Biomedical subjects

Mikiko Kadohisa

Publications and source records attributed to Mikiko Kadohisa.

8 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

Separate encoding of identity and similarity of complex familiar odors in piriform cortex.

Piriform cortical circuits are hypothesized to form perceptions from responses to specific odorant features, but the anterior piriform cortex (aPCX) and posterior piriform cortex (pPCX) differ markedly in their anatomical organization, differences that could lead to distinct roles in odor encoding. Here, we tested whether experience with a complex odorant mixture would modify encoding of the mixture and its components in aPCX and pPCX. Rats were exposed to an odorant mixture and its components in a go/no-go rewarded odor discrimination task. After reaching behavioral performance criterion, single-unit recordings were made from the aPCX and pPCX in these rats and in odor-naïve, control, urethane-anesthetized rats. After odor experience, aPCX neurons were more narrowly tuned to the test odorants, and there was a decorrelation in aPCX population responses to the mixture and its components, suggesting a more distinct encoding of the familiar mixture from its components. In contrast, pPCX neurons were more broadly tuned to the familiar odorants, and pPCX population responses to the mixture and its components became more highly correlated, suggesting a pPCX encoding of similarity between familiar stimuli. The results suggest aPCX and pPCX play different roles in the processing of familiar odors and are consistent with an experience-dependent encoding (perceptual learning) of synthetic odorant identity in aPCX and an experience-dependent encoding of odor similarity or odor quality in pPCX.

Animals↗

PubMed2006

Cortical contributions to olfaction: plasticity and perception.

In most sensory systems, the sensory cortex is the place where sensation approaches perception. As described in this review, olfaction is no different. The olfactory system includes both primary and higher order cortical regions. These cortical structures perform computations that take highly analytical afferent input and synthesize it into configural odor objects. Cortical plasticity plays an important role in this synthesis and may underlie olfactory perceptual learning. Olfactory cortex is also involved in odor memory and association of odors with multimodal input and contexts. Finally, the olfactory cortex serves as an important sensory gate, modulating information throughput based on recent experience and behavioral state.

Animals↗

PubMed2005

Olfactory cortical adaptation facilitates detection of odors against background.

Detection and discrimination of odors generally, if not always, occurs against an odorous background. On any given inhalation, olfactory receptor neurons will be activated by features of both the target odorant and features of background stimuli. To identify a target odorant against a background therefore, the olfactory system must be capable of grouping a subset of features into an odor object distinct from the background. Our previous work has suggested that rapid homosynaptic depression of afferents to the anterior piriform cortex (aPCX) contributes to both cortical odor adaptation to prolonged stimulation and habituation of simple odor-evoked behaviors. We hypothesize here that this process may also contribute to figure-ground separation of a target odorant from background stimulation. Single-unit recordings were made from both mitral/tufted cells and aPCX neurons in urethan-anesthetized rats and mice. Single-unit responses to odorant stimuli and their binary mixtures were determined. One of the odorants was randomly selected as the background and presented for 50 s. Forty seconds after the onset of the background stimulus, the second target odorant was presented, producing a binary mixture. The results suggest that mitral/tufted cells continue to respond to the background odorant and, when the target odorant is presented, had response magnitudes similar to that evoked by the binary mixture. In contrast, aPCX neurons filter out the background stimulus while maintaining responses to the target stimulus. Thus the aPCX acts as a filter driven most strongly by changing stimuli, providing a potential mechanism for olfactory figure-ground separation and selective reading of olfactory bulb output.

Adaptation, Physiological↗

PubMed2005

Neuronal representations of stimuli in the mouth: the primate insular taste cortex, orbitofrontal cortex and amygdala.

The responses of 3687 neurons in the macaque primary taste cortex in the insula/frontal operculum, orbitofrontal cortex (OFC) and amygdala to oral sensory stimuli reveals principles of representation in these areas. Information about the taste, texture of what is in the mouth (viscosity, fat texture and grittiness, which reflect somatosensory inputs), temperature and capsaicin is represented in all three areas. In the primary taste cortex, taste and viscosity are more likely to activate different neurons, with more convergence onto single neurons particularly in the OFC and amygdala. The different responses of different OFC neurons to different combinations of these oral sensory stimuli potentially provides a basis for different behavioral responses. Consistently, the mean correlations between the representations of the different stimuli provided by the population of OFC neurons were lower (0.71) than for the insula (0.81) and amygdala (0.89). Further, the encoding was more sparse in the OFC (0.67) than in the insula (0.74) and amygdala (0.79). The insular neurons did not respond to olfactory and visual stimuli, with convergence occurring in the OFC and amygdala. Human psychophysics showed that the sensory spaces revealed by multidimensional scaling were similar to those provided by the neurons.

Adult↗

PubMed2004

Primate insular/opercular taste cortex: neuronal representations of the viscosity, fat texture, grittiness, temperature, and taste of foods.

It is shown that the primate primary taste cortex represents not only taste but also information about many nontaste properties of oral stimuli. Of 1,122 macaque anterior insular/frontal opercular neurons recorded, 62 (5.5%) responded to oral stimuli. Of the orally responsive neurons, some (53%) represented the viscosity, tested using carboxymethyl-cellulose in the range 1-10,000 cP. Other neurons (8%) responded to fat in the mouth by encoding its texture (as shown similar responses to nonfat oils), and 8% responded to gritty texture. Some neurons (35%) responded to the temperature of the liquid in the mouth. Some neurons responded to capsaicin, and others to fatty acids. Some neurons (56%) had taste responses. Some (50%) of these neurons were unimodal, responding to one of these types of stimulus, and the majority combined responsiveness to these types of stimulus, with 23% responding for example to both taste and temperature. Some neurons respond to taste, texture, and temperature unimodally, but others combine these inputs. None of these orally responsive neurons responded to odor or to the sight of food. These results provide fundamental evidence about the information channels used to represent the taste, texture, and temperature of food in the first cortical area involved in taste in the primate brain. The results are relevant to understanding the physiological and pathophysiological processes related to how the properties of oral stimuli are represented in the brain and thus to the control of food intake and food selection.

Action Potentials↗

PubMed2003

Representations of the texture of food in the primate orbitofrontal cortex: neurons responding to viscosity, grittiness, and capsaicin.

The primate orbitofrontal cortex (OFC) is a site of convergence from taste, olfactory, and somatosensory cortical areas. We describe a population of single neurons in the macaque OFC that responds to the texture of food in the mouth. Use of oral viscosity stimuli consisting of carboxymethylcellulose (CMC) in the range 1-10,000 centipoise showed that the responses of one subset of these neurons were related to stimulus viscosity. Some of the neurons had increasing responses to increasing viscosity, some had decreasing responses, and some neurons were tuned to a range of viscosities. These neurons are a different population to oral fat-sensitive neurons, in that their responses to fats (e.g., safflower oil), to silicone oil [(Si(CH3)2O)n], and to mineral oil (hydrocarbon) depended on the viscosity of these oils. Thus there is a dissociation between texture channels used to sense viscosity and fat. Some of these viscosity-sensitive single neurons were unimodal (somatosensory; 25%) and some received convergent taste inputs (75%). A second subpopulation of neurons responded to gritty texture (produced by microspheres suspended in CMC). A third subpopulation of neurons responded to capsaicin. These results provide evidence about the information channels used to represent the texture and flavor of food in a part of the brain important in appetitive responses to food and are relevant to understanding the physiological and pathophysiological processes related to food intake, food selection, and the effects of variety of food texture in combination with taste and other inputs that affect food intake.

Algorithms↗

PubMed2003

Neurons in the primate orbitofrontal cortex respond to fat texture independently of viscosity.

The primate orbitofrontal cortex (OFC) is a site of convergence from primary taste, olfactory, and somatosensory cortical areas. We describe the responses of a population of single neurons in the OFC that respond to orally applied fat (e.g., safflower oil) and to substances with a similar texture but different chemical composition, such as mineral oil (hydrocarbon) and silicone oil [(Si(CH3)2O)n]. These findings provide evidence that the neurons respond to the oral texture of fat, sensed by the somatosensory system. Use of an oral viscosity stimulus consisting of carboxymethyl-cellulose in the range 1-10,000 centipoise (cP) showed that the responses of these fat-sensitive neurons are not related to stimulus viscosity. Thus a textural component independent of viscosity and related to the slick or oily property is being used to activate these oral fat-sensitive neurons. Moreover, a separate population of neurons responds to viscosity (produced, e.g., by the carboxymethyl-cellulose series), but not to fat with the same viscosity. Thus there is a dissociation between texture channels used to sense fat viscosity and non-fat-produced viscosity. Further, free fatty acids such as linoleic acid do not activate these neurons, providing further evidence that the oral fat-sensing mechanism through which these OFC neurons are activated is not gustatory but textural. Most of this population of fat-sensitive neurons receive convergent taste inputs. These results provide evidence about how oral fat is sensed and are relevant to understanding the physiological and pathophysiological processes related to fat intake.

Action Potentials↗