, full MU recruitment will have occurred upon reaching failure irrespective of the force requirements of the task. However, in vivo studies examining this are limited. Therefore, the aim of the current study was to examine MU recruitment of the quadriceps under both higher- and lower-torque (70% and 30% of MVC, respectively) isometric knee extension, performed to momentary failure. Specifically, we compared surface electromyography (sEMG) frequency characteristics, determined by wavelet analysis, across the two continuous isometric knee extension tasks to identify potential differences in recruitment patterns. A convenience sample of 10 recreationally active adult males (height: 179.6{+/-}6.0 cm; mass: 76.8{+/-}7.3 kg; age: 26{+/-}7 years) with previous resistance training experience (6{+/-}3 years) were recruited. Using a within-session, repeated-measures, randomised crossover design participants performed the knee extension tasks whilst sEMG was collected from the vastus medialis (VM), rectus femoris (RF) and vastus lateralis (VL). Myoelectric signals were decomposed into intensities as a function of time and frequency using an EMG-specific wavelet transformation. Our first analysis compared the mean frequency at momentary failure; second, we investigated the effects of load on relative changes in wavelet intensities; finally, we quantified the degree of wavelet similarity over time. Wavelet-based calculation of the mean signal frequency appeared to show similar mean frequency characteristics occurring when reaching momentary failure. However, individual wavelets revealed that different changes in frequency components occurred between the two tasks, suggesting that patterns of recruitment differed. Low-torque conditions resulted in an increase in intensity of all frequency components across the trials for each muscle whereas high-torque conditions resulted in a wider range of frequency components contained within the myoelectric signals at the beginning of the trials. However, as the low-torque trial neared momentary failure there was an increased agreement between conditions across wavelets. Our results corroborate modelling studies as well as recent biopsy evidence, suggesting overall MU recruitment may largely be similar for isometric tasks performed to momentary failure with the highest threshold MUs likely recruited, despite being achieved with differences in the pattern of recruitment over time utilised.

physiology↗

bioRxiv2020

The Hard Limits of Decoding Mental States: The Decodability of fMRI

High-profile studies claim to assess mental states across individuals using multi-voxel decoders of brain activity. The fixed, fine-grained, multi-voxel patterns in these "optimized" decoders are purportedly necessary for discriminating between, and accurately identifying, mental states. Here, we present compelling evidence that the efficacy of these decoders is overstated. Across a variety of tasks, decoder patterns were not necessary. Not only were "optimized decoders" spatially imprecise and 90% redundant, but they also performed similarly to simpler decoders, built from average brain activity. We distinguish decoder performance when used for discriminating between, in contrast to identifying, mental states, and show even when discrimination performance is strong, identification can be poor. Using similarity rules, we derived novel and intuitive discriminability metrics that capture 95% and 68% of discrimination performance within- and across-subjects, respectively. These findings demonstrate that current across-subject decoders remain inadequate for real-life decision making.

neuroscience↗