Past events

Stimulus-specific adaptation is the decrease in the responses to a common stimulus that does not generalize, or generalize only partially, to other stimuli. Stimulus-specific adaptation in the auditory modality has been studied mostly with oddball sequences, which consist of a common and a rare stimuli. Recently, we started to use a number of other sound sequences in order to study the properties of adaptation in auditory cortex. I will show that (1) SSA is not only the result of the adaptation of the response to the common stimulus - in addition, the responses to the rare tones have a component due to the deviance of the rare tone relative to the regularity set by the common tone; (2) neuronal responses in auditory cortex of rats show sensitivity to finer types of statistical regularities; and (3) SSA can be evoked by other sounds as well, including sounds as similar to each other as two tokens of white noise. These results suggest the existence of a highly sensitive 'statistical machine' that analyzes and interprets the auditory scene.

The ability to anticipate and prepare in advance to changes in the environment is ascribed to neuronal systems in multi-cellular organisms. Yet by means of gene expression regulatory connectivity microbes too may have evolved to "anticipate" and prepare in advance. I will present evidence for microbial Pavlovian-like conditioning and discuss the similarities and differences to conditioning in the neuronal-cognitive context.

Whether we are speaking, swimming, or playing the piano, we are crucially dependent on our brain?s capacity to step through sequences of neural states. Songbirds provide a marvelous animal model in which to study this phenomenon. Their stereotyped vocalizations have hierarchical temporal structure spanning two orders or magnitude in timescale ? from individual vocal gestures lasting ten milliseconds, to song syllables (~100 msec), to song motifs (~1 sec). Several brain areas have been proposed to control timing at these different timescales. By manipulating these circuits with temperature change and observing the effect on song structure, we have been able to localize a single ?clock? circuit in the premotor vocal pathway. Intracellular neuronal recordings during singing elucidate the mechanism by which this clock circuit operates. Our findings are consistent with the predictions of a synfire-chain model? a synaptically connected chain of neurons in HVC. Our findings are inconsistent with models in which subthreshold dynamics, such as ramps or oscillations, play a role in the control of timing.

Neuro-plasticity is one of the key processes in our brain's physiology. This process allows our brain to change itself, functionally and structurally, following the acquisition of a new skill or experience. While functional aspects of neuro-plasticity can be studied using non-invasive techniques such as fMRI, EEF and MEG, investigation of the structural tissue characteristics of neuro-plasticity requires invasive histological approaches. Long-term experience necessitates structural plasticity which, in the adult brain, is characterized by changes in the shape and number of the synapses (synaptogenesis) as well as other process (neurogenesis, gliogenesis and white matter plasticity). Structural MRI studies of brain plasticity reveal significant volumetric changes via voxel-based morphometry of T1 weighted scans. Yet, the micro-structure correlates of these changes are not well understood. Diffusion tensor imaging (DTI) became one of the most popular imaging techniques in neuroimaging and is regarded as a micro-structural probe. Recently, tract-based spatial statistics (TBSS) analysis of DTI scans before and after long-term motor coordination training (juggling) revealed regional fractional anisotropy (FA) increase in parietal pathways. In that study, FA changes were reported following few weeks of training. An open question is what happens at shorter term learning and memory processes? In a short term spatial navigation study performed both in humans and rodents, we found that diffusion MRI can detect structural changes in cell morphology induced by plasticity within mere hours. Both in humans and rodents, the micro-structural changes, as observed by MRI, were localized to the anticipated brain regions: hippocampus, para-hippocampus, visual cortex, cingulate cortex and insular cortex. Our results indicate that significant structural occur in the tissue within mere hours - an interesting result by itself from the neurophysiological point of view. However, by investigating the induced structural changes both by histology and MRI it is possible to elucidate the relations between tissue micro-structure and the diffusion MRI signal. Preliminary results of such comparison indicate that in gray matter tissue one of cellular correlates of diffusion MRI indices is the density and shape of astrocyte. Indeed more studies should be directed