Diverse Time Encoding Strategies Within the Medial Premotor Areas of the Primate.

The measurement of time in the subsecond scale is critical for many sophisticated behaviors, yet its neural underpinnings are largely unknown. Recent neurophysiological experiments from our laboratory have shown that the neural activity in the medial premotor areas (MPC) of macaques can represent different aspects of temporal processing. During single interval categorization, we found that preSMA encodes a subjective category limit by reaching a peak of activity at a time that divides the set of test intervals into short and long. We also observed neural signals associated with the category selected by the subjects and the reward outcomes of the perceptual decision. On the other hand, we have studied the behavioral and neurophysiological basis of rhythmic timing. First, we have shown in different tapping tasks that macaques are able to produce predictively and accurately intervals that are cued by auditory or visual metronomes or when intervals are produced internally without sensory guidance. In addition, we found that the rhythmic timing mechanism in MPC is governed by different layers of neural clocks. Next, the instantaneous activity of single cells shows ramping activity that encodes the elapsed or remaining time for a tapping movement. In addition, we found MPC neurons that build neural sequences, forming dynamic patterns of activation that flexibly cover all the produced interval depending on the tapping tempo. This rhythmic neural clock resets on every interval providing an internal representation of pulse. Furthermore, the MPC cells show mixed selectivity, encoding not only elapsed time, but also the tempo of the tapping and the serial order element in the rhythmic sequence. Hence, MPC can map different task parameters, including the passage of time, using different cell populations. Finally, the projection of the time varying activity of MPC hundreds of cells into a low dimensional state space showed circular neural trajectories whose geometry represented the internal pulse and the tapping tempo. Overall, these findings support the notion that MPC is part of the core timing mechanism for both single interval and rhythmic timing, using neural clocks with different encoding principles, probably to flexibly encode and mix the timing representation with other task parameters.

Amodal population clock in the primate medial premotor system for rhythmic tapping.

The neural substrate for beat extraction and response entrainment to rhythms is not fully understood. Here we analyze the activity of medial premotor neurons in monkeys performing isochronous tapping guided by brief flashing stimuli or auditory tones. The population dynamics shared the following properties across modalities: the circular dynamics of the neural trajectories form a regenerating loop for every produced interval; the trajectories converge in similar state space at tapping times resetting the clock; and the tempo of the synchronized tapping is encoded in the trajectories by a combination of amplitude modulation and temporal scaling. Notably, the modality induces displacement in the neural trajectories in the auditory and visual subspaces without greatly altering the time-keeping mechanism. These results suggest that the interaction between the medial premotor cortex's amodal internal representation of pulse and a modality-specific external input generates a neural rhythmic clock whose dynamics govern rhythmic tapping execution across senses.

The amplitude in periodic neural state trajectories underlies the tempo of rhythmic tapping.

Our motor commands can be exquisitely timed according to the demands of the environment, and the ability to generate rhythms of different tempos is a hallmark of musical cognition. Yet, the neuronal underpinnings behind rhythmic tapping remain elusive. Here, we found that the activity of hundreds of primate medial premotor cortices (MPCs; pre-supplementary motor area [preSMA] and supplementary motor area [SMA]) neurons show a strong periodic pattern that becomes evident when their responses are projected into a state space using dimensionality reduction analysis. We show that different tapping tempos are encoded by circular trajectories that travelled at a constant speed but with different radii, and that this neuronal code is highly resilient to the number of participating neurons. Crucially, the changes in the amplitude of the oscillatory dynamics in neuronal state space are a signature of duration encoding during rhythmic timing, regardless of whether it is guided by an external metronome or is internally controlled and is not the result of repetitive motor commands. This dynamic state signal predicted the duration of the rhythmically produced intervals on a trial-by-trial basis. Furthermore, the increase in variability of the neural trajectories accounted for the scalar property, a hallmark feature of temporal processing across tasks and species. Finally, we found that the interval-dependent increments in the radius of periodic neural trajectories are the result of a larger number of neurons engaged in the production of longer intervals. Our results support the notion that rhythmic timing during tapping behaviors is encoded in the radial curvature of periodic MPC neural population trajectories.

Conversion of failed Roux-en-Y gastric bypass to biliopancreatic diversion with duodenal switch: outcomes of 9 case series.

INTRODUCTION: Weight regain after Roux-en-Y gastric bypass (RYGB) is a frustrating long-term complication in some patients. Revision of RYGB to biliopancreatic diversion with duodenal switch (BPD-DS) is an appealing option. There is a paucity of information in literature regarding this type of conversion. SETTING: Regional referral center and teaching hospital, Pennsylvania, United States; nonprofit. METHODS: Between 2013 and 2016, a retrospective chart review was performed on all our revision cases. Patients who underwent conversion from RYGB to BPD-DS were selected and analyzed. RESULTS: Conversion from RYGB to BPD-DS was performed on 9 patients (8 females, 1 male; mean age: 49.2±7.6 [36-61] years). The mean body mass index (BMI) before the initial RYGB was 54.2±14.2 (36.2-79) kg/m2. The lowest mean BMI reached before conversion was 33.9±6.2 (27.9-43.3) kg/m2 before it increased to 45.6±8.7 (28.8-60.2) corresponding to excess weight loss (EWL) of 33.1%±17.7% (10.6%-68.1%), before conversion. The average operative time was 402.6±65.8 (328-515) minutes for 1-stage conversions. No morbidities, reoperation, or readmission over 30 days postoperatively were reported. No leaks or mortalities were identified. The mean duration of follow-up postconversion is 16.3±13.6 (3-42) months. After conversion surgery, the mean BMI was 35.8±8.2 (27.6-49.5) kg/m2, while mean EWL loss was 64.1%±18.8% (45.9%-88.7%). The BMI of the cohort decreased by a mean of 9.8±5.1 (0.5-16.8) and the EWL increased by 31%±23.1% (4%-76.6%). CONCLUSION: Our results indicate that conversion of failed RYGB to BPD-DS is laparoscopically or robotically safe and effective. A large cohort study with long-term follow-up is necessary to further assess the safety and efficacy of this method.

Laparoscopic repair of duodenal atresia in a low birth weight neonate.

The small volume of the infant abdomen limits the application of laparoscopic procedures. We successfully repaired a duodenal atresia in a 2-kg female infant using a standard diamond-shaped anastomosis and intracorporeal suturing and knot-tying techniques. Anesthesia and positive pressure ventilation assured adequate gas exchange during pneumoperitoneum during the procedure.