Responsiveness to olfactory stimuli presented in sleep

Whether humans react to olfactory stimuli presented in sleep was assessed. Responses of ten participants (mean age = 22.8 years) were recorded to repeated three-minute periods of either air alone or to a peppermint odor (0.26 mg/liter) during stage 2 sleep. These responses included behavioral (awakening, microswitch closure), autonomic (heart rate, EMG, respiration), and central (EEG) components. An odor delivery system is described comprised of an aquarium pump, Teflon and TYGON tubing, oxygen mask, filtering, and air flow valves. The data indicate that humans react behaviorally, autonomically and centrally to olfactory stimuli presented while sleeping. Although the percentage of overall responsivity to olfactory stimuli was low, significant differences (ANOVA) in responsivity to odor periods vs. nonodor periods were found for microswitch closures, EEG, EMG, and heart rate. For these measures eight or more of the ten participants showed this pattern of differential responsivity during odor and nonodor periods (Sign test = p less than 0.05). A time-of-night effect was also observed in that responsivity tended to be greatest early in the night. The effect on responsivity of other durations, concentrations, and odors requires additional research.     

Respiratory responses associated with affective processing of film stimuli

We investigated respiratory responses during film clip viewing and their relation to the affective dimensions of valence and arousal. Seventy-six subjects participated in a study using a between groups design. To begin with, all participants viewed an emotionally neutral film clip. Then, they were presented with one out of four emotional film clips: a positive high-arousal, a positive low-arousal, a negative high-arousal and a negative low-arousal clip. Respiration, skin conductance level, heart rate, corrugator activity and affective judgments were measured. Expiratory time was shorter and inspiratory duty cycle, mean expiratory flow and minute ventilation were larger during the high-arousal clips compared to the low-arousal clips. The pleasantness of the stimuli had no influence on any respiratory measure. These findings confirm the importance of arousal in respiratory responding but also evidence differences in comparison to previous studies using visual and auditory stimuli.     

Postural muscle responses to multidirectional translations in patients with Parkinson's disease

The postural adaptation impairments of patients with Parkinson's disease (PD) suggest that the basal ganglia may be important for quickly modifying muscle activation patterns when the direction of perturbation or stance conditions suddenly change. It is unknown whether their particular instability to backward postural perturbations is due to specific abnormalities of parkinsonian postural muscle synergies in that direction and not present in other directions. In the present study, we test this hypothesis by comparing the patterns of leg and trunk muscle activation in 13 subjects with PD and 13 control subjects in response to eight randomly presented directions of horizontal surface translations while standing with either narrow or wide stance. The direction of maximum activation for each muscle was similar for PD and control subjects, suggesting that the basal ganglia is not critical for programming externally triggered postural synergies. However, antagonist muscle activation was earlier and larger in PD than in control subjects, resulting in coactivation. PD subjects also did not increase the magnitude of muscle activation as much as did control subjects when changing from wide to narrow stance. These results are consistent with the hypothesis that PD results in an inability to shape the pattern and magnitude of postural muscle responses for changes in perturbation direction and in stance position.     

Microglial responses to dopamine in a cell culture model of Parkinson's disease

Activated microglia appear to selectively attack dopamine (DA) neurons in the Parkinson's disease (PD) substantia nigra. We investigated potential mechanisms using culture models. As targets, human SH-SY5Y cells were left undifferentiated (UNDIFF) or were differentiated with retinoic acid (RA) or RA plus brain-derived neurotrophic factor (RA/BDNF). RA/BDNF-treated cells were immunoreactive for tyrosine hydroxylase and the DA transporter, took up exogenous DA, and released DA after K(+) stimulation. Undifferentiated and RA-treated cells lacked these characteristics of a DA phenotype. Co-culture of target cells with human elderly microglia resulted in elevated toxicity in DA phenotype (RA/BDNF) cells. Lipopolysaccharide (LPS) plus K(+)-stimulated DA release enhanced toxicity by 500-fold. DA induced microglial chemotaxis in Boyden chambers. Spiperone inhibited this effect. Cultured human elderly microglia expressed mRNAs for D1-D4 but not D5 DA receptors. The microglia, as well as PD microglia in situ, were also immunoreactive for D1-D4 but not D5 DA receptors. These findings demonstrate that activated microglia express DA receptors, and suggest that this mechanism may play a role in the selective vulnerability of DA neurons in PD.     

Reliability analysis of event-related brain potentials to olfactory stimuli

Olfactory event-related potentials (OERP) have been used to investigate olfactory processing in health and disease. However, the reliability of the OERP has yet to be established statistically. The present study examined test-retest reliability of the OERP over a 4-week interval. EEG was recorded from Fz, Cz, and Pz, using a single-stimulus paradigm with amyl acetate. Reliabilities for ERP component latencies and interpeak amplitudes were assessed as intraclass and Pearson product-moment correlation coefficients. Reliabilities were higher for latency than for amplitude. Highest correlation coefficients were observed for P2 latency, specifically at Cz and Pz P3 amplitude and latency exhibited high reliability at Cz and Pz. Fz demonstrated weakest correlation coefficients. The data suggest that OERP reliability is comparable to that of auditory and visual ERPs, supporting the use of OERPs in both basic research and clinical assessment.     

Defensive responses to phobic stimuli.

Physiological recordings were made while nine females who were afraid of spiders (group P) and nine who were not (group N) viewed a random series of spider and neutral slides. Group P's responses to the spider slides included heart rate (HR) acceleration, cephalic vasoconstriction and an increase in palmer skin conductance (SC), a pattern considered to be part of a defensive response (DR). Group N's responses, on the other hand, were indicative of an orienting response (OR), and included HR deceleration, cephalic vasodilation and an increase in palmar SC. The neutral slides elicited little in the way of responses from group N. However, they elicited the cardiovascular and electrodermal components of an OR from group P, presumably because of their contrast with the feared spider slides. Although the DR pattern observed in group P was often accompanied by increased somatic activity, HR acceleration and cephalic vasoconstriction still occurred even when somatic activity did not appear to increase.     

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.     

Day-night difference in thermoregulatory responses to olfactory stimulation

Previously, we observed that olfactory stimulation with scent of grapefruit oil (SGFO) or scent of lavender oil (SLVO) affected, elevated or lowered brown adipose tissue temperature (BAT-T) in conscious mice, respectively. In the present study, to test the day-night difference in the actions of olfactory stimulations, we examined the responses of BAT-T and body temperature (BT) measured as the abdominal temperature to SGFO or SLVO during day-time at 14:00 and night-time at 2:00 in conscious rats. In the light period, BAT-T and BT were suppressed after SLVO and elevated after SGFO whereas in the dark period, these parameters remained unchanged with olfactory stimulations. Bilateral lesions of the hypothalamic suprachiasmatic nucleus (SCN) eliminated the effects of olfactory stimulations with SGFO and SVLO on BAT-T and BT. Moreover, sympathetic nerve activity innervating brown adipose tissue (BAT-SNA) changes after SGFO or SLVO were abolished in SCN-lesioned rats. Thus, we concluded that there is day-night difference in the effects of SGFO or SLVO on BAT-T and BT, and that the SCN might be involved in these effects.     

Competitive dynamics in cortical responses to visual stimuli

Neurons in the visual cortex of the macaque monkey exhibit a variety of competitive behaviors, including normalization and oscillation, when presented with multiple visual stimuli. Here we argue that a biophysically plausible cortical circuit with opponent inhibition, spike-frequency adaptation, and synaptic depression can account for the full range of behaviors. The governing parameter is the strength of inhibition between competing neuronal pools. As the strength of inhibition is increased, the pattern of network behavior shifts from normalization mode to oscillatory mode, with oscillations occurring at progressively lower frequency until, at the extreme, winner-take-all behavior appears.     

Respiratory responses to changes in air density

Summary The use of a 4 to 1 mixture of helium and oxygen in maximal work does not increase the capacity for transporting oxygen nor greatly modify the heart rate. It does favor the elimination of carbon dioxide. It is associated with the same increase in lactic acid but at the same time it favors the elimination of carbon dioxide; accordingly the change in p_H is smaller.     

Habenular lesions and discrimination responding to olfactory and visual stimuli

Twenty albino rats with either bilateral habenular lesions or sham operations were trained to discriminate on the basis of olfactory cues between two compartments of a Grice apparatus modified for odor presentation. The discriminative stimulus consisted of different relative concentrations of the odor substance Lilial ranging from 0.1% to 10% air-diluted concentrations. The animals were initially trained using a 10% relative odor stimulus and subsequently tested with a descending series of odorant concentrations. All animals except one acquired the initial discrimination, but successive lowering of the odor concentration disrupted the performance of the experimental group while all controls successfully reached criterion at the lowest concentration used. The rat failing to make the initial odor discrimination was able to discriminate between the two compartments when a visual cue was substituted for the olfactory stimulus. We conclude that the habenular area serves as an important link between olfactory sensory input and motor systems in the rat. It appears that the behavioral changes observed are related more to threshold elevation or an impairment in olfactory integration than to generalized disruption of response inhibition mechanisms.     

Expectation enhances event-related responses to affective stimuli

How the expectation of forthcoming emotional events influences individuals’ behaviors and brain responses to such events remains controversial. The present study addressed this issue using event-related potentials (ERPs) to overcome limitations in research techniques. In addition, a no cue condition was adopted as the unexpected condition to make the research paradigm closer to real life situations for ecological validity. Behavioral results showed that positive stimuli were experienced more pleasantly and negative ones were experienced more unpleasantly during the expected condition than the unexpected one. ERPs results also displayed larger P2, N2 and LPP amplitudes in the expected condition, regardless of stimulus valence. The finding that expected emotional events evoke enhanced behavioral and brain responses than the unexpected ones do provides a strong piece of evidence for the effect of expectation on emotion processing.     

Event-related potential responses to love-related facial stimuli

In event-related potential (ERPs) studies, emotional stimuli usually elicit an enhanced late positive potential (LPP), which is assumed to reflect motivated attention. However, whether a stimulus elicits emotional responses may depend on the individual's state, such as experiencing romantic love. It has been suggested that stimuli that are related to someone's beloved will elicit increased attention in that infatuated individual. In this study, participants who were in love viewed faces of their beloved, their friend, and of an unknown, beautiful person. The friend was included to control for familiarity, and the unknown person for perceived beauty. As expected, the LPP was larger in response to the face of the beloved than to the other two emotionally significant faces. Interpreting the LPP as reflecting motivated attention, this implies that romantic love is accompanied by increased attention for the face of one's beloved.     

Foveal attention modulates responses to peripheral stimuli

When attending to a visual object, peripheral stimuli must be monitored for appropriate redirection of attention and gaze. Earlier work has revealed precentral and posterior parietal activation when attention has been directed to peripheral vision. We wanted to find out whether similar cortical areas are active when stimuli are presented in nonattended regions of the visual field. The timing and distribution of neuromagnetic responses to a peripheral luminance stimulus were studied in human subjects with and without attention to fixation. Cortical current distribution was analyzed with a minimum L1-norm estimate. Attention enhanced responses 100-160 ms after the stimulus onset in the right precentral cortex, close to the known location of the right frontal eye field. In subjects whose right precentral region was not distinctly active before 160 ms, focused attention commonly enhanced right inferior parietal responses between 180 and 240 ms, whereas in the subjects with clear earlier precentral response no parietal enhancement was detected. In control studies both attended and nonattended stimuli in the peripheral visual field evoked the right precentral response, whereas during auditory attention the visual stimuli failed to evoke such response. These results show that during focused visual attention the right precentral cortex is sensitive to stimuli in all parts of the visual field. A rapid response suggests bypassing of elaborate analysis of stimulus features, possibly to encode target location for a saccade or redirection of attention. In addition, load for frontal and parietal nodi of the attentional network seem to vary between individuals.     

Cortical responses to noxious stimuli during sleep

We used magnetoencephalography to study effects of sleep on cortical responses to noxious stimuli and to clarify the mechanisms underlying pain perception. For a noxious stimulus, painful intra-epidermal electrical stimulation, which selectively activates A-delta fibers, was applied to the dorsum of the left hand. While awake, subjects were asked to count the number of stimuli silently (Attention) or ignore the stimuli (Control). During sleep, magnetic fields recorded in stage 1 sleep and stage 2 sleep were analyzed. One main component at a latency around 140-160 ms was identified in the awake condition. Multiple source analysis indicated that this main component was generated by activities in the contralateral primary somatosensory cortex (SI), bilateral secondary somatosensory cortex (SII) and insular cortex. The medial temporal area (MT) and cingulate cortex were activated later than the main component. Cortical responses in the contralateral SI, ipsilateral SII and MT, bilateral insula and cingulate cortex were significantly enhanced in Attention as compared with Control. The main component 1 M as well as later magnetic fields were markedly attenuated during sleep, suggesting that all these cortical areas are involved in pain cognition.     

Expectation enhances event-related responses to affective stimuli

Extensive practice is associated with a higher level of learning than practice until performance stabilization. This is partially attributable to the changes in the variability of the structure that control the motor skill that occur during practice. However, because both conditions result in performance stabilization, the error in the task performance does not decrease further, and it is necessary to introduce higher demands (e.g., unpredictable perturbations) into the task for differences between the two conditions to arise. This study aimed to investigate whether extensive practice contributes to adaptation to unpredictable perturbations in a sequential motor skill task as compared to practice until performance stabilization. Thirty-four self-reported right handed young adults performed a sequential coincident timing task and were assigned to two groups during the first phase of experiment: the stabilization group (SG) or the extensive practice group (EG), which differs with respect to the quantity of practice. In the second phase, both groups performed under equal conditions and the subjects practiced the same task performed in the first phase, but unpredictable changes in the velocity of the visual stimulus were occasionally introduced. The results suggest that extensive practice improves adaptation to unpredictable perturbations better than practice until performance stabilization and indicates that the motor learning process continues after performance stabilization.     

Abnormal proprioceptive-motor integration contributes to hypometric postural responses of subjects with Parkinson's disease

Subjects with Parkinson's disease exhibit abnormally short compensatory steps in response to external postural perturbations. We examined whether: (1) Parkinson's disease subjects exhibit short compensatory steps due to abnormal central proprioceptive-motor integration, (2) this proprioceptive-motor deficit can be overcome by visual-motor neural circuits using visual targets, (3) the proprioceptive-motor deficit relates to the severity of Parkinson's disease, and (4) the dysfunction of central dopaminergic circuits contributes to the Parkinson's disease subjects' proprioceptive-motor deficit. Ten Parkinson's disease subjects and 10 matched control subjects performed compensatory steps in response to backward surface translations in five conditions: with eyes closed, with eyes open, to a remembered visual target, to a target without seeing their legs, and to a target while seeing their legs. Parkinson's disease subjects were separated into a moderate group and a severe group based on scores from the Unified Parkinson's Disease Rating Scale and were tested off and on their dopamine medication. Parkinson's disease subjects exhibited shorter compensatory steps than did the control subjects, but all subjects increased their step length when stepping to targets. Compared with the other subject groups, the severe Parkinson's disease subjects made larger accuracy errors when stepping to targets, and the severe Parkinson's disease subjects' step accuracy worsened the most when they were unable to see their legs. Thus, Parkinson's disease subjects exhibited short compensatory steps due to abnormal proprioceptive-motor integration and used visual input to take longer compensatory steps when a target was provided. In severe Parkinson's disease subjects, however, visual input does not fully compensate because, even with a target and unobstructed vision, they still exhibited poor step accuracy. Medication did not consistently improve the length and accuracy of the Parkinson's disease subjects' compensatory steps, suggesting that degeneration of dopamine circuits within the basal ganglia is not responsible for the proprioceptive-motor deficit that degrades compensatory steps in Parkinson's disease subjects.