Biomedical subjects

Alfredo Fontanini

Publications and source records attributed to Alfredo Fontanini.

7 recordsLinked to original sources

PubMed2006

State-dependent modulation of time-varying gustatory responses.

Sensory processing is modulated by attention, which is a function of network states. Here we show that changes in such states do more than a simple gating of stimuli: they actually re-arrange cortical coding space to emphasize emotional valences. We delivered taste stimuli to rats before and after a spontaneous state change ("disengagement") that is associated with a reduction in attention and a concurrent emergence of cortical mu rhythms. The percentage of cortical neurons that responded to tastes, and the average response across neurons, remained stable with disengagement, but the particulars of the responses changed drastically. The distinctiveness of sucrose and quinine-which represent the high and low ends of the palatability spectrum-increased, the distinctiveness of the two aversive tastes (quinine and citric acid) decreased, and the distinctiveness of sucrose and NaCl, which were almost identically palatable to start with, did not change. Overall, then, the changes appeared to be palatability-specific. Two additional findings were consistent with this conclusion: rats' palatability-related behavioral responses to the tastes changed in similar ways with disengagement and disengagement-related neural changes specifically appeared late in the response, when palatability-specific information emerges in cortical responses. These data suggest that neural state changes can change the content of neural codes.

Action Potentials↗

PubMed2006

Gustatory processing: a dynamic systems approach.

Recent gustatory studies have provided a growing body of evidence that taste processing is dynamic and distributed, and the taste system too complex to be adequately described by traditional feed-forward models of taste coding. Current research demonstrates that neuronal responses throughout the gustatory neuroaxis are broad, variable and temporally structured, as a result of the fact that the taste network is extensive and heavily interconnected, containing modulatory pathways, many of which are reciprocal. Multimodal influences (e.g. olfactory and somatosensory) and effects of internal state (e.g. attention and expectation), shown in both behavioral and neuronal responses to taste stimuli, add further complexity to neural taste responses. Future gustatory research should extend to more brain regions, incorporate more connections, and analyze behaviors and neuronal responses in both time- and state-dependent manners.

Animals↗

PubMed2006

Slow-waves in the olfactory system: an olfactory perspective on cortical rhythms.

Over the past few years, it has become clear that oscillatory dynamics of cortical networks are closely involved in sensory coding, attention, memory and sleep. Although most experimental and theoretical studies have focused on the neocortex, we believe that progress in understanding cortical oscillations can be advanced by also considering the olfactory system--which shares many basic properties with the neocortex and shows similar oscillatory patterns. Besides offering the advantage of a greater experimental tractability, the olfactory cortex might prove to be instrumental in uncovering general functional principles of neocortical oscillations, by virtue of the potentially important role of olfaction during neocortical evolution. In this article, we illustrate how such an evolution-based comparative approach can provide novel insights into neocortical slow-wave sleep oscillations and their relationship to respiration.

Animals↗

PubMed2005

Variable coupling between olfactory system activity and respiration in ketamine/xylazine anesthetized rats.

In this study, we have characterized slow and fast oscillations at several stages of olfactory processing under light and deep ketamine/xylazine anesthesia in the albino rat. While monitoring the animal's respiration, we also obtained field potentials from the olfactory bulb and piriform (olfactory) cortex and simultaneously recorded membrane potentials in piriform cortex pyramidal cells. Our results demonstrate that oscillations are generally found at higher frequencies under lighter and lower frequencies under deeper anesthesia. In previous studies of cerebral cortex, similar results in ketamine/xylazine anesthetized animals have been interpreted to correspond with the higher frequencies found during waking and lower frequencies found in the sleep state. Correlation and coherence analysis between data obtained in the bulb and cortex reveals a clear difference in coupling depending on the anesthetic state of the animal. Specifically, activity recorded in the whole system is highly correlated with respiration during deep anesthesia, whereas only the olfactory bulb, and not the cortex, is correlated with respiration during light anesthesia. These data suggest that global activity in the piriform cortex is actually more directly tied to peripheral slow respiratory input during slow wave than fast wave states and that the coupling between olfactory structures can be dynamically modulated by the level of anesthesia and therefore presumably by different brain states as well.

Analgesics↗

PubMed2004

7 to 12 Hz activity in rat gustatory cortex reflects disengagement from a fluid self-administration task.

The 7 to 12 Hz rhythm is a high-voltage oscillatory phenomenon recorded in many rat neocortical regions, largely analogous to the rodent and human somatosensory mu rhythm. Central to any interpretation of the functional significance of this pattern is the analysis of the behavioral context associated with it. Much of the debate on the function of mu, variously believed to represent either an environment-oriented or -isolated state, has relied primarily on its association with quiet immobility. In this report, we describe the relationship between the 7 to 12 Hz rhythm and a more complex behavioral setting, in which we were able to dissociated task orientation from disengagement. We trained head-restrained, water-restricted rats to perform a simple variant of a timed fluid self-administration task, while recording local field potentials from gustatory cortex (GC). Rats progressed through two behavioral states that were clearly distinguishable on the basis of lever-pressing regimes: a task-oriented state and a second state that reflected disengagement from the task. Concurrent GC neural recordings revealed bilaterally coherent oscillations in the 7 to 12 Hz range associated solely with the latter state. Consistent with published recordings of mu rhythm from somatosensory cortex, these rhythmic episodes were endogenously quenched when the rats prepared to lever-press; this inhibition of rhythmic episodes lasted through fluid delivery and consumption, making it clear that GC rhythms are not related to gustatory processing itself. By showing a direct relationship between the 7 to 12 Hz rhythm and disengagement from a task, these data provide strong and novel evidence that this gustatory rhythm in rats is associated with withdrawal from experimental contingencies.

Action Potentials↗

PubMed2003

Ketamine-xylazine-induced slow (< 1.5 Hz) oscillations in the rat piriform (olfactory) cortex are functionally correlated with respiration.

The occurrence of low frequency (<1.5 Hz) cerebral cortical oscillations during slow-wave sleep has recently lead to the suggestion that this pattern of activity is specifically associated with conditions in which the brain is mostly closed to external inputs and running on its own. In the current experiments, we used a combination of in vivo intracellular and extracellular field potential recordings obtained under conditions of ketamine-xylazine anesthesia to examine slow-wave behavior in the olfactory system. We demonstrate the occurrence of low-frequency oscillations in field potentials of both the olfactory bulb and cortex and in the membrane potentials of cortical pyramidal cells. By monitoring ongoing breathing, we also show that these oscillations are all correlated with the natural breathing cycle. Using a tracheotomized preparation, we demonstrate that slow oscillatory patterns could occasionally be produced even when air is no longer entering the nose, supporting the view that the olfactory system has an intrinsic propensity to oscillate. However, in the case of tracheotomized rats, the amplitude and regularity of the oscillations as well as their patterns of correlation are disrupted. All temporal relationships were restored when air was pulsed into the nostrils. We conclude that, in the olfactory system of freely breathing rats, there is a strong relationship between the occurrence and timing of slow oscillations and the ongoing periodic sensory input resulting from respiration. This coupling between olfactory cortex slow oscillations and respiration may result from the interaction between respiratory-related rhythmic input and the tendency for olfactory structures to oscillate intrinsically. We believe this finding has important functional as well as evolutionary implications.

Animals↗

PubMedDate not supplied

Temporary basolateral amygdala lesions disrupt acquisition of socially transmitted food preferences in rats.

Lesions of the basolateral amygdala (BLA) have long been associated with abnormalities of taste-related behaviors and with failure in a variety of taste- and odor-related learning paradigms, including taste-potentiated odor aversion, conditioned taste preference, and conditioned taste aversion. Still, the general role of the amygdala in chemosensory learning remains somewhat controversial. In particular, it has been suggested that the amygdala may not be involved in a form of chemosensory learning that has recently received a substantial amount of study-socially transmitted food preference (STFP). Here, we provide evidence for this involvement by pharmacologically inactivating the basolateral amygdala bilaterally during STFP training. The same inactivation sites that impaired taste aversion learning eliminated the normally conditioned preference for a food smelled on a conspecific's breath. Impairments of learned preference persisted even in testing sessions in which BLA was not inactivated, and learning was normal when the BLA was inactivated only during testing sessions; thus, the impairment was a true acquisition deficit. In conjunction with previous results from other paradigms, therefore, our data suggest that the amygdala is vital for learning procedures involving pairings of potent and arbitrary chemosensory stimuli.

Amygdala↗