Anterior Cingulate Cortex Causally Supports Meta-Learning.

In dynamic environments with volatile rewards the anterior cingulate cortex (ACC) is believed to determine whether a visual object is relevant and should be chosen. The ACC may achieve this by integrating reward information over time to estimate which objects are worth to explore and which objects should be avoided. Such a higher-order meta-awareness about which objects should be explored predicts that the ACC causally contributes to choices when the reward values of objects are unknown and must be inferred from ongoing exploration. We tested this suggestion in nonhuman primates using a learning task that varied the number of object features that could be relevant, and by controlling the motivational value of choosing objects. During learning the ACC was transiently micro-stimulated when subjects foveated the to-be-chosen stimulus. We found that stimulation selectively impaired learning when feature uncertainty and motivational value of choices were high, which was linked to a deficit in using reward outcomes for feature-specific credit assignment. Application of an adaptive reinforcement learning model confirmed a primary deficit in weighting prediction errors that led to a meta-learning impairment to adaptively increase exploration during learning and to an impaired use of working memory to support learning. These findings provide causal evidence that the reward history traces in ACC are essential for meta-adjusting the exploration-exploitation balance and the strength of working memory of object values during adaptive behavior.

Generating Patient-Specific Acoustic Simulations for Transcranial Focused Ultrasound Procedures Based on Optical Tracking Information.

Optical tracking is a real-time transducer positioning method for transcranial focused ultrasound (tFUS) procedures, but the predicted focus from optical tracking typically does not incorporate subject-specific skull information. Acoustic simulations can estimate the pressure field when propagating through the cranium but rely on accurately replicating the positioning of the transducer and skull in a simulated space. Here, we develop and characterize the accuracy of a workflow that creates simulation grids based on optical tracking information in a neuronavigated phantom with and without transmission through an ex vivo skull cap. The software pipeline could replicate the geometry of the tFUS procedure within the limits of the optical tracking system (transcranial target registration error (TRE): 3.9 ± 0.7 mm). The simulated focus and the free-field focus predicted by optical tracking had low Euclidean distance errors of 0.5±0.1 and 1.2±0.4 mm for phantom and skull cap, respectively, and some skull-specific effects were captured by the simulation. However, the TRE of simulation informed by optical tracking was 4.6±0.2, which is as large or greater than the focal spot size used by many tFUS systems. By updating the position of the transducer using the original TRE offset, we reduced the simulated TRE to 1.1 ± 0.4 mm. Our study describes a software pipeline for treatment planning, evaluates its accuracy, and demonstrates an approach using MR-acoustic radiation force imaging as a method to improve dosimetry. Overall, our software pipeline helps estimate acoustic exposure, and our study highlights the need for image feedback to increase the accuracy of tFUS dosimetry.

Anterior cingulate cortex causally supports flexible learning under motivationally challenging and cognitively demanding conditions.

Anterior cingulate cortex (ACC) and striatum (STR) contain neurons encoding not only the expected values of actions, but also the value of stimulus features irrespective of actions. Values about stimulus features in ACC or STR might contribute to adaptive behavior by guiding fixational information sampling and biasing choices toward relevant objects, but they might also have indirect motivational functions by enabling subjects to estimate the value of putting effort into choosing objects. Here, we tested these possibilities by modulating neuronal activity in ACC and STR of nonhuman primates using transcranial ultrasound stimulation while subjects learned the relevance of objects in situations with varying motivational and cognitive demands. Motivational demand was indexed by varying gains and losses during learning, while cognitive demand was varied by increasing the uncertainty about which object features could be relevant during learning. We found that ultrasound stimulation of the ACC, but not the STR, reduced learning efficiency and prolonged information sampling when the task required averting losses and motivational demands were high. Reduced learning efficiency was particularly evident at higher cognitive demands and when subjects experienced loss of already attained tokens. These results suggest that the ACC supports flexible learning of feature values when loss experiences impose a motivational challenge and when uncertainty about the relevance of objects is high. Taken together, these findings provide causal evidence that the ACC facilitates resource allocation and improves visual information sampling during adaptive behavior.

Peroneus Quartus Muscle.

The peroneus quartus (PQ) muscle is a rare but sometimes missed potential etiology of ankle pain and tendon subluxation. We report the case of a 16-year-old boy who presented with lateral right ankle pain and subluxation of peroneal tendons. He had a history of non-Hodgkin lymphoma and palpable distal fibular osteochondroma. Seven months after excision of the exostosis and repair of the peroneal tendon retinaculum, the pain recurred. Imaging showed a split peroneus brevis (PB) tendon. During surgery, a PQ muscle was found and excised, and the PB tendon was repaired. One year after surgery, the patient's symptoms were resolved.

Neurectomy Outcomes in Patients With Morton Neuroma: Comparison of Plantar vs Dorsal Approaches.

BACKGROUND: Morton neuroma is a compressive neuropathy of the plantar digital nerve. Several surgical approaches have been used to treat painful Morton neuroma, with each approach having distinct advantages and disadvantages. For this study, we used validated outcome assessment tools to retrospectively compare patient satisfaction with 2 approaches. METHODS: The medical records and survey responses of 37 patients with 42 neuromas were evaluated with respect to outcomes and patient satisfaction after neurectomies performed through either a plantar or dorsal surgical approach by one Ochsner Clinic Foundation attending physician. Outcomes were evaluated using the 36-Item Short Form Health Survey (SF-36) and the Foot Function Index (FFI) self-assessments. RESULTS: Twenty patients underwent neurectomy through a dorsal approach, and 17 patients underwent neurectomy through a plantar approach. We found no statistically significant differences between the dorsal and plantar approach groups with respect to outcomes and patient satisfaction as measured by the SF-36 or the FFI. CONCLUSION: This study supports the use of either the plantar or dorsal approach for the resection of Morton neuroma and suggests that a plantar approach for neurectomy can produce satisfactory results.

Ultrasound-guided popliteal sciatic nerve blockade in the severely and morbidly obese: a prospective and randomized study.

PURPOSE: Limited research data exist regarding optimal block techniques in the severely and morbidly obese patient population. We compared two approaches to sciatic nerve blockade at the popliteal fossa in severely and morbidly obese patients. The purpose of this study was to identify differences in pain scores, block onset characteristics, and adverse events between the proximal (prebifurcation) and the distal (postbifurcation) sites. METHODS: Patients with a body mass index ≥35 scheduled for unilateral foot surgery with a popliteal block were randomized to receive an ultrasound-guided popliteal block proximal or distal to the bifurcation of the sciatic nerve. The primary endpoint was numerical rating scale (NRS) scores in the post anesthesia care unit (PACU). RESULTS: Thirty patients were enrolled in each group for a total of 60 participants. Patients in the distal group had lower NRS scores upon entry into the PACU (0.70 ± 1.91) compared with the proximal group (2.17 ± 3.37), had a faster onset of sensorimotor blockade, and were less likely to require a repeat block procedure, conversion to general anesthesia, or local anesthetic supplementation by the surgical team. There was no difference in block procedure times or incidence of nerve injury between the two groups. CONCLUSIONS: The distal approach to the popliteal block provided several intraoperative and analgesic benefits without a difference in block procedural times in the severely and morbidly obese. It is a cost-free intervention that results in a higher likelihood of a successful block in a population where avoidance of opioids is desirable.