Biomedical subjects

Christiane Linster

Publications and source records attributed to Christiane Linster.

At least 19 recordsLinked to original sources

PubMed2006

Synaptic adaptation and odor-background segmentation.

Habituation is a form of non-associative memory that plays an important role in filtering stable or redundant inputs. The present study examines the contribution of habituation and cortical adaptation to odor-background segmentation. Segmentation of target odorants from background odorants is a fundamental computational requirement for the olfactory system. Recent electrophysiological data have shown that odor specific adaptation in piriform cortex neurons, mediated at least partially by synaptic adaptation between the olfactory bulb outputs and piriform cortex pyramidal cells, may provide an ideal mechanism for odor-background segmentation. This rapid synaptic adaptation acts as a filter to enhance cortical responsiveness to changing stimuli, while reducing responsiveness to static, potentially background stimuli. Using previously developed computational models of the olfactory system, we here show how synaptic adaptation at the olfactory bulb input to the piriform cortex, as demonstrated electrophysiologically, creates odor specific adaptation. We show how this known feature of olfactory cortical processing can contribute to adaptation to a background odor and to odor-background segmentation. We then show in a behavioral experiment that the odor-background segmentation is perceptually important and functions at the same time-scale as the synaptic adaptation observed between the olfactory bulb and cortex.

Adaptation, Physiological↗

PubMed2006

Role of centrifugal projections to the olfactory bulb in olfactory processing.

While there is evidence that feedback projections from cortical and neuromodulatory structures to the olfactory bulb are crucial for maintaining the oscillatory dynamics of olfactory bulb processing, it is not clear how changes in dynamics are related to odor perception. Using electrical lesions of the olfactory peduncle, sparing output from the olfactory bulb while decreasing feedback inputs to the olfactory bulb, we demonstrate here a role for feedback inputs to the olfactory bulb in the formation of odor-reward associations, but not for maintaining primary bulbar odor representations, as reflected by spontaneous odor discrimination.

Animals↗

PubMed2006

Broad activation of the olfactory bulb produces long-lasting changes in odor perception.

A number of electrophysiological experiments have shown that odor exposure alone, unaccompanied by behavioral training, changes the response patterns of neurons in the olfactory bulb. As a consequence of these changes, across mitral cells in the olfactory bulb, individual odors should be better discriminated because of previous exposure. We have previously shown that a daily 2-h exposure to odorants during 2 weeks enhances rats' ability to discriminate between chemically similar odorants. Here, we first show that the perception of test odorants is only modulated by enrichment with odorants that activate at least partially overlapping regions of the olfactory bulb. Second, we show that a broad activation of olfactory bulb neurons by daily local infusion of NMDA into both olfactory bulbs enhances the discrimination between chemically related odorants in a manner similar to the effect of daily exposure to odorants. Computational modeling of the olfactory bulb suggests that activity-dependent plasticity in the olfactory bulb can support the observed modulation in olfactory discrimination capability by enhancing contrast and synchronization in the olfactory bulb. Last, we show that blockade of NMDA receptors in the olfactory bulb impairs the effects of daily enrichment, suggesting that NMDA-dependent plasticity is involved in the changes in olfactory processing observed here.

Animals↗

PubMed2006

Olfactory enrichment improves the recognition of individual components in mixtures.

Odor mixtures can exhibit synthetic (the mixture is qualitatively different from its components) or elemental properties (the components are recognizable). We tested how prior olfactory enrichment affects the recognition of individual components in binary mixtures. Experimental rats were exposed to pairs of similar odors for one-hour periods twice daily over 20 days. Spontaneous discrimination between the binary mixture and the individual components of similar pairs of odors was tested before and after the odor enrichment. We found that, after the enrichment period, rats could discriminate components in binary mixtures that had not been discriminated prior to the enrichment period, and that this increase in discrimination capability was not always specific to the odorants used during the enrichment period.

Analysis of Variance↗

PubMed2006

Enrichment to odors improves olfactory discrimination in adult rats.

The authors tested how prior odor enrichment affects the spontaneous discrimination of both preexposed and novel odors. Experimental rats were exposed to single odors or to pairs of similar or dissimilar odors for 1-hr periods twice daily over 20 days. Spontaneous discriminations between pairs of similar odors were tested before and after the odor exposure period using an olfactory habituation task. The authors found that (a) experimental rats did not spontaneously discriminate similar odor pairs before the exposure period, whereas they spontaneously discriminated them after the enrichment period, and (b) the improvement of performance was not selective for the odors used during enrichment. These results show that odor experience changes perception in the manner predicted based on other groups' electrophysiological experiments.

Animals↗

PubMed2006

Dopamine D(2) receptor activation modulates perceived odor intensity.

Dopaminergic modulation affects odor detection thresholds and olfactory discrimination capabilities in rats. The authors show that dopamine D(2) receptor modulation affects odor discrimination capabilities in a manner similar to the modulation of stimulus intensity. Performance in a simultaneous odor discrimination task was systematically altered by manipulations of both odorant concentration and D(2) receptor activation (agonist quinpirole, 0.025-0.5 mg/kg; antagonist spiperone, 0.5 mg/kg). Rats' discrimination performance systematically improved at higher odor concentrations. Blockade of D(2) receptors improved performance equivalent to increasing odor concentration by 2 log units, whereas activation of D(2) receptors reduced odor discrimination performance in a dose-dependent manner. Bulbar dopamine release may serve a gain control function in the olfactory system, optimizing its sensitivity to changes in the chemosensory environment.

Analysis of Variance↗

PubMed2006

Cholinergic modulation in the olfactory bulb influences spontaneous olfactory discrimination in adult rats.

Cholinergic neuromodulation in the olfactory bulb has been hypothesized to regulate mitral cell molecular receptive ranges and the behavioral discrimination of similar odorants. We tested the effects of cholinergic modulation in the olfactory bulb of cannulated rats by bilaterally infusing cholinergic agents into the olfactory bulbs and measuring the rats' performances on separate spontaneous and motivated odor-discrimination tasks. Specifically, 6 microL/bulb infusions of vehicle (0.9% saline), the muscarinic antagonist scopolamine (7.6 mM and 38 mM), the nicotinic antagonist mecamylamine hydrochloride (3.8 mM and 19 mM), a combination of both antagonists, or the acetylcholinesterase inhibitor neostigmine (8.7 mM) were made 20 min prior to testing on an olfactory cross-habituation task or a rewarded, forced-choice odor-discrimination task. Spontaneous discrimination between chemically related odorants was abolished when nicotinic receptors were blocked in the olfactory bulb, and enhanced when the efficacy of cholinergic inputs was increased with neostigmine. Blocking muscarinic receptors reduced but did not abolish odor discrimination. Interestingly, no behavioral effects of modulating either nicotinic or muscarinic receptors were observed when rats were trained on a reward-motivated odor-discrimination task. Computational modeling of glomerular circuitry demonstrates that known nicotinic cholinergic effects on bulbar neurons suffice to explain these results.

Acetylcholine↗

PubMed2005

l-DOPA improves odor discrimination learning in rats.

Using a forced-choice odor discrimination task in rats, we show here that intraperitoneal injections of l-DOPA improve rats' odor discrimination performance in comparison to control rats injected with saline. Although the exact mechanism of l-DOPA and potential action on dopamine receptors remains unclear, the present results indicate that rats injected with the 20-50 mg/kg of l-DOPA performed significantly better in an odor discrimination task than did control rats. In addition, we observed a significant correlation between the concentration of l-DOPA and odor discrimination performance.

Animals↗

PubMed2005

Computation in the olfactory system.

Computational models are increasingly essential to systems neuroscience. Models serve as proofs of concept, tests of sufficiency, and as quantitative embodiments of working hypotheses and are important tools for understanding and interpreting complex data sets. In the olfactory system, models have played a particularly prominent role in framing contemporary theories and presenting novel hypotheses, a role that will only grow as the complexity and intricacy of experimental data continue to increase. This review will attempt to provide a comprehensive, functional overview of computational ideas in olfaction and outline a computational framework for olfactory processing based on the insights provided by these diverse models and their supporting data.

Action Potentials↗

PubMed2005

Computational modeling suggests that response properties rather than spatial position determine connectivity between olfactory glomeruli.

Olfactory responses require the representation of high-dimensional olfactory stimuli within the constraints of two-dimensional neural networks. We used a computational model of the honeybee antennal lobe to test how inhibitory interactions in the antennal lobe should be organized to best reproduce the experimentally measured input-output function in this structure. Our simulations show that a functionally organized inhibitory network, as opposed to an anatomically or all-to-all organized inhibitory network, best reproduces the input-output function of the antennal lobe observed with calcium imaging. In this network, inhibition between each pair of glomeruli was proportional to the similarity of their odor-response profiles. We conclude that contrast enhancement between odorants in the honeybee antennal lobe is best achieved when interglomerular inhibition is organized based on glomerular odor response profiles rather than on anatomical neighborhood relations.

Animals↗

PubMed2004

Opposing effects of D1 and D2 receptor activation on odor discrimination learning.

Dopaminergic modulation of cortical activity has been implicated in the formation of reward associations. There is abundant evidence for dopaminergic effects on olfactory processing. Using an olfactory discrimination task, the authors show that D1 and D2 dopamine receptors can regulate rats' olfactory discrimination capacities and that the effects of receptor activation functionally oppose one another. Injection of either the D1 agonist SKF 38393 (10 mg/kg) or the D2 antagonist spiperone (0.62 mg/kg) facilitated the discrimination of similar odorants but had no effect on the discrimination of dissimilar odorants, whereas both the D, antagonist SCH 23390 (0.025 mg/kg) and the D2 agonist quinpirole (0.2 mg/kg) significantly impaired rats' ability to discriminate similar and dissimilar odorants.

Animals↗

PubMed2003

Enhanced cholinergic suppression of previously strengthened synapses enables the formation of self-organized representations in olfactory cortex.

Computational modeling assists in analyzing the specific functional role of the cellular effects of acetylcholine within cortical structures. In particular, acetylcholine may regulate the dynamics of encoding and retrieval of information by regulating the magnitude of synaptic transmission at excitatory recurrent connections. Many abstract models of associative memory function ignore the influence of changes in synaptic strength during the storage process and apply the effect of these changes only during a so-called recall-phase. Efforts to ensure stable activity with more realistic, continuous updating of the synaptic strength during the storage process have shown that the memory capacity of a realistic cortical network can be greatly enhanced if cholinergic modulation blocks transmission at synaptic connections of the association fibers during the learning process. We here present experimental data from an olfactory cortex brain slice preparation showing that previously potentiated fibers show significantly greater suppression (presynaptic inhibition) by the cholinergic agonist carbachol than unpotentiated fibers. We conclude that low suppression of non-potentiated fibers during the learning process ensures the formation of self-organized representations in the neural network while the higher suppression of previously potentiated fibers minimizes interference between overlapping patterns. We show in a computational model of olfactory cortex, that, together, these two phenomena reduce the overlap between patterns that are stored within the same neural network structure. These results further demonstrate the contribution of acetylcholine to mechanisms of cortical plasticity. The results are consistent with the extensive evidence supporting a role for acetylcholine in encoding of new memories and enhancement of response to salient sensory stimuli.

Carbachol↗

PubMed2003

Configurational and nonconfigurational interactions between odorants in binary mixtures.

Studies on odor mixture perception suggest that although odor components can often be identified in mixtures, mixtures can also give rise to novel perceptual qualities that are not present in the components. Using an olfactory habituation task, the authors evaluated how the perceptual similarity between components in a mixture affects the perceptual quality of the mixture itself. Rats perceived binary mixtures composed of similar components as different from their 2 components, whereas binary mixtures composed of dissimilar components were perceived as very similar to their components. Results show that for both types of mixtures, pretraining to Component A reduces subsequent learning about Component B in rats trained in the presence of A.

Animals↗

PubMed2002

Spontaneous versus reinforced olfactory discriminations.

When the major response domains in the rat olfactory bulb that are evoked by odorant enantiomers are compared, some of these odorant pairs do not show significantly different activity patterns. Such pairs are not spontaneously discriminated in a behavioral test. We show here that even these similar odorants appear to evoke different activity patterns when every data point in a glomerular activity array is compared. These odorants also can be discriminated if they are subjected to differential reinforcement. These data suggest that the method chosen to assess olfactory discrimination will reveal different olfactory capabilities of rats. The small differences in glomerular activity that probably exist between any pair of odorants may serve as a basis for odor discrimination when rats are differentially reinforced, thereby establishing the remarkable limits of rat olfactory perception. At the same time, the major differences in glomerular responses appear to serve as the normal basis for spontaneous odor discrimination.

Administration, Inhalation↗

PubMed2002

Intramodal blocking between olfactory stimuli in rats.

The means by which olfactory systems enable the consistent recognition of biologically meaningful odors that may vary in composition over time is a central problem in olfaction. Experiments in honeybees have suggested a solution to one aspect of this problem by demonstrating that the learning of components in an odor mixture suppresses subsequent learning about additional components that are later added to that mixture. We here show, in rats, that intramodal olfactory blocking is also exhibited in vertebrates, and furthermore that the specific characteristics of this blocking are similar to those observed in intermodal blocking studies. Using an olfactory digging task, we submitted two groups of rats to the following olfactory training protocol: one group was first trained (five trials) on an odor (A), followed by five training trials on a binary mixture (A+B), while the second group was similarly trained on a different odor (C) followed by the binary mixture (A+B). After training, both groups' unrewarded responses to the mixture (A+B), odor (B), and an unconditioned control odor (X) were measured. For four out of five odor sets used in this experiment, a significant difference in digging time was observed between the responses of the two groups to odor B (P<.01), but not between their responses to the binary mixture (A+B) or to the control odor (X). These results demonstrate that pretraining rats with an odorant blocks subsequent learning about another odorant when the latter is presented simultaneously with the pretrained odorant, indicating that the components of a mixture are at least partially perceived as independent elements of this mixture.

Alcohols↗

PubMed2002

How synchronization properties among second-order sensory neurons can mediate stimulus salience.

Spatial patterns of glomerular activity in the vertebrate olfactory bulb and arthropod antennal lobe reflect an important component of first-order olfactory representation and contribute to odorant identification. Higher concentration odor stimuli evoke broader glomerular activation patterns, resulting in greater spatial overlap among different odor representations. However, behavioral studies demonstrate results contrary to what these data might suggest: Honeybees are more, not less, able to discriminate among odorants applied at higher concentrations. Using a computational model of the honeybee antennal lobe, the authors show that changes in synchronization patterns among antennal lobe projection neurons, as observed electrophysiologically, could parsimoniously underlie these observations. The results suggest that stimulus salience, as defined behaviorally, is directly correlated with the degree of synchronization among second-order olfactory neurons.

Animals↗

PubMed2002

Behavioral models of odor similarity.

Carbon chain length in several classes of straight-chain aliphatic odorants has been proposed as a model axis of similarity for olfactory research, on the basis of successes of studies in insect and vertebrate species. To assess the influence of task on measured perceptual similarities among odorants and to demonstrate that the systematic similarities observed within homologous odorant series are not task specific, the authors compare 3 different behavioral paradigms for rats (olfactory habituation, generalization, and discrimination). Although overall patterns of odorant similarity are consistent across all 3 of these paradigms, both quantitative measurements of perceptual similarity and comparability with 2-deoxyglucose imaging data from the olfactory bulb are dependent on the specific behavioral tasks used. Thus, behavioral indices of perceptual similarity are affected by task parameters such as learning and reward associations.

Animals↗

PubMedDate not supplied

Cholinergic modulation of sensory representations in the olfactory bulb.

We present a computational model of the mammalian olfactory bulb (OB) designed to investigate how cholinergic inputs modulate olfactory sensory representations. The model integrates experimental data derived from diverse physiological studies of cholinergic modulation of OB circuitry into a simulation of bulbar responses to realistic odorants. Experimentally-observed responses to a homologous series of odorants (unbranched aliphatic aldehydes) were simulated; realistic cholinergic inputs to the OB model served to increase the discriminability of the bulbar responses generated to very similar odorants. This simulation predicted, correctly, that missing cholinergic inputs to the OB would result in greater generalization between similar aliphatic aldehydes. Based on the assumption that the overlap between the neural representations of two sensory stimuli is predictive of their perceptual similarity, we tested this prediction in a behavioral experiments with rats. We show that, indeed, rats with selective lesions of cholinergic neurons that project to the OB and cortex discriminate less well between aliphatic aldehydes with similar carbon chain lengths than do rats that received sham lesions.

Animals↗