No abstract

Attention improves the encoding of visual stimuli. One mechanism that is implicated in facilitating sensory encoding is the firing of action potentials in bursts. We tested the hypothesis that when spatial attention is directed to a stimulus, this causes an increase in burst firing to the attended stimulus. To the contrary, we found an attention-dependent reduction in burstiness among putative pyramidal neurons in macaque area V4. We accounted for this using a conductance-based Hodgkin-Huxley style model in which attentional modulation stems from scaling excitation and inhibition. The model exhibited attention-dependent increases in firing rate and made the surprising and correct prediction that when attention is directed into a neuron’s receptive field, this reduces action potential height. The model thus provided a unified explanation for three distinct forms of attentional modulation, two of them novel, and implicates scaling of the responses of excitatory and inhibitory input populations in mediating attention.

This review describes the synthetic routes to various types of organic polymeric monoliths. Significant concentration is applied to the role of these continuous, porous structures in both heterogeneous catalysis and biocatalysis. A monolith is composed of a solitary mass filled with interconnected pores, which include both large flow‐through pores and smaller meso‐ or micropores. These porous monolithic materials have several advantages over conventional packed beds of porous polymeric beads, owing to their macroporosity and lack of interstitial spacing. Their large pores contribute to mass transfer, which allows the structure to withstand higher back pressures than conventional packed beds, whereas their small pores still operate by diffusion. The effect of multiple parameters, such as the temperature, the cross‐link density, and the type and content of porogenic solvent on the pore formation and pore size distribution is outlined for monoliths prepared through free radical polymerization and ring‐opening metathesis polymerization (ROMP). Post‐functionalization of these monoliths to control the surface chemistry of the supports and/or affix functional catalysts is elucidated, as well as employment of these supports in continuous catalytic reactions. Significant advances in supported catalysis for metathesis, Heck, Suzuki, Sonogashira–Hagihara, and biocatalytic reactions are described.

One of the most well established forms of attentional modulation is an increase in firing rate when attention is directed into a neuron’s receptive field. The degree of rate modulation, however, can vary considerably across individual neurons, especially among broad spiking neurons (putative pyramids). We asked whether this heterogeneity might be correlated with a neuronal response property that is used in intracellular recording studies to distinguish among distinct neuronal classes: the burstiness of the neuronal spike train. We first characterized the burst spiking behavior of V4 neurons and found that this varies considerably across the population, but did not find evidence for distinct classes of burst behavior. Burstiness did, however, vary more widely across the class of neurons that show the greatest heterogeneity in attentional modulation, and within that class, burstiness helped account for differences in attentional modulation. Among these broad spiking neurons, rate modulation was largely restricted to bursty neurons, which as a group showed a highly significant increase in firing rate with attention. Further, every bursty broad spiking neuron whose firing rate was significantly modulated by attention exhibited an increase in firing rate. In contrast, non-bursty broad spiking neurons exhibited no net attentional modulation, and while some individual neurons did show significant rate modulation, these were divided among neurons showing increases and decreases. These findings show that macaque Area V4 shows a range of bursting behavior, and that the heterogeneity of attentional modulation can be explained, in part, by variation in burstiness.