Verbal working memory modulates afferent circuits in motor cortex

Verbal instruction and strategies informed by declarative memory are key to performance and acquisition of skilled actions. We previously demonstrated that anatomically distinct sensory–motor inputs converging on the corticospinal neurons of motor cortex are differentially sensitive to visual attention load. However, how loading of working memory shapes afferent input to motor cortex is unknown. This study used short‐latency afferent inhibition (SAI) to probe the effect of verbal working memory upon anatomically distinct afferent circuits converging on corticospinal neurons in the motor cortex. SAI was elicited by preceding a suprathreshold transcranial magnetic stimulus (TMS) with electrical stimulation of the median nerve at the wrist while participants mentally rehearsed a two‐ or six‐digit numeric memory set. To isolate different afferent intracortical circuits in motor cortex SAI was elicited, using TMS involving posterior–anterior (PA) or anterior–posterior (AP) monophasic current. Both PA and AP SAI were significantly reduced during maintenance of the six‐digit compared to two‐digit memory set. The generalized effect of working memory across anatomically distinct circuits converging upon corticospinal neurons in motor cortex is in contrast to the specific sensitivity of AP SAI to increased attention load. The common response across the PA and AP SAI circuits to increased working memory load may reflect an indiscriminate perisomatic mechanism involved in the voluntary facilitation of desired and/or suppression of unwanted actions during action selection or response conflict.Increasing the set size of digits to be maintained in working memory significantly reduced short‐latency afferent inhibition (SAI) in anatomically distinct circuits recruited by posterior–anterior (PA) and anterior–posterior (AP) transcranial magnetic stimulating (TMS) current. Loading of working memory decreases sensory afferent input across multiple intracortical circuits that converge upon corticospinal neurons in motor cortex.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/146615/1/ejn14154.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/146615/2/ejn14154_am.pd

Modulation of sensory processing during simultaneous bimodal stimulation: Effects of sensorimotor integration

Illusions such as the McGurk (McGurk and MacDonald, 1976) and ventriloquist (Radeau and Bertelson, 1974) effects or visual capture sensorimotor deficits (Holmes et al., 2004) demonstrate that our perception of and interaction with our environment is shaped by our ability to extract and integrate relevant sensory inputs across multiple modalities. Physiologically extraction occurs through a mechanism that facilitates relevant sensory representations and/or suppresses irrelevant ones within secondary sensory cortices, areas traditionally viewed as “modality-specific” cortex. This mechanism is commonly called “attention”. The purpose of the current thesis is to investigate the influence of motor requirements upon attentional modulation of sensory processing. It was hypothesized that different task demands associated with sensory processing for continuous movement rather than perception would result in earlier loci and/or different mechanisms of attentional modulation. Two studies used functional magnetic resonance imaging (fMRI) to investigate intermodal influences between a vibrotactile and visuospatial stimulus during a continuous sensorimotor task. These studies revealed that attention to vibrotactile stimulation guiding a continuous movement resulted in decreased activation in primary somatosensory cortex (S1) relative to when the same stimulus was an irrelevant distracter. This was regardless of the spatial or temporal properties of the two modalities. In a third study, somatosensory evoked potentials (SEPs) demonstrated that somatosensory processing is influenced as early as arrival to S1 from thalamic-cortical projections, however, SEPs did not demonstrate decreased activation during vibrotactile tracking. A fourth study using transcranial magnetic stimulation (TMS) confirmed differential excitability of S1 dependent upon whether the same sensory stimulus was used for perception or to guide a continuous sensorimotor transformation. Finally, a fifth study using behavioral measures demonstrated that the intramodal signal to noise ratio is an important factor in determining intermodal influence. This thesis provides insight into the influence of motor requirements upon sensory processing and demonstrates its importance in understanding how information is extracted from our environment. Understanding this has important implications for the interpretation/development of future work investigating intermodal influences upon sensory-processing

The effects of verbal and spatial working memory on short- and long-latency sensorimotor circuits in the motor cortex.

Multiple sensorimotor loops converge in the motor cortex to create an adaptable system capable of context-specific sensorimotor control. Afferent inhibition provides a non-invasive tool to investigate the substrates by which procedural and cognitive control processes interact to shape motor corticospinal projections. Varying the transcranial magnetic stimulation properties during afferent inhibition can probe specific sensorimotor circuits that contribute to short- and long-latency periods of inhibition in response to the peripheral stimulation. The current study used short- (SAI) and long-latency (LAI) afferent inhibition to probe the influence of verbal and spatial working memory load on the specific sensorimotor circuits recruited by posterior-anterior (PA) and anterior-posterior (AP) TMS-induced current. Participants completed two sessions where SAI and LAI were assessed during the short-term maintenance of two- or six-item sets of letters (verbal) or stimulus locations (spatial). The only difference between the sessions was the direction of the induced current. PA SAI decreased as the verbal working memory load increased. In contrast, AP SAI was not modulated by verbal working memory load. Visuospatial working memory load did not affect PA or AP SAI. Neither PA LAI nor AP LAI were sensitive to verbal or spatial working memory load. The dissociation of short-latency PA and AP sensorimotor circuits and short- and long-latency PA sensorimotor circuits with increasing verbal working memory load support multiple convergent sensorimotor loops that provide distinct functional information to facilitate context-specific supraspinal control

Glycerophospholipid Analysis of Optic Nerve Regeneration Models Indicate Potential Membrane Order Changes Associated with the Lipidomic Shifts

Optic nerve (ON) injury causes irreversible degeneration, leading to vision loss that cannot be restored with available therapeutics. Current therapies slow further degeneration but do not promote regeneration. New regenerative factors have been discovered that are successful . However, the mechanisms of efficient long-distance regeneration are still unknown. Membrane expansion by lipid insertion is an essential regenerative process, so lipid profiles for regenerating axons can provide insight into growth mechanisms. This article's analysis aims to add to the increasingly available ON regeneration lipid profiles and relate it to membrane order/properties. In this study, we present an analysis of glycerophospholipids, one of the largest axonal lipid groups, from three mammalian ON regeneration lipid profiles: Wnt3a, Zymosan + CPT-cAMP, and Phosphatase/Tensin homolog knockout (PTENKO) at 7 and 14 days post crush (dpc). Significant lipid classes, species, and ontological properties were crossreferenced between treatments and analyzed using Metaboanalyst 5.0 and Lipid Ontology (LION). Membrane order changes associated with significant lipid classes were evaluated by C-Laurdan dye and exogenous lipids provided to a neuroblastoma cell line. At 7 dpc, ONs show increased lysoglycerophospholipids and decreased phosphatidylethanolamines (PEs)/negative intrinsic curvature lipids. At 14 dpc, regenerative treatments show divergence: Wnt3a displays higher lysoglycerophospholipid content, while Zymosan and PTENKO decrease lysoglycerophospholipids and increase phosphatidylcholine (PC)-related species. Membrane order imaging indicates lysoglycerophospholipids decreases membrane order while PE and PC had no significant membrane order effects. Understanding these changes will allow therapeutic development targeting lipid metabolic pathways that can be used for vision loss treatments

C-Laurdan: Membrane Order Visualization of HEK293t Cells by Confocal Microscopy

Membrane order is a biophysical characteristic dependent on cellular lipid makeup. Cells regulate the membrane structure as it affects membrane-bound protein activity levels and membrane stability. Spatial organization of membrane lipids, such as lipid rafts, is a proposed theory that has been indirectly measured through polarity-sensitive fluorescent dyes. C-Laurdan is one such dye that penetrates plasma and internal membranes. C-Laurdan is excited by a single 405 nm photon and emits in two distinct ranges depending on membrane order. Herein, we present a protocol for staining HEK293t cells with C-Laurdan and acquiring ratiometric images using a revised ImageJ macro and confocal microscopy. An example figure is provided depicting the effects of methyl-β-cyclodextrin, known to remove lipid rafts through cholesterol sequestration, on HEK293t cells. Further image analysis can be performed through region of interest (ROI) selection tools

Analyses and Localization of Serotonin and L-DOPA in Ocular Tissues by Imaging Mass Spectrometry

Imaging mass spectrometry (IMS) allows for visualization of the spatial distribution of proteins, lipids, and other metabolites in a targeted or untargeted approach. The identification of compounds through mass spectrometry combined with the mapping of compound distribution in the sample establishes IMS as a powerful tool for metabolomics. IMS analysis for serotonin will allow researchers to pinpoint areas of deficiencies or accumulations associated with ocular disorders such as serotonin selective reuptake inhibitor optic neuropathy. Furthermore, L-DOPA has shown great promise as a therapeutic approach for disorders such as age-related macular degeneration, and IMS allows for localization, and relative magnitudes, of L-DOPA in the eye. We describe here an end-to-end approach of IMS from sample preparation to data analysis for serotonin and L-DOPA analysis

Analyses and Localization of Phosphatidylcholine and Phosphatidylserine in Murine Ocular Tissue Using Imaging Mass Spectrometry

Imaging mass spectrometry (IMS) allows for spatial visualization of proteins, lipids, and metabolite distributions in a tissue. Identifying these compounds through mass spectrometry, combined with mapping the compound distribution in the sample in a targeted or untargeted approach, renders IMS a powerful tool for lipidomics. IMS analysis for lipid species such as phosphatidylcholine and phosphatidylserine allows researchers to pinpoint areas of lipid deficiencies or accumulations associated with ocular disorders such as age-related macular degeneration and diabetic retinopathy. Here, we describe an end-to-end IMS approach from sample preparation to data analysis for phosphatidylcholine and phosphatidylserine analysis