Biomedical subjects

H D Critchley

Publications and source records attributed to H D Critchley.

22 records · Page 2Linked to original sources

PubMed1996

Hunger and satiety modify the responses of olfactory and visual neurons in the primate orbitofrontal cortex.

1. The primate orbitofrontal cortex is the site of convergence of information from primary taste and primary olfactory cortical regions. In addition, it receives projections from temporal lobe visual areas concerned with the representation of objects such as foods. Previous work has shown that the responses of gustatory neurons in the secondary taste area within the orbitofrontal cortex are modulated by hunger and satiety, in that they stop responding to the taste of a food on which an animal has been fed to behavioral satiation, yet may continue to respond to the taste of other foods. 2. This study demonstrates a similar modulation of the responses of olfactory and visual orbitofrontal cortex neurons after feeding to satiety. Seven of nine olfactory neurons that were responsive to the odors of foods, such as blackcurrant juice, were found to decrease their responses to the odor of the satiating food in a selective and statistically significant manner. 3. It also was found for eight of nine neurons that had selective responses to the sight of food, that they demonstrated a sensory-specific reduction in their visual responses to foods after satiation. 4. The responses of orbitofrontal cortex neurons selective for foods in more than one modality also were analyzed before and after feeding to satiation. Satiety often affected the responses of these multimodal neurons across all modalities, but a sensory-specific effect was not always demonstrable for both modalities. 5. These findings show that the olfactory and visual representations of food, as well as the taste representation of food, in the primate orbitofrontal cortex are modulated by hunger. Usually a component related to sensory-specific satiety can be demonstrated. The findings link at least part of the processing of olfactory and visual information in this brain region to the control of feeding-related behavior.

Analysis of Variance↗

PubMed1996

Orbitofrontal cortex neurons: role in olfactory and visual association learning.

1. The orbitofrontal cortex is implicated in the rapid learning of new associations between visual stimuli and primary reinforcers such as taste. It is also the site of convergence of information from olfactory, gustatory, and visual modalities. To investigate the neuronal mechanisms underlying the formation of odor-taste associations, we made recordings from olfactory neurons in the orbitofrontal cortex during the performance of an olfactory discrimination task and its reversal in macaques. 2. It was found that 68% of odor-responsive neurons modified their responses after the changes in the taste reward associations of the odorants. Full reversal of the neuronal responses was seen in 25% of these neurons. Extinction of the differential neuronal responses after task reversal was seen in 43% of these neurons. 3. For comparison, visually responsive orbitofrontal neurons were tested during reversal of a visual discrimination task. Seventy-one percent of these visual cells showed rapid full reversal of the visual stimulus to which they responded, when the association of the visual with taste was reversed in the reversal task. 4. These demonstrate that of many orbitofrontal cortex olfactory neurons on the taste with which the odor is associated. 5. This modification is likely to be important for setting the motivational value of olfactory for feeding and other rewarded behavior. However, it is less complete, and much slower, than the modifications found or orbit frontal visual during visual-taste reversal. This relative inflexibility of olfactory responses is consistent with the need for some stability is odor-taste associations to facilitate the formation and perception of flavors.

Acoustic Stimulation↗

PubMed1996

Representation of olfactory information in the primate orbitofrontal cortex.

1. To analyze the information represented about individual odor stimuli in the responses of single olfactory neurons in the primate orbitofrontal area, neuronal responses were measured to a set of seven to nine odorants in macaques performing an olfactory discrimination task. The population of neurons analyzed had responses that were significantly differential to the odorants. 2. Information theoretic analyses were applied to the responses of the neurons, and information measures were calculated from the firing rate of the responses and from the principal components of the responses. The information reflected by the firing rate of the response accounted for the majority of the information present (86%) when compared with the information derived from the first three principal components of the spike train. This indicated that temporal encoding had a very minor role in the encoding of olfactory information by single orbitofrontal olfactory cells. 3. The average information about which odorant was presented, averaged across the 38 neurons, was 0.09 bits, a figure that is low when compared with the information values previously published for the responses of temporal lobe face-selective neurons. 4. Application of information theoretic analyses to the responses of these neurons showed how much information about which stimulus was delivered was present in the responses of individual neurons. It was found that for the majority of the neurons significant amounts of information were reflected about one or two of the odorants presented. 5. For each neuron, the information reflected in the responses of that neuron about the reinforcement value and the information about the identity of the odorants were calculated. It is shown that many neurons carry information about which of the odorants was presented; in addition, some neurons reflect information only about the taste association of the stimuli and not about odorant identity. 6. Measurements of the sparseness of the representation indicated that a broadly distributed representation of the identity of odorants was present in this population of neurons.

Animals↗

PubMedDate not supplied

Responses of neurons in the primate taste cortex to the glutamate ion and to inosine 5'-monophosphate.

To investigate the neural encoding of glutamate taste in the primate, recordings were made from taste responsive neurons in the cortical taste areas in macaques. Most of the neurons were in the orbitofrontal cortex taste area, with a small number in adjacent taste areas. First, it was shown that single neurons that had their best responses to sodium glutamate also had good responses to glutamic acid. The correlation between the responses to these two tastants was higher than between any other pair of tastants, which included glucose (sweet), sodium chloride (salty), HCl (sour), and quinine HCl (bitter). Accordingly, the responsiveness to glutamic acid clustered with the response to monosodium glutamate in a cluster analysis with this set of stimuli, and glutamic acid was close to sodium glutamate in a space created by multidimensional scaling. Second, it was shown that the responses of these neurons to the nucleotide umami tastant inosine 5'-monophosphate were more correlated with their responses to monosodium glutamate than to any prototypical tastant. Third, concentration response curves showed that concentrations of monosodium glutamate as low as 0.001 M were just above threshold for some of these neurons. Fourth, neurons have not yet been found in this cortical region that showed synergism of monosodium glutamate and the nucleotide inosine 5'-monophosphate: it was shown that mixtures of 0.0001 M inosine 5'-monophosphate with different concentrations (0.001, 0.01, and 0.1 M) of monosodium glutamate did not have a greater effect than the monosodium glutamate alone. Fifth, some neurons in the orbitofrontal region, which responded to monosodium glutamate and other food tastes, decreased their responses after feeding with monosodium glutamate to behavioural satiety. In some cases this reduction was sensory-specific. These findings show that the taste neurons activated by monosodium glutamate can also be activated by other umami tastants, including glutamic acid and the nucleotide inosine 5'-monophosphate. The responses to these umami tastants were more similar to each other than to any of the other prototypical tastants, providing evidence that in this system umami is encoded differently from the other tastants. Moreover, the findings with these tastants provide additional evidence that the responses to monosodium glutamate are not due just to activation of a sodium taste channel.

Animals↗