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News Article | May 3, 2017
Site: phys.org

No two cakes smell identical, yet we are still able to recognise the general aroma that promises pleasure. Ayse Yarali from the Leibniz Institute for Neurobiology, Germany, explains that this ability to generalise a previously learned link between a cue - such as an odour - and an experience - such as a pleasant taste or the attack of a predator - to a range of similar cues can help us to ensure that we repeatedly encounter pleasant situations while avoiding risky ones. As the ability to generalise what is learned about a scent to a wide range of similar scents is an essential life skill for many species - including fruit flies - Yarali wondered whether the humble insect's ability to generalise changes over time. Teaming up with Christian König, Yarali decided to investigate how flies that had learned to associate an electric shock with a specific fruity odour reacted later when they experienced other fruity scents. Together they have discovered that fruit flies, which generalise memories across similar scents, do so more strongly after a period of time in much the same way as PTSD sufferers over generalise memories, and they publish their study in Journal of Experimental Biology. König and his colleagues Emmanuel Antwi-Adjei and Mathangi Ganesan identified three odours (3-octanol, n-amylacetate and 1-octen-3-ol) that could be distinguished by the fruit flies and used a Teflon tube lined with a pair of tightly wrapped copper coils attached to a power supply to shock the insects. 'If a fly happens to touch both of the coils with its legs - six legs give many possibilities - it gets an electric shock', explains Yarali. König then wafted one of the odours through the tube while the flies received a series of shocks in the hope that they would learn to avoid the odour in future. Twenty minutes later, König tested the insects' responses to the odour by placing them in a T-shaped maze where one arm was scented. Sure enough, the majority of flies avoided that region of the maze; they also recalled the memory 24 h later. But would the flies generalise the shocking experience and recall it when they encountered a similar, but different, odour? König replaced the odour in the T-maze with a new scent and, although some of the shocked flies avoided the novel scent 20 min later, it was a different matter after 24 h. This time, the flies' aversion to the new odour was as strong as their desire to avoid the odour that was directly associated with the shock. They had generalised their memory of the shock so that they recalled the memory even when the scent that they encountered was only vaguely familiar. So, flies can generalise a troubling memory across odours that smell similar. However, Yarali explains that even though the ability to generalise a memory can be beneficial, it can also become an impediment if it is exaggerated. 'Overly generalised memories of a traumatic experience in humans are one of the key behavioural hallmarks of post-traumatic stress disorder [PTSD]', explains Yarali; and the effects of human PTSD are often delayed, in much the same way that flies did not develop their general aversion to similar odours until several hours later. 'We cannot say that we have a fully fledged fly model of human PTSD', says Yarali, as the flies are unlikely to be suffering the same horrifying experiences that victims of PTSD endure, but they do appear to have at least one of the behavioural hallmarks of the human condition. And she is eager to discover whether the shocked flies exhibit some of the other behaviours that are indicative of a 'disturbed state of mind' with the hope that this research may one day help us to develop new therapeutic strategies for human sufferers of PTSD. Explore further: The precision of associative memories More information: König, C., Antwi-Adjei, E., Ganesan, M., Kilonzo, K., Viswanathan, V., Durairaja, A., Voigt, A. and Yarali, A. (2017). Aversive olfactory associative memory loses odor specificity over time. J. Exp. Biol. 220, 1548-1553., DOI: 10.1242/jeb.155317


Angenstein N.,Leibniz Institute for Neurobiology | Brechmann A.,Leibniz Institute for Neurobiology
NeuroImage | Year: 2013

Intensity and duration are important parameters for the processing of speech and music. Neuroimaging results on the processing of these parameters in tasks involving the discrimination of stimuli based on these parameters are controversial. Depending on the experimental approach, varying hypotheses on the involvement of the left and right auditory cortices (ACs) have been put forward. The aim of the present functional magnetic resonance imaging (fMRI) study was to find differences and commonalities in location and strength of brain activity during the processing of intensity and duration when the same stimuli have to be actively categorized according to these two parameters. For this we used a recently introduced method to determine lateralized processing in the AC with contralateral noise. Harmonic frequency modulated (FM) tone complexes were presented monaurally without and with contralateral noise. During categorization of the tones according to their intensity, contralateral noise increased activity mainly in the left AC, suggesting a special role for the left AC in this task. During categorization of tones according to their duration, contralateral noise increased activity in both the left and the right AC. This suggests that active categorization of FM tones according to their duration does not involve only the left AC as has been suggested, but also the right AC to a substantial degree. The area around Heschl's sulcus seems to be the most strongly involved during both intensity and duration categorization, albeit with different lateralization. Altogether the results of the present study support the view that the lateralized processing of the same stimuli in the human AC is strongly modulated by the given task (top-down effect). © 2013 Elsevier Inc.


Henschke J.U.,Leibniz Institute for Neurobiology | Noesselt T.,Leibniz Institute for Neurobiology | Scheich H.,Leibniz Institute for Neurobiology | Budinger E.,Leibniz Institute for Neurobiology
Brain structure & function | Year: 2015

Multisensory integration does not only recruit higher-level association cortex, but also low-level and even primary sensory cortices. Here, we will describe and quantify two types of anatomical pathways, a thalamocortical and a corticocortical that possibly underlie short-latency multisensory integration processes in the primary auditory (A1), somatosensory (S1), and visual cortex (V1). Results were obtained from Mongolian gerbils, a common model-species in neuroscience, using simultaneous injections of different retrograde tracers into A1, S1, and V1. Several auditory, visual, and somatosensory thalamic nuclei project not only to the primary sensory area of their own (matched) but also to areas of other (non-matched) modalities. The crossmodal output ratios of these nuclei, belonging to both core and non-core sensory pathways, vary between 0.4 and 63.5 % of the labeled neurons. Approximately 0.3 % of the sensory thalamic input to A1, 5.0 % to S1, and 2.1 % to V1 arise from non-matched nuclei. V1 has most crossmodal corticocortical connections, projecting strongest to S1 and receiving a similar amount of moderate inputs from A1 and S1. S1 is mainly interconnected with V1. A1 has slightly more projections to V1 than S1, but gets just faint inputs from there. Concerning the layer-specific distribution of the retrogradely labeled somata in cortex, V1 provides the most pronounced feedforward-type outputs and receives (together with S1) most pronounced feedback-type inputs. In contrast, A1 has most pronounced feedback-type outputs and feedforward-type inputs in this network. Functionally, the different sets of thalamocortical and corticocortical connections could underlie distinctive types of integration mechanisms for different modality pairings.


Panayotis N.,Weizmann Institute of Science | Karpova A.,Leibniz Institute for Neurobiology | Kreutz M.R.,Leibniz Institute for Neurobiology | Fainzilber M.,Weizmann Institute of Science
Trends in Neurosciences | Year: 2015

Local signaling events at synapses or axon terminals must be communicated to the nucleus to elicit transcriptional responses. The lengths of neuronal processes pose a significant challenge for such intracellular communication. This challenge is met by mechanisms ranging from rapid signals encoded in calcium waves to slower macromolecular signaling complexes carried by molecular motors. Here we summarize recent findings on macromolecular signaling from the synapse to the nucleus, in comparison to those employed in injury signaling along axons. A number of common themes emerge, including combinatorial signal encoding by post-translational mechanisms such as differential phosphorylation and proteolysis, and conserved roles for importins in coordinating signaling complexes. Neurons may integrate ionic flux with motor-transported signals as a temporal code for synaptic plasticity signaling. © 2014 Elsevier Ltd.


Ohl F.W.,Leibniz Institute for Neurobiology
Current Opinion in Neurobiology | Year: 2014

Rhythmic activity appears in the auditory cortex in both microscopic and macroscopic observables and is modulated by both bottom-up and top-down processes. How this activity serves both types of processes is largely unknown. Here we review studies that have recently improved our understanding of potential functional roles of large-scale global dynamic activity patterns in auditory cortex. The experimental paradigm of auditory category learning allowed critical testing of the hypothesis that global auditory cortical activity states are associated with endogenous cognitive states mediating the meaning associated with an acoustic stimulus rather than with activity states that merely represent the stimulus for further processing. © 2014.


Heine M.,Leibniz Institute for Neurobiology
Advances in Experimental Medicine and Biology | Year: 2012

The precision of signal transmission in chemical synapses is highly dependent on the structural alignment between pre- and postsynaptic components. The thermal agitation of transmembrane signaling molecules by surrounding lipid molecules and activity-driven changes in the local protein interaction affinities indicate a dynamic molecular traffic of molecules within synapses. The observation of local protein surface dynamics starts to be a useful tool to determine the contribution of intracellular and extracellular structures in organizing a plastic synapse. Local rearrangements by lateral diffusion in the synaptic and perisynaptic membrane induce fast density changes of signaling molecules and enable the synapse to change efficacy in short time scales. The degree of lateral mobility is restricted by many passive and active interactions inside and outside the membrane. AMPAR at the glutamatergic synapse are the best explored receptors in this respect and reviewed here as an example molecule. In addition, transsynaptic adhesion molecule complexes also appear highly dynamically in the synapse and do further support the importance of local surface traffic in subcellular compartments like synapses. © 2012 Springer-Verlag/WIen.


Angenstein N.,Leibniz Institute for Neurobiology | Brechmann A.,Leibniz Institute for Neurobiology
NeuroImage | Year: 2015

Intensity is an important parameter for the perception of complex auditory stimuli like speech. The results of previous studies on the processing of intensity are diverse since left-lateralized, right-lateralized and non-lateralized processing was suggested. A clear dependence of the lateralization on the kind of stimuli and/or task is not apparent. With the present functional magnetic resonance imaging (fMRI) study, we directly investigated the differences between a categorical and comparative task. To determine hemispheric involvement we used a method with contralateral noise presentation. Harmonic complexes were presented monaurally without and with contralateral noise. Both categorization and comparison of harmonic complexes according to their intensity more strongly involved the left than the right auditory cortex shown by a stronger effect of the additional noise on the activity in the left auditory cortex. Together with previous results, this suggests that left-lateralized processing of intensity in the auditory cortex can be observed independent of task and stimuli. The comparison task more strongly engaged the left auditory cortex than the categorization task probably due the additional need for sequential comparison and the right auditory cortex probably due to capacity reasons. Comparison also more strongly engaged areas associated with attentional processes and areas responsible for motor response selection. We suggest this to be caused by a more difficult response selection and by the need for continuous update of information in reference memory during the comparison task. © 2015 Elsevier Inc..


Tacikowski P.,Nencki Institute of Experimental Biology | Brechmann A.,Leibniz Institute for Neurobiology | Nowicka A.,Nencki Institute of Experimental Biology
Human Brain Mapping | Year: 2013

Previous neuroimaging studies have shown that the patterns of brain activity during the processing of personally relevant names (e.g., own name, friend's name, partner's name, etc.) and the names of famous people (e.g., celebrities) are different. However, it is not known how the activity in this network is influenced by the modality of the presented stimuli. In this fMRI study, we investigated the pattern of brain activations during the recognition of aurally and visually presented full names of the subject, a significant other, a famous person and unknown individuals. In both modalities, we found that the processing of self-name and the significant other's name was associated with increased activation in the medial prefrontal cortex (MPFC). Acoustic presentations of these names also activated bilateral inferior frontal gyri (IFG). This pattern of results supports the role of MPFC in the processing of personally relevant information, irrespective of their modality. © 2012 Wiley Periodicals, Inc.


Puschmann S.,Carl von Ossietzky University | Brechmann A.,Leibniz Institute for Neurobiology | Thiel C.M.,Carl von Ossietzky University
Human Brain Mapping | Year: 2013

Animal experiments provide evidence that learning to associate an auditory stimulus with a reward causes representational changes in auditory cortex. However, most studies did not investigate the temporal formation of learning-dependent plasticity during the task but rather compared auditory cortex receptive fields before and after conditioning. We here present a functional magnetic resonance imaging study on learning-related plasticity in the human auditory cortex during operant appetitive conditioning. Participants had to learn to associate a specific category of frequency-modulated tones with a reward. Only participants who learned this association developed learning-dependent plasticity in left auditory cortex over the course of the experiment. No differential responses to reward predicting and nonreward predicting tones were found in auditory cortex in nonlearners. In addition, learners showed similar learning-induced differential responses to reward-predicting and nonreward-predicting tones in the ventral tegmental area and the nucleus accumbens, two core regions of the dopaminergic neurotransmitter system. This may indicate a dopaminergic influence on the formation of learning-dependent plasticity in auditory cortex, as it has been suggested by previous animal studies. © 2012 Wiley Periodicals, Inc.


Ahmadi M.,University of Leicester | Quian Quiroga R.,University of Leicester | Quian Quiroga R.,Leibniz Institute for Neurobiology
NeuroImage | Year: 2013

We present an automatic denoising method based on the wavelet transform to obtain single trial evoked potentials. The method is based on the inter- and intra-scale variability of the wavelet coefficients and their deviations from baseline values. The performance of the method is tested with simulated event related potentials (ERPs) and with real visual and auditory ERPs. For the simulated data the presented method gives a significant improvement in the observation of single trial ERPs as well as in the estimation of their amplitudes and latencies, in comparison with a standard denoising technique (Donoho's thresholding) and in comparison with the noisy single trials. For the real data, the proposed method largely filters the spontaneous EEG activity, thus helping the identification of single trial visual and auditory ERPs. The proposed method provides a simple, automatic and fast tool that allows the study of single trial responses and their correlations with behavior. © 2012 Elsevier Inc.

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