Astronomers and physicists noticed centuries ago that visual spatial resolution is higher for dark than light stimuli, but the neuronal mechanisms for this perceptual asymmetry remain unknown. Here we demonstrate that the asymmetry is caused by a neuronal nonlinearity in the early visual pathway. We show that neurons driven by darks (OFF neurons) increase their responses roughly linearly with luminance decrements, independent of the background luminance. However, neurons driven by lights (ON neurons) saturate their responses with small increases in luminance and need bright backgrounds to approach the linearity of OFF neurons. We show that, as a consequence of this difference in linearity, receptive fields are larger in ON than OFF thalamic neurons, and cortical neurons are more strongly driven by darks than lights at low spatial frequencies. This ON/OFF asymmetry in linearity could be demonstrated in the visual cortex of cats, monkeys, and humans and in the cat visual thalamus. Furthermore, in the cat visual thalamus, we show that the neuronal nonlinearity is present at the ON receptive field center of ONcenter neurons and ON receptive field surround of OFF-center neurons, suggesting an origin at the level of the photoreceptor. These results demonstrate a fundamental difference in visual processing between ON and OFF channels and reveal a competitive advantage for OFF neurons over ON neurons at low spatial frequencies, which could be important during cortical development when retinal images are blurred by immature optics in infant eyes.neuronal coding | lateral geniculate nucleus | area V1 | irradiation illusion | LFP L ight and dark stimuli are separately processed by ON and OFF channels in the retina and visual thalamus. Surprisingly, although most textbooks assume that ON and OFF visual responses are balanced throughout the visual system, recent studies have identified a pronounced overrepresentation of the OFF visual responses in primary visual cortex (area V1) (1-3). This recent discovery resonates with pioneering studies by Galilei (4) and von Helmholtz (5) who noticed that visual spatial resolution was higher for dark than light stimuli. Galilei (4) related the difference in resolution to the observation that a light patch on a dark background appears larger than the same sized dark patch on a light background, an illusion that von Helmholtz (5) named the "irradiation illusion." Although this illusion has been studied in the past (6, 7), its underlying neuronal mechanisms remain unknown. It has been suggested that the perceived size differences could be caused by the light scatter in the optics of the eye followed by a neuronal nonlinearity (6, 7), but there are no neuronal measurements of a nonlinearity that fits the explanation. Previous studies revealed differences in response linearity between ON and OFF retinal ganglion cells (8, 9) and horizontal cells (10). However, a main conclusion from these studies was that ON retinal ganglion cells were roughly linear and less rectified than OFF retinal gangl...
Arrays of graphene solution‐gated field‐effect transistors are fabricated for the detection of electrical activity of electrogenic cells. Cardiomyocyte‐like cells are cultured on the transistor arrays and their action potentials are detected by the underlying transistors. The analysis of the recorded cell signals and the electronic noise of the transistors confirm that graphene transistors surpass state‐of‐the‐art devices for bioelectronic applications.
We present a new biocompatible nanostructured microelectrode array for extracellular signal recording from electrogenic cells. Microfabrication techniques were combined with a template-assisted approach using nanoporous aluminum oxide to develop gold nanopillar electrodes. The nanopillars were approximately 300-400 nm high and had a diameter of 60 nm. Thus, they yielded a higher surface area of the electrodes resulting in a decreased impedance compared to planar electrodes. The interaction between the large-scale gold nanopillar arrays and cardiac muscle cells (HL-1) was investigated via focused ion beam milling. In the resulting cross-sections we observed a tight coupling between the HL-1 cells and the gold nanostructures. However, the cell membranes did not bend into the cleft between adjacent nanopillars due to the high pillar density. We performed extracellular potential recordings from HL-1 cells with the nanostructured microelectrode arrays. The maximal amplitudes recorded with the nanopillar electrodes were up to 100% higher than those recorded with planar gold electrodes. Increasing the aspect ratio of the gold nanopillars and changing the geometrical layout can further enhance the signal quality in the future.
This contribution adopts the taxonomic concept annotation and alignment approach. Accordingly, and where indicated, previous and newly inferred meanings of taxonomic names are individuated according to one specific source. Articulations among these concepts and pairwise, logically consistent alignments of original and revisionary classifications are also provided, in addition to conventional nomenclatural provenance information. A phylogenetic revision of the broad-nosed weevil genera Minyomerus Horn, 1876 sec. O’Brien & Wibmer (1982), and Piscatopus Sleeper, 1960 sec. O’Brien & Wibmer (1982) (Curculionidae [non-focal]: Entiminae [non-focal]: Tanymecini [non-focal]) is presented. Prior to this study, Minyomerus sec. O’Brien & Wibmer (1982) contained seven species, whereas the monotypic Piscatopus sec. O’Brien & Wibmer (1982) was comprised solely of Piscatopus griseus Sleeper, 1960 sec. O’Brien & Wibmer (1982). We thoroughly redescribe these recognized species-level entities and furthermore describe ten species as new to science: Minyomerus bulbifrons sec. Jansen & Franz (2015) (henceforth: [JF2015]), sp. n., Minyomerus aeriballux [JF2015], sp. n., Minyomerus cracens [JF2015], sp. n., Minyomerus gravivultus [JF2015], sp. n., Minyomerus imberbus [JF2015], sp. n., Minyomerus reburrus [JF2015], sp. n., Minyomerus politus [JF2015], sp. n., Minyomerus puticulatus [JF2015], sp. n., Minyomerus rutellirostris [JF2015], sp. n., and Minyomerus trisetosus [JF2015], sp. n. A cladistic analysis using 46 morphological characters of 22 terminal taxa (5/17 outgroup/ingroup) yielded a single most-parsimonious cladogram (L = 82, CI = 65, RI = 82). The analysis strongly supports the monophyly of Minyomerus [JF2015] with eight unreversed synapomorphies, and places Piscatopus griseus sec. O’Brien & Wibmer (1982) within the genus as sister to Minyomerus rutellirostris [JF2015]. Accordingly, Piscatopus sec. Sleeper (1960), syn. n. is changed to junior synonymy of Minyomerus [JF2015], and its sole member Piscatopus griseus sec. Sleeper (1960) is moved to Minyomerus [JF2015] as Minyomerus griseus [JF2015], comb. n. In addition, the formerly designated type Minyomerus innocuus Horn, 1876 sec. Pierce (1913), syn. n. is changed to junior synonymy of Minyomerus microps (Say, 1831) [JF2015] which has priority. The genus is widespread throughout western North America, ranging from Canada to Mexico and Baja California. Apparent patterns of interspecific diversity of exterior and genitalic morphology, varying host plant ranges, overlapping and widely extending species distributions, suggest an early origin for Minyomerus [JF2015], with a diversification that likely followed the development of North American desert biomes. Three species in the genus – i.e., Minyomerus languidus Horn, 1876 [JF2015], Minyomerus microps [JF2015], and Minyomerus trisetosus [JF2015] – are putatively considered parthenogenetic.
The brain infers our spatial orientation and properties of the world from ambiguous and noisy sensory cues. Judging self-motion (heading) in the presence of independently moving objects poses a challenging inference problem because the image motion of an object could be attributed to movement of the object, self-motion, or some combination of the two. We test whether perception of heading and object motion follows predictions of a normative causal inference framework. In a dual-report task, subjects indicated whether an object appeared stationary or moving in the virtual world, while simultaneously judging their heading. Consistent with causal inference predictions, the proportion of object stationarity reports, as well as the accuracy and precision of heading judgments, depended on the speed of object motion. Critically, biases in perceived heading declined when the object was perceived to be moving in the world. Our findings suggest that the brain interprets object motion and self-motion using a causal inference framework.
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