9. Understanding the P300 and Its Components in a Three-Stimulus Visual Oddball Task

The P300 is an electrical signal that is a neural correlate of prediction error and surprise. Recent studies show the P300 is made of distinct subcomponents that correlate with cognitive mechanisms the brain uses in responding to the unexpected. The P3A component is generated in the frontal region of the brain, an area associated with attention and cognitive control, in response to novel irrelevant stimuli. Conversely, the P3B component is generated in the parietal region, a brain area that is active during encounters that involve learning and memory, in response to novel task-relevant stimuli. Our experiment explores these signals using a visual three-stimulus oddball paradigm in which frequent non-target stimuli occur with 80% probability, novel irrelevant stimuli 10%, and novel task-relevant stimuli 10%. We record electrical signals from the brain with scalp electroencephalography (EEG) while subjects complete the oddball task, allowing us to examine neural responses to three types of stimuli. Based on a context-updating theory that the brain responds to an unexpected stimulus by making comparisons to prior expectations, we expect to observe a robust P300 effect with a frontal P3A in response to novel irrelevant stimuli, indicating higher demands on attention and effortful processing. We also expect novel task relevant stimuli to produce a parietal P3B, showing activity related to working memory. Exploring these signals allows further understanding of how the brain processes unexpected information with varying demands on attention and memory. Keywords: P300, P3A, P3B, electroencephalography (EEG), visual oddball, context updating, attention, working memor

Ultrasonic-aided fabrication of gold nanofluids

A novel ultrasonic-aided one-step method for the fabrication of gold nanofluids is proposed in this study. Both spherical- and plate-shaped gold nanoparticles (GNPs) in the size range of 10-300 nm are synthesized. Subsequent purification produces well-controlled nanofluids with known solid and liquid contents. The morphology and properties of the nanoparticle and nanofluids are characterized by transmission electron microscopy, scanning electron microscope, energy dispersive X-ray spectroscope, X-ray diffraction spectroscopy, and dynamic light scattering, as well as effective thermal conductivities. The ultrasonication technique is found to be a very powerful tool in engineering the size and shape of GNPs. Subsequent property measurement shows that both particle size and particle shape play significant roles in determining the effective thermal conductivity. A large increase in effective thermal conductivity can be achieved (approximately 65%) for gold nanofluids using plate-shaped particles under low particle concentrations (i.e.764 μM/L)

Structural modulation of the biological activity of gold nanoparticles functionalized with a carbonic anhydrase inhibitor

Gold nanoparticles (AuNPs) have gained attention for their potential and application in different fields, e.g. nanomedicine. This study explores the surface functionalization of AuNP with inhibitors of carbonic anhydrases (CAs, EC 4.2.1.1). Some CA transmembrane isoforms have been recognized as therapeutic targets for the treatment of hypoxic tumors. Embedding a CA inhibitory function onto a nanosized unit has been proved to enable selective targeting of transmembrane isoforms. We report the preparation in aqueous media, the characterization and CA inhibition tests of AuNPs coated with a sulfonamide (SA) derivative, already known for its inhibitory activity toward CAs. The physico-chemical characterization of SA-coated AuNPs was performed with a combination of scattering and spectroscopic techniques. We detect a threshold effect of the SA concentration on the final hydrodynamic and core sizes of the capped nanoparticles and on their stability over aggregation. These modified nanoparticles were assayed for inhibition of some CA transmembrane isoforms (CA IX and XII) as well as of two cytosolic isoforms (CA I and II), and show interesting inhibitory efficiency in the submicromolar range and some selectivity for transmembrane isoforms