Tectonic Context and Possible Triggering of the 2019–2020 Puerto Rico Earthquake Sequence

An historically unprecedented seismic moment was released by crustal events of the 2019–2020 earthquake sequence near southwest Puerto Rico. The sequence involved at least two, and perhaps three interacting fault systems. The largest Mw 6.4 event was likely triggered by left lateral strike-slip events along the eastern extension of the North Boquerón Bay-Punta Montalva fault zone. The mainshock occurred in a normal fault zone that extends into a region where previous studies documented extensional deformation, beyond the Ponce fault and the Bajo Tasmanian fault. Coulomb stress changes by the mainshock may have triggered further normal-faulting aftershocks, left lateral strike-slip events in the region where these two fault zones interacted, and possibly right lateral strike-slip aftershocks along a third structure extending southward, the Guayanilla fault zone. Extension directions of the seismic sequence are consistently north-northwest–south-southeast-oriented, in agreement with the Global Navigation Satellite Systems-inferred motion direction of eastern Hispaniola relative to western Puerto Rico, and with crustal stress estimates for the overriding plate boundary zone.

The reverse motion illusion in random dot motion displays and implications for understanding development

Across two independent developmental labs, we have been puzzled by the observation that a small proportion of our child and adult participants consistently report perceiving motion in the direction opposite to that presented in random dot motion displays, sometimes even when the motion is at 100% coherence. In this review, we first draw together existing reports of misperceptions of motion direction in random dot displays across observers in a small percentage of trials, before reporting evidence of consistent reverse motion perception in a minority of observers, including previously unreported observations from our own studies of visual development. We consider possible explanations for this reverse motion illusion, including motion induction, motion energy, correspondence noise and spatial undersampling. However, more work is required to understand the individual differences relating to this percept. We suggest that errors in perceived motion direction are likely to be more widespread than can be currently gleaned from the literature and explain why systematic study is needed, especially in children. Finally, we list some remaining open questions and call for collaborative efforts to document this phenomenon and stimulate future investigation.

Concurrent fMRI demonstrates propagation of TMS effects across task-related networks

Transcranial magnetic stimulation (TMS) has become an important technique in both scientific and clinical practices, and yet our understanding of how the brain responds to TMS is still limited. Concurrent neuroimaging during TMS may bridge this gap, and emerging evidence suggests widespread that modulatory effects of TMS may be best captured through changes in functional connectivity between distributed networks, rather than local changes in cortical activity. However, the relationship between TMS stimulation parameters and evoked changes in functional connectivity is unknown. In this study, 24 healthy volunteers received concurrent TMS-fMRI while performing a dot-motion direction discrimination task. An MR-compatible coil was used to apply trains of three pulses at 10 Hz rTMS over the primary visual cortex (V1) at the onset of the dot stimuli with four levels of stimulation intensity (20%, 40%, 80%, and 120% of resting motor threshold, RMT). Behavioral results demonstrated impairment of motion discrimination at 80% RMT. FMRI results yielded three findings. First, functional connectivity between visual and non-visual areas increased as a function of rTMS intensity. Second, connectivity within the visual network was positively associated with motion accuracy, while the connectivity between visual and non-visual regions was negatively associated with motion accuracy. Lastly, we found that reductions in the similarity between functional and structural connectivity associated with increasing TMS intensity were constrained to the visual network. These findings demonstrate spatially dependent nonlinear effects of TMS intensity on brain functional connectivity that proceed beyond the site of stimulation and influence associated behavior.

Moving bar of light evokes vectorial spatial selectivity in the immobile rat hippocampus

Visual cortical neurons encode the position and motion direction of specific stimuli retrospectively, without any locomotion or task demand. Hippocampus, a part of visual system, is hypothesized to require self-motion or cognitive task to generate allocentric spatial selectivity that is scalar, abstract, and prospective. To bridge these seeming disparities, we measured rodent hippocampal selectivity to a moving bar of light in a body-fixed rat. About 70% of dorsal CA1 neurons showed stable activity modulation as a function of the bar angular position, independent of behavior and rewards. A third of tuned cells also encoded the direction of revolution. In other experiments, neurons encoded the distance of the bar, with preference for approaching motion. Collectively, these demonstrate visually evoked vectorial selectivity (VEVS). Unlike place cells, VEVS was retrospective. Changes in the visual stimulus or its trajectory did not cause remapping but only caused gradual changes. Most VEVS-tuned neurons behaved like place cells during spatial exploration and the two selectivities were correlated. Thus, VEVS could form the basic building block of hippocampal activity. When combined with self-motion, reward, or multisensory stimuli, it can generate the complexity of prospective representations including allocentric space, time, and episodes.

Pattern and component responses of primate MT neurons recorded with multi-contact electrodes, stimulated with 1D and 2D noise patterns.

Direction selective neurons in primary visual cortex (area V1) are affected by the aperture problem, i.e., they are only sensitive to motion orthogonal to their preferred orientation. A solution to this problem first emerges in the middle temporal (MT) area, where a subset of neurons (called pattern cells) combine motion information across multiple orientations and directions, becoming sensitive to pattern motion direction. These cells are expected to play a prominent role in subsequent neural processing, but they are intermixed with cells that behave like V1 cells (component cells), and others that do not clearly fall in either group. The picture is further complicated by the finding that cells that behave like pattern cells with one type of pattern, might behave like component cells for another. We recorded from macaque MT neurons using multi-contact electrodes while presenting both type I and unikinetic plaids, in which the components were 1D noise patterns. We found that the indices that have been used in the past to classify neurons as pattern or component cells work poorly when the properties of the stimulus are not optimized for the cell being recorded, as is always the case with multi-contact arrays. We thus propose alternative measures, which considerably ameliorate the problem, and allow us to gain insights in the signals carried by individual MT neurons. We conclude that arranging cells along a component-to-pattern continuum is an oversimplification, and that the signals carried by individual cells only make sense when embodied in larger populations.

Effect of Kinesiology Tape on Muscle Activation of Lower Extremity and Ankle Kinesthesia in Individuals With Unilateral Chronic Ankle Instability

Background: The purpose of the study was to determine the effect of kinesiology tape (KT) on lower limb muscle activation during computerized dynamic posturography (CDP) tasks and ankle kinesthesia in individuals with chronic ankle instability (CAI).Methods: Thirty-five men with CAI participated in this study. The experimental procedure followed a repeated measures design. Muscle activation of lower extremity and ankle kinesthesia of participants were measured using four taping treatments, namely, KT, athletic tape (AT), sham tape (ST), and no tape (NT) in a randomized order. Muscle activation was assessed using surface electromyography (sEMG) synchronized with CDP tests from seven lower extremity muscles of the unstable limb. Ankle kinesthesia was measured by using a threshold to detect the passive motion direction of the unstable ankle. Parameters were analyzed by using a one-way repeated measures ANOVA and followed by pairwise comparisons with a Bonferroni correction.Results: No significant difference was observed among different taping treatments for the majority of parameters during CDP. Except for condition 4 with open eyes, sway-referenced surface, and fixed surround in the sensory organization test (SOT), gastrocnemius medialis root mean square (RMS) was 28.19% lower in AT compared with NT (p = 0.021, 95% CI = 0.002–0.039), while gastrocnemius lateralis RMS was 20.25% lower in AT compared with KT (p = 0.038, 95% CI = 0.000–0.021). In forward-small sudden translation from motor control test (MCT), for peroneal longus (PL), RMS was 24.04% lower in KT compared with ST (p = 0.036, 95% CI = 0.000–0.018). In toes-down sudden rotation from adaption test (ADT), for PL, RMS was 23.41% lower in AT compared with ST (p = 0.015, 95% CI = 0.002–0.027). In addition, no significant difference was observed for a threshold to the detection of passive motion direction among different taping treatments.Conclusion: This study indicated that KT had minimal effect on the muscle activation of the unstable lower limb during static stance, self-initiated, and externally triggered perturbation tasks from CDP and ankle kinesthesia among individuals with CAI, suggesting that the benefit of KT was too small to be clinically worthwhile during application for CAI.

Task Demands Change Motion Information Coding in Area MT of the Macaque

Neurons in the primate Middle Temporal (MT) area signal information about visual motion and work together with the lateral prefrontal cortex (LPFC) to support memory-guided comparisons of visual motion direction. These areas are reciprocally connected and both contain neurons that signal visual motion direction in the strength of their responses. Previously, LPFC was shown to display marked changes in stimulus coding with altered task demands. Since MT and LPFC work together, we sought to determine if MT neurons display similar changes with heightened task demands. We hypothesized that heightened working-memory task demands would improve the task-relevant information and precipitate memory-related signals in MT. Here we show that engagement in a motion direction comparison task altered non-sensory activity and improved stimulus encoding by MT neurons. We found that this improvement in stimulus information transmission was largely due to preferential reduction in trial-to-trial variability within a sub-population of highly direction-selective neurons. We also found that a divisive normalization mechanism accounted for seemingly contradictory effects of task-demands on a heterogeneous population of neurons.

Perception of opposite-direction motion in random dot kinematograms

Computational models for motion perception suggest a possibility that read-out of motion signal can yield the perception of opposite direction of the true stimulus motion direction. However, this possibility was not obvious in a standard 2AFC motion discrimination (e.g., leftward vs.rightward). By allowing the motion direction to vary over 360° in typical random-dot kinematograms (RDKs) displays, and by asking observers to estimate the exact direction of motion, we were able to detect the presence of opposite-direction motion perception in RDKs.This opposite-direction motion perception was replicable across multiple display types andfeedback conditions, and participants had greater confidence in their opposite-direction responses than in true guess responses. When we fed RDKs into a computational model of motion processing, we found that the model estimated substantial motion activity in the direction opposite to the coherent stimulus direction, even though no such motion was objectively present in the stimuli, suggesting that the opposite-direction motion perception may be a consequenceof the properties of motion-selective neurons in visual cortex. Together, these results demonstrate that the perception of opposite-direction motion in RDKs is consistent with the known properties of the visual system.

Origins of direction selectivity in the primate retina

From mouse to primate, there is a striking discontinuity in our current understanding of the neural coding of motion direction. In non-primate mammals, directionally selective cell types and circuits are a signature feature of the retina, situated at the earliest stage of the visual process1,2. In primates, by contrast, direction selectivity is a hallmark of motion processing areas in visual cortex3,4, but has not been found in the retina, despite significant effort5,6. Here we combined functional recordings of light-evoked responses and connectomic reconstruction to identify diverse direction-selective cell types in the macaque monkey retina with distinctive physiological properties and synaptic motifs. This circuitry includes an ON-OFF ganglion cell type, a spiking, ON-OFF poly-axonal amacrine cell and the starburst amacrine cell, all of which show direction selectivity. Moreover, we found unexpectedly that macaque starburst cells possess a strong, non-GABAergic, antagonistic surround mediated by input from excitatory bipolar cells that is critical for the generation of radial motion sensitivity in these cells. Our findings open a new door to investigation of a novel circuitry that computes motion direction in the primate visual system.