Vestibular‐guided visual search

The amnesic symptoms that accompany vestibular dysfunction point to a functional relationship between the vestibular and visual memory systems. However, little is known about the underpinning cognitive processes. As a starting point, we sought evidence for a type of cross-modal interaction commonly observed between other sensory modalities in which the identification of a target (in this case, visual) is facilitated if earlier coupled to a unique, temporally coincident stimulus from another sensory domain (in this case, vestibular). Participants first performed a visual detection task in which stimuli appeared at random locations within a computerised grid. Unknown to participants, the onset of one particular stimulus was accompanied by a brief, sub-sensory pulse of galvanic vestibular stimulation (GVS). Across two visual search experiments, both old and new targets were identified faster when presented in the grid location at which the GVS-paired visual stimulus had appeared in the earlier detection task. This location advantage appeared to be based on relative rather than absolute spatial co-ordinates since the effect held when the search grid was rotated 90°. Together these findings indicate that when individuals return to a familiar visual scene (here, a 2D grid), visual judgements are facilitated when targets appear at a location previously associated with a unique, task-irrelevant vestibular cue. This novel case of multisensory interplay has broader implications for understanding how vestibular signals inform cognitive processes and helps constrain the growing therapeutic application of GVS

The Modulation of Visual Spatial Memory by Galvanic Vestibular Stimulation

It is now widely accepted that the vestibular system not only affects autonomic motor function but cognitive function too, most notably visuospatial learning and memory. While many studies have explored this association from a biological perspective, few have done so from a psychological one. The aim of this thesis was to identify a possible psychological mechanism by which the vestibular system specifically interacts with spatial memory processes. Artificially stimulating the vestibular system via trans-mastoidal galvanic current (aka GVS) provides a controlled means by which this vestibular-visual spatial interaction can be explored. In a previous study, we showed that search for a location of a 2-D static visual target was facilitated when that target location was initially encoded with in the presence of a brief, subsensory galvanic signal (L. Smith, Gkioka & Wilkinson, 2020). In Chapter 2, I replicated this GVS advantage in new 2-D visual arrays, showing that temporally co-incident vestibular activation can facilitate visual search and spatial memory in subsequent encounters of that same 2-D spatial representation presented during encoding. Chapter 3 explored whether this cross-modal priming would hold in a dynamic 3-D virtual environment, in which external landmarks were manipulated (present/absent) to test whether the GVS priming is dependent on the location of the target relative to other visual stimuli. The GVS prime was more effective in the presence of visual landmarks, whereby participants chose direct routes more frequently and navigated to the target location with higher accuracy. Finally in Chapter 4, I demonstrated that these beneficial priming effects were also evident in people with dementia who showed visuo-spatial short-term memory impairment. Together these studies suggest that the human brain can make use of momentary vestibular signals to help individuate the encoding of visuospatial memories. The results also provide justification for trialling the therapeutic effects of GVS in amnestic populations

Vestibular-Guided Visual Search

Two experimental studies exploring the impact of galvanic vestibular stimulation on visual search

Experiment 2 – Visual search for GVS targets in upright versus rotated orientation

Reaction time and accuracy responses from participants who took part in experiment 2

Experiment 1 – Visual Search for GVS-Paired Visual Stimuli

Reaction time and accuracy responses from participants who took part in experiment 1

Serum-Soluble CD163 Levels as a Prognostic Biomarker in Patients with Diffuse Large B-Cell Lymphoma Treated with Chemoimmunotherapy

The majority of patients with Diffuse Large B-cell Lymphoma (DLBCL) will respond to first-line treatment and be cured. However, the disease is heterogeneous, and biomarkers able to discriminate patients with suboptimal prognosis are needed. M2 CD163-positive tumor-associated macrophages (TAMs) were shown to be implicated in DLBCL disease activity regulation. Serum-soluble CD163 (sCD163) functions as a scavenger receptor for haptoglobin–hemoglobin complexes and is mostly expressed by monocytes and macrophages. Its levels are used to determine macrophage activation. We aimed to determine serum sCD163 in a sample of DLBCL patients and study eventual correlations with parameters of disease activity or survival. Serum sCD163 levels were measured in 40 frozen sera from patients diagnosed with DLBCL and 30 healthy individuals (HIs) using an enzyme-linked immunosorbent assay (ELISA). Statistical analyses were performed using SPSS version 28. The results showed that patients who achieved complete response after standard-of-care immunochemotherapy and were alive and disease-free after 12 months of follow-up but had elevated sCD163 levels (above median) at diagnosis presented a significantly worse overall survival compared to those with initial serum sCD163 levels below the median (p = 0.03). Consequently, serum sCD163 levels in patients with DLBCL may constitute a marker of long-term response to chemoimmunotherapy