Understanding how the brain changes its mind: microstimulation in the macaque frontal eye field reveals how saccade plans are changed

Accumulator models that integrate incoming sensory information into motor plans provide a robust framework to understand decision making. However, their applicability to situations that demand a change of plan raises an interesting problem for the brain. This is because interruption of the current motor plan must occur by a competing motor plan, which is necessarily weaker in strength. To understand how changes of mind get expressed in behavior, we used a version of the double-step task called the redirect task, in which monkeys were trained to modify a saccade plan. We microstimulated the frontal eye fields during redirect behavior and systematically measured the deviation of the evoked saccade from the response field to causally track the changing saccade plan. Further, to identify the underlying mechanisms, eight different computational models of redirect behavior were assessed. It was observed that the model that included an independent, spatially specific inhibitory process, in addition to the two accumulators representing the preparatory processes of initial and final motor plans, best predicted the performance and the pattern of saccade deviation profile in the task. Such an inhibitory process suppressed the preparation of the initial motor plan, allowing the final motor plan to proceed unhindered. Thus, changes of mind are consistent with the notion of a spatially specific, inhibitory process that inhibits the current inappropriate plan, allowing expression of the new plan.     

The use of a novel tablet application to quantify dysfunction in cervical spondylotic myelopathy patients

Background Context

Despite the prevalence and importance of myelopathy, there is a paucity of objective and quantitative clinical measures. The most commonly used diagnostic tools available are nonquantitative physical exam findings (eg, pathologic reflexes, and gait disturbance) and subjective scoring systems (eg, modified Japanese Orthopaedic Association [mJOA]). A decline in fine motor coordination is a hallmark of early myelopathy, which may be useful for quantitative testing.

Transperineal template‐guided mapping biopsy of the prostate

Accurate diagnosis of prostate cancer has eluded clinicians for decades. With our current understanding of prostate cancer, urologists should devise and confidently present the available treatment options – active surveillance/radical treatment/focal therapy to these patients. The diagnostic modalities used for prostate cancer have the dual problem of false negativity and overdiagnosis. Various modifications in the prostate biopsy techniques have increased the accuracy of cancer detection, but we are still far from an ideal diagnostic technique. Transperineal template‐guided mapping biopsy of the prostate is an exhaustive biopsy technique that has been improvised over the past decade, and has shown superior results to other available modalities. We have carried out a PubMed search on the available experiences on this diagnostic modality, and along with our own experiences, we present a brief review on transperineal template‐guided mapping biopsy of the prostate.     

Optical read-out and modulation of peripheral nerve activity

Numerous clinical and research applications necessitate the ability to interface with peripheral nerve fibers to read and control relevant neural pathways. Visceral organ modulation and rehabilitative prosthesis are two areas which could benefit greatly from improved neural interfacing approaches. Therapeutic neural interfacing, or ‘bioelectronic medicine', has potential to affect a broad range of disorders given that all the major organs of the viscera are neurally innervated. However, a better understanding of the neural pathways that underlie function and a means to precisely interface with these fibers are required. Existing peripheral nerve interfaces, consisting primarily of electrode-based designs, are unsuited for highly specific(individual axon) communication and/or are invasive to the tissue. Our laboratory has explored an optogenetic approach by which optically sensitive reporters and actuators are targeted to specific cell(axon) types. The nature of such an approach is laid out in this short perspective, along with associated technologies and challenges.     

Continuous Optical Monitoring of Cerebral Hemodynamics During Head-of-Bed Manipulation in Brain-Injured Adults

Introduction

Head-of-bed manipulation is commonly performed in the neurocritical care unit to optimize cerebral blood flow (CBF), but its effects on CBF are rarely measured. This pilot study employs a novel, non-invasive instrument combining two techniques, diffuse correlation spectroscopy (DCS) for measurement of CBF and near-infrared spectroscopy (NIRS) for measurement of cerebral oxy- and deoxy-hemoglobin concentrations, to monitor patients during head-of-bed lowering.

Methods

Ten brain-injured patients and ten control subjects were monitored continuously with DCS and NIRS while the head-of-bed was positioned first at 30° and then at 0°. Relative CBF (rCBF) and concurrent changes in oxy- (ΔHbO₂), deoxy- (ΔHb), and total-hemoglobin concentrations (ΔTHC) from left/right frontal cortices were monitored for 5 min at each position. Patient and control response differences were assessed.

Results

rCBF, ΔHbO₂, and ΔTHC responses to head lowering differed significantly between brain-injured patients and healthy controls (P < 0.02). For patients, rCBF changes were heterogeneous, with no net change observed in the group average (0.3 ± 28.2 %, P = 0.938). rCBF increased in controls (18.6 ± 9.4 %, P < 0.001). ΔHbO₂, ΔHb, and ΔTHC increased with head lowering in both groups, but to a larger degree in brain-injured patients. rCBF correlated moderately with changes in cerebral perfusion pressure (R = 0.40, P < 0.001), but not intracranial pressure.

Conclusion

DCS/NIRS detected differences in CBF and oxygenation responses of brain-injured patients versus controls during head-of-bed manipulation. This pilot study supports the feasibility of continuous bedside measurement of cerebrovascular hemodynamics with DCS/NIRS and provides the rationale for further investigation in larger cohorts.