Past events

Repetitive transcranial magnetic stimulation (rTMS) has been shown to induce neurophysiological changes in the cortex that can be recorded through electroencephalography. Oscillatory activity in the gamma (30-50 Hz) frequency range represents a neurophysiological process that has been shown to be altered during working memory, a cognitive process that is mediated by the dorsolateral prefrontal cortex (DLPFC). We examined the effect of 20 Hz rTMS applied bilaterally to the DLPFC on gamma oscillations elicited during the N-back working memory task in 22 healthy subjects and 24 patients with schizophrenia. Patients with SCZ then continued to receive rTMS (active or sham) for an additional 4 weeks (i.e., 20 treatments in total). Compared to sham rTMS, active rTMS produced a significant increase in gamma oscillations in healthy subjects that was most pronounced in the 3-back condition, the condition associated with greatest cognitive demand. In patients with schizophrenia, by contrast, active rTMS reduced gamma oscillations compared to sham. Neither group demonstrated significant changes in other frequency ranges, suggesting that rTMS selectively modulates only gamma oscillations. In addition, after an additional 4 weeks of active rTMS evidence suggests a potentiation of N-back performance compared to sham but no significant changes in negative symptoms. These findings suggest that patients with schizophrenia demonstrate altered gamma modulation which may be normalized in response to rTMS and over time translate into improved cognitive performance. These findings may also provide important insights into the mechanisms that lead to enhanced cognitive performance.

A fundamental question in systems neuroscience is: What are the organization principles of human visual cortex? Visual cortex originates in primary visual cortex and extends through a hierarchy of early, intermediate, and high-level visual regions separated across two processing streams (dorsal and ventral). While much is known about the organization of early visual cortex, much less is known about the organization of high-level visual regions in the ventral stream, which are thought to be involved in visual recognition. Current theories suggest functional distinctions between early and high-level regions in the ventral processing stream: early and intermediate visual regions contain a systematic representation of the visual field across a series of multiple maps (Wandell and Winawer, 2011), whereas higher-level regions are thought to be specialized for processing specific types of stimuli such as objects, faces, body parts, words, and places (Kanwisher, 2010). Several alternative theories suggest other principles for the organization of the ventral stream, including expertise (Tarr and Gauthier, 2000), eccentricity biases (Malach et al., 2002), or distributed representations (Haxby et al., 2001; Kriegeskorte et al., 2008). Nevertheless, two notions are common to these theories. First, it is widely accepted that different rules underlie the functional organization of high-level and early visual cortex. Second, the profile of activations in high-level visual cortex is thought to be more variable across individuals compared to early visual cortex. Contrary to the prevailing view, we propose common organization principles throughout early and high-level visual cortex, where functional regions have consistent anatomical locations and preserved spatial relationships to neighboring regions as well as retinotopic maps. Employing these principles enables the first framework for consistent parcellation of high-level visual regions, which can also be applied to other sensory and nonsensory cortical systems.

In my talk I will present a generalized view of dendritic function in neocortical pyramidal neurons summarizing a decade of research. Later I will present two yet unpublished works. The first will describe dendritic integration in layer 4 spiny stellate neurons and the role of dendritic spikes in-vivo. The second work will present coding of texture in layer 2-3 neurons in the rat barrel cortex using two photon imaging methods.