Biology subjects

Palmer, H.

Publications and source records attributed to Palmer, H..

8 recordsLinked to original sources

bioRxiv2020

Skill acquisition and gaze behavior during laparoscopic surgical simulation

BackgroundExperts consistently exhibit more efficient gaze behaviors than non-experts during motor tasks. In surgery, experts have been shown to gaze more at surgical targets than surgical tools during simple simulations and when watching surgical recordings, suggesting a proactive control strategy with greater use of feedforward visual sampling. To investigate such expert gaze behaviors in a more dynamic and complex laparoscopic surgery simulation, the current study measured and compared gaze patterns between surgeons and novices who practiced extensively with laparoscopic simulation. MethodsThree surgeons were assessed in a testing visit and five novices were trained and assessed (at pre-, mid-, and post-training points) in a 5-visit protocol on the Fundamentals of Laparoscopic Surgery peg transfer task. The task was adjusted to have a fixed action sequence to allow recordings of dwell durations based on pre-defined areas of interest (AOIs). Novices individualized learning curves were analyzed using an inverse function model, and group-level differences were tested using analysis of variance on both behavioral performance and dwell duration measures. ResultsTrained novices were shown to reach more than 98% (M = 98.62%, SD = 1.06%) of their behavioral learning plateaus, leading to equivalent behavioral performance to that of surgeons. Despite this equivalence in behavioral performance, surgeons continued to show significantly shorter dwell durations at visual targets of current actions and longer dwell durations at future steps in the action sequence than trained novices (ps [≤] .03, Cohens ds > 2). ConclusionThis study demonstrates that, whereas novices can train to match surgeons on behavioral performance, their gaze pattern is still less efficient than that of surgeons, suggesting that eye-tracking metrics might be more sensitive than behavioral performance in detecting surgical expertise. Such insight can be applied to develop training protocols so non-experts can internalize experts "gaze templates" to accelerate learning. Article SummaryGaze pattern differences persist between laparoscopic surgery experts and novices who have been trained to reach over 98% of individualized behavioral learning plateaus in the Fundamentals of Laparoscopic Surgery (FLS) peg transfer task. The importance of this finding lies in motivating the decision and method of including gaze behaviors via eyetracking technology in the present surgical training programs.

neuroscience↗

bioRxiv2020

Dose-dependent enhancement of motion direction discrimination with transcranial magnetic stimulation of visual cortex

Despite the widespread use of transcranial magnetic stimulation (TMS) in research and clinical care, the underlying mechanisms-of-actions that mediate modulatory effects remain poorly understood. To fill this gap, we studied dose-response functions of TMS for modulation of visual processing. Our approach combined electroencephalography (EEG) with application of single pulse TMS to visual cortex as participants performed a motion perception task. During participants first visit, motion coherence thresholds, 64-channel visual evoked potentials (VEPs), and TMS resting motor thresholds (RMT) were measured. In second and third visits, single pulse TMS was delivered 30 ms before the onset of motion or at the onset latency of the N2 VEP component derived from the first session. TMS was delivered at 0%, 80%, 100%, or 120% of RMT over the site of N2 peak activity, or at 120% over vertex. Behavioral results demonstrated a significant main effect of TMS timing on accuracy, with better performance when TMS was applied at N2-Onset timing versus Pre-Onset, as well as a significant interaction, indicating that 80% intensity produced higher accuracy than other conditions. TMS effects on VEPs showed reduced amplitudes in the 80% Pre-Onset condition, an increase for the 120% N2-Onset condition, and monotonic amplitude scaling with stimulation intensity. The N2 component was not affected by TMS. These findings reveal dose-response relationships between intensity and timing of TMS on visual perception and electrophysiological brain activity, generally indicating greater facilitation at stimulation intensities below RMT.

neuroscience↗

bioRxiv2019

Structural controllability predicts functional patterns and neuromodulatory benefits associated with working memory

The brain is an inherently dynamic system, and much work has focused on the ability to modify neural activity through both local perturbations and changes in the function of global network ensembles. Network controllability is a recent concept in network science that purports to predict the influence of individual cortical sites on global network states and state changes, thereby creating a unifying account of local influences on global brain dynamics. Here, we present an integrated set of multimodal brain-behavior relationships, acquired from functional magnetic resonance imaging during a transcranial magnetic stimulation intervention, that demonstrate how network controllability influences network function, as well as behavior. This work helps to outline a clear technique for integrating structural network topology and functional activity to predict the influence of a potential stimulation target on subsequent behaviors and prescribes next steps towards predicting neuromodulatory and behavioral responses after brain stimulation.\n\nHighlights- This study tested the strength of network controllability using fMRI and rTMS\n- Controllability correlates with functional modulation of working memory demand load\n- Controllability is also correlated with the memory improvement from applied rTMS\n- These findings link network control theory with physiology and behavior.\n\n\nIn briefBeynel et al. show that the benefits of functionally targeted brain stimulation on working memory performance can be predicted by network control properties at the stimulated site. Structural controllability and functional activity independently predict this cognitive benefit.\n\nAuthor ContributionsConceptualization & Methodology: L.B, S.W.D., B.L., R.C., L.G.A.; Investigation: L.B., L.D., S.W.D., C.A.C., M.D., H.P., S.H.; Writing--Original Draft: L.B., L.D., S.W.D.; Writing--Review & Editing: L.B., L.D., S.W.D., L.G.A., A.V.P.; Funding Acquisition: S.W.D., R.C., B.L., S.H.L., A.V.P.; Resources: L.G.A., B.L., R.C.; Supervision: L.G.A., S.W.D.

neuroscience↗

bioRxiv2019

Application of long-interval paired-pulse transcranial magnetic stimulation to motion-sensitive visual cortex does not lead to changes in motion perception

The perception of visual motion is dependent on a set of occipitotemporal regions which are readily accessible to neuromodulation. Previous studies using paired-pulse Transcranial Magnetic Stimulation (ppTMS) have provided evidence of the capacity of this type of protocols to modulate cognitive processes. To test whether such cortical modulation can be observed in the visual system, particularly during motion perception, ppTMS was applied to the occipital cortex using both scalp-based and meta-analytic targeting coordinates. In this within-subject, sham-controlled study, fifteen subjects completed two sessions in two consecutive weeks. On the first visit, subject-specific resting motor threshold (RMT) was determined and participants performed an adaptive motion discrimination task to determine individual motion sensitivity. During the second visit, subjects performed the same task with three individualized difficulty levels as two TMS pulses were delivered respectively -150 and -50 ms prior to motion stimulus onset at 120% RMT, under the logic that the cumulative inhibitory effect of these two pulses would alter motion sensitivity as measured by the individually calibrated task. The ppTMS was delivered at one of two locations: 3 cm dorsal and 5 cm lateral to inion (scalp-based coordinate), or at the site of peak activation for \"motion\" according to the NeuroSynth fMRI database (meta-analytic coordinate). Sham stimulation was delivered on one-third of trials and evenly between the two targets. Analyses showed no significant active-versus-sham effects of ppTMS when stimulation was delivered to the meta-analytic (p = 0.15) or scalp-based coordinates (p = 0.17), which were separated by 29 mm on average. Additionally, there was no was significant interaction between ppTMS at either location and task difficulty level (p = 0.12 and p = 0.33, respectively). These findings fail to support the hypothesis that long-interval ppTMS recruits inhibitory processes in motion-sensitive cortex, but must be considered within the limits of the current design choices.\n\nHIGHLIGHTSO_LILong-interval paired-pulse TMS was applied to visual cortex during a motion task\nC_LIO_LIThe ppTMS was delivered according to scalp and meta-analytic coordinates, as well as sham\nC_LIO_LINo effects of active-versus-sham stimulation were observed on motion task performance\nC_LI

neuroscience↗

bioRxiv2019

Older adults benefit from more widespread brain network integration during working memory

Neuroimaging evidence suggests that the aging brain relies on a more distributed set of cortical regions than younger adults in order to maintain successful levels of performance during demanding cognitive tasks. However, it remains unclear how task demands give rise to this age-related expansion in cortical networks. To investigate this issue, we used functional magnetic resonance imaging to measure univariate activity, network connectivity, and cognitive performance in younger and older adults during a working memory (WM) task. In the WM task investigated, participants hold letters online (maintenance) while reordering them alphabetically (manipulation). WM load was titrated to obtain four individualized difficulty levels. Network integration--defined as the ratio of within-versus between-network connectivity--was linked to individual differences in WM capacity. The study yielded three main findings. First, as task difficulty increased, network integration decreased in younger adults, whereas it increased in older adults. Second, age-related increases in network integration were driven by increases in right hemispheric connectivity to both left and right cortical regions, a finding that helps to reconcile extant theories of compensatory recruitment in aging to address the multivariate dynamics of global network functioning. Lastly, older adults with higher WM capacity demonstrated higher levels of network integration in the most difficult condition. These results shed light on the mechanisms of age-related network reorganization by suggesting that changes in network connectivity may act as an adaptive form of compensation, with older adults recruiting a more distributed cortical network as task demands increase.\n\nSignificance statementOlder adults often activate brain regions not engaged by younger adults, but the circumstances under which this widespread network emerges are unclear. Here, we examined the effects of aging on network connectivity between task regions recruited during a working memory (WM) manipulation task, and the rest of the brain. We found an age-related increase in the more global network integration in older adults, and an association between this integration and working memory capacity in older adults. The findings are generally consistent with the compensatory interpretation of these effects.

neuroscience↗

bioRxiv2019

Site-specific effects of online rTMS during a working memory task in healthy older adults.

The process of manipulating information within working memory (WM) is central to many cognitive functions, but also declines rapidly in old age. Given the importance of WM manipulation for maintaining healthy cognition, improving this process could markedly enhance health-span in older adults. The current pre-registered study tested the potential of online repetitive transcranial magnetic stimulation (rTMS) to enhance WM manipulation in healthy elderly adults. Online 5Hz rTMS was applied over the left lateral parietal cortex of 15 subjects to test the hypothesis that active rTMS would significantly improve performance compared to sham stimulation, and that these effects would be most pronounced in conditions with the highest cognitive demand. rTMS was applied while participants performed a delayed-response alphabetization task with two individually-titrated levels of difficulty. Sham stimulation was applied using an electrical sham coil that produced similar clicking sounds and somatosensory sensation as active stimulation but induced negligible effects on the brain. A stimulation site in left lateral parietal cortex was identified from fMRI activation maps and was targeted using individualized electric field modeling, stereotactic neuronavigation, and real-time robotic positioning, allowing optimal coil placement during the stimulation. Contrary to the a priori hypothesis, active rTMS significantly decreased accuracy relative to sham, and only in the hardest difficulty level. These results, therefore, demonstrate engagement of cortical WM processing, but not the anticipated facilitation, and provide a prescription for future studies that may attempt to enhance memory through application of different stimulation parameters.\n\nHighlightsO_LIThis study is one of the first attempts to enhance WM manipulation with online rTMS\nC_LIO_LIOnline 5Hz rTMS and sham were applied over the left parietal cortex of older adults\nC_LIO_LIIndividualized fMRI and electric field modeling were used to optimize targeting\nC_LIO_LIContrary to expectations, rTMS disrupted working memory manipulation abilities\nC_LIO_LIThis demonstrates that parietal cortex is involved in WM and modifiable with rTMS\nC_LI

neuroscience↗

bioRxiv2018

Utilizing Transcranial Direct Current Stimulation to Enhance Laparoscopic Technical Skills Training: A Randomized Controlled Trial

This study aimed to test the efficacy of transcranial direct current stimulation (tDCS) during laparoscopic skill training to determine if it has the capacity to accelerate technical skill acquisition. tDCS is a non-invasive brain stimulation technique that delivers constant, low electrical current resulting in changes to cortical excitability and prior work suggests it may enhance motor learning. We evaluate for the first time the potential of tDCS, coupled with motor skill training, to accelerate the development of laparoscopic technical skills. In this pre-registered, double-blinded and sham-controlled study, 60 healthy subjects were randomized into sham or active tDCS in either bilateral primary motor cortex (bM1) or supplementary motor area (SMA) electrode configurations. All subjects practiced the Fundamental of Laparoscopic Surgery Peg Transfer Task during a pre-test, six 20-minute training sessions, and a post-test. The primary outcome was change in laparoscopic skill performance over time, quantified by improvement in performance according to a seconds-per-object calculated score accounting for errors. Sixty participants were randomized equally into the three training cohorts (active bM1, active SMA, sham). The active groups had significantly greater improvement in performance from pre-test to post-test compared to the sham groups (108 vs 76 seconds, p = 0.018). Both bM1 and SMA active cohorts had significantly greater improvement in learning (p < 0.01), achieving the same skill level in 4 sessions compared to the 6 sessions required of the sham cohort. The SMA cohort had more variability in performance compared to the bM1 and control cohorts. Laparoscopic skill training with active, bM1 or SMA, tDCS exhibited significantly greater learning relative to training with sham tDCS. The potential for tDCS to enhance the training of surgical skills merits further investigation to determine if these preliminary results may be replicated.

clinical trials↗

bioRxiv2018

Complementary topology of maintenance and manipulation brain networks in working memory

Working memory (WM) is assumed to consist of a process that sustains memory representations in an active state (maintenance) and a process that operates on these activated representations (manipulation). Prior fMRI studies have examined maintenance and manipulation in separate task conditions, whereas in real life these processes operate simultaneously. In the current study, the neural mechanisms of maintenance and manipulation were disentangled during the same task by parametrically varying these processes. During fMRI, participants maintained consonant letters in WM while sorting them in alphabetical order. Maintenance was investigated by varying the number of letters held in WM and manipulation by varying the number of moves required to sort the list alphabetically. The study yielded three main findings. First, the degree of both maintenance and manipulation demand had significant effects on behavior that were associated with different cortical regions: maintenance was associated with bilateral prefrontal and left parietal cortex, and manipulation with right parietal activity, a link that is consistent with the role of parietal cortex in symbolic computations. Second, univariate fMRI and tractography based on diffusion-weighted imaging showed that maintenance and manipulation regions are supported by two dissociable structural networks. Finally, maintenance and manipulation functional networks became increasingly segregated with increasing demand, possibly reflecting the protection of information held in WM from interference generated by manipulation operations. These results represent a novel approach to study the brain as an adaptive system that coordinates multiple ongoing cognitive processes.\n\nSignificance StatementDespite the importance of working memory (WM) in everyday life, little is known about how the brain is able to simultaneously maintain and manipulate information stored in short-term memory buffers. We examined evidence for two distinct, concurrent cognitive functions supporting maintenance and manipulation abilities by testing brain activity as participants performed a WM alphabetization task. We found behavioral and neural evidence in support of dissociable cognitive functions associated with these two operations. Furthermore, we found that connectivity between these networks was increasingly segregated as difficulty increased, and that this effect was positively related to individual WM ability. These results provide evidence that network segregation may act as a protective mechanism to enable successful performance under increasing WM demand.

neuroscience↗