An Updated Midline Rule: Visual Callosal Connections Anticipate Shape and Motion in Ongoing Activity across the Hemispheres

It is generally thought that callosal connections (CCs) in primary visual cortices serve to unify the visual scenery parted in two at the vertical midline (VM). Here, we present evidence that this applies also to visual features that do not cross yet but might cross the VM in the future. During reversible deactivation of the contralateral visual cortex in cats, we observed that ipsilaterally recorded neurons close to the border between areas 17 and 18 receive selective excitatory callosal input on both ongoing and evoked activity. In detail, neurons responding well to a vertical Gabor patch moving away from the deactivated hemifield decreased prestimulus and stimulus-driven activity much more than those preferring motion toward the cooled hemifield. Further, activity of neurons responding to horizontal lines decreased more than the response to vertical lines. Embedding a single Gabor into a collinear line context selectively stabilized responses, especially when the context was limited to the intact hemifield. These findings indicate that CCs interconnect not only neurons coding for similar orientations but also for similar directions of motion. We conclude that CCs anticipate stimulus features that are potentially relevant for both hemifields (i.e., coherent motion but also collinear shape) because already prestimulus activity and activity to stimuli not crossing the VM revealed feature specificity. Finally, we hypothesize that intrinsic and callosal networks processing different orientations and directions are anisotropic close to the VM facilitating perceptual grouping along likely future motion or (shape) trajectories before the visual stimulus arrives

Gamma-Rhythmic Gain Modulation

Cognition requires the dynamic modulation of effective connectivity, i.e., the modulation of the postsynaptic neuronal response to a given input. If postsynaptic neurons are rhythmically active, this might entail rhythmic gain modulation, such that inputs synchronized to phases of high gain benefit from enhanced effective connectivity. We show that visually induced gamma-band activity in awake macaque area V4 rhythmically modulates responses to unpredictable stimulus events. This modulation exceeded a simple additive superposition of a constant response onto ongoing gamma-rhythmic firing, demonstrating the modulation of multiplicative gain. Gamma phases leading to strongest neuronal responses also led to shortest behavioral reaction times, suggesting functional relevance of the effect. Furthermore, we find that constant optogenetic stimulation of anesthetized cat area 21a produces gamma-band activity entailing a similar gain modulation. As the gamma rhythm in area 21a did not spread backward to area 17, this suggests that postsynaptic gamma is sufficient for gain modulation

Copy Number Variation in Patients with Disorders of Sex Development Due to 46,XY Gonadal Dysgenesis

Disorders of sex development (DSD), ranging in severity from mild genital abnormalities to complete sex reversal, represent a major concern for patients and their families. DSD are often due to disruption of the genetic programs that regulate gonad development. Although some genes have been identified in these developmental pathways, the causative mutations have not been identified in more than 50% 46,XY DSD cases. We used the Affymetrix Genome-Wide Human SNP Array 6.0 to analyse copy number variation in 23 individuals with unexplained 46,XY DSD due to gonadal dysgenesis (GD). Here we describe three discrete changes in copy number that are the likely cause of the GD. Firstly, we identified a large duplication on the X chromosome that included DAX1 (NR0B1). Secondly, we identified a rearrangement that appears to affect a novel gonad-specific regulatory region in a known testis gene, SOX9. Surprisingly this patient lacked any signs of campomelic dysplasia, suggesting that the deletion affected expression of SOX9 only in the gonad. Functional analysis of potential SRY binding sites within this deleted region identified five putative enhancers, suggesting that sequences additional to the known SRY-binding TES enhancer influence human testis-specific SOX9 expression. Thirdly, we identified a small deletion immediately downstream of GATA4, supporting a role for GATA4 in gonad development in humans. These CNV analyses give new insights into the pathways involved in human gonad development and dysfunction, and suggest that rearrangements of non-coding sequences disturbing gene regulation may account for significant proportion of DSD cases

Plant ecology meets animal cognition: impacts of animal memory on seed dispersal

We propose that an understanding of animal learning and memory is critical to predicting the impacts of animals on plant populations through processes such as seed dispersal, pollination and herbivory. Focussing on endozoochory, we review the evidence that animal memory plays a role in seed dispersal, and present a model which allows us to explore the fundamental consequences of memory for this process. We demonstrate that decision-making by animals based on their previous experiences has the potential to determine which plants are visited, which fruits are selected to be eaten from the plant and where seeds are subsequently deposited, as well as being an important determinant of animal survival. Collectively, these results suggest that the impact of animal learning and memory on seed dispersal is likely to be extremely important, although to date our understanding of these processes suffers from a conspicuous lack of empirical support. This is partly because of the difficulty of conducting appropriate experiments but is also the result of limited interaction between plant ecologists and those who work on animal cognition

Der Einfluss kortiko-kortikaler Verbindungen auf die Antworteigenschaften von Neuronen im primären visuellen Kortex

In dieser Studie untersuchten wir den Einfluss von interhemisphärischen Projektionen auf die Antworteigenschaften von Neuronen in den Zielregionen dieser Verbindungen. Dazu wurden elektrophysiologische Ableitungen in den Arealen 17 und 18 bei der anästhesierten Katze durchgeführt. Wir kombinierten diese Ableitungen mit der reversiblen, thermischen Deaktivierung der kallosal projizierenden Neurone auf der kontralateralen Hemisphäre. Unsere Ergebnisse zeigten eine stimulusspezifische Modulation der Aktionspotentialrate, wobei exzitatorische Einflüsse von der anderen Hemisphäre dominierten. Diese Effekte konnten für statische und dynamische Stimuli, sowie für spontane Hirnaktivität beobachtet werden. Weiterhin konnten wir zeigen, dass der Mechanismus der Ratenänderung einer multiplikativen Skalierung folgt, was umso ausgeprägter war, je größer die Ratenänderungen ausfielen. Die Orientierungsselektivität wurde nur wenig durch die kallosalen Verbindungen beeinflusst. Für Neurone die eine additive Skalierung ihre Rate zeigten, konnten wir jedoch im Mittel eine Änderung der Tuningbreite, und damit Selektivität, dieser Zellen nachweisen. Zusätzlich zur mittleren Aktionspotentialrate und Tuningbreite quantifizierten wir die Variabilität der neuronalen Antworten. Hier konnten wir eine stimulusabhängige Modulation der Antwortvariabilität durch die kallosalen Verbindungen feststellen. Es zeigte sich, dass eine verminderte Antwortvariabilität vor allem bei denjenigen Neuronen auftrat, die eine Erhöhung ihrer Aktionspotentialrate durch die Kühldeaktivierung erfuhren. Die Art der Variabilitätsänderung sprach für eine Beeinflussung spontaner Zustandsänderungen des kortikalen Netzwerks durch die kallosalen Verbindungen. Unsere Ergebnisse komplementieren bestehende Arbeiten zu der Funktionsweise kortiko-kortikaler Verbindungen, und geben, zum ersten Mal, eine ausführliche mathematische Beschreibung ihrer Mechanismen. Es ist zu betonen, dass unsere Ergebnisse in vivo, und damit möglichst nahe an der natürlichen Arbeitsweise des Gehirns gewonnen wurden. Nimmt man an, dass sich die am kallosalen System gewonnenen Erkenntnisse auf andere kortiko-kortikale Verbindungen übertragen lassen, haben unsere Ergebnisse interessante Implikationen für zukünftige Modelle neuronaler Codierung und Verarbeitung