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At least 127 records · Page 7Linked to original sources
PubMed2000

Sex differences in the perception of tactile simultaneity.

A tactile simultaneity task was used to investigate the effects of sex on simultaneity thresholds. Participants were required to judge whether pairs of tactile stimuli delivered unimanually or bimanually were simultaneous. Unimanual stimulation delivered stimuli to the same cerebral hemisphere, while bimanual stimulation resulted in the delivery of one stimulus to each hemisphere, therefore requiring interhemispheric transmission before judging simultaneity. The data of 114 right-handed participants were analysed. Females (N = 56) perceived simultaneity at longer intervals than males (N = 58) when bimanual stimulation was received. Furthermore, males had shorter interhemispheric transmission times (10.9 ms) than those of females (15.0 ms). The results also provided some support for the predictions of the Hemispheric Equivalence Model of temporal processing since bimanual simultaneity thresholds were longer than unimanual; and unimanual stimulation of the left vs right hand did not differ. An advantage for stimulation of right hand first (vs left first) in the bimanual condition was small (2.7 ms), and was the only prediction of the Left Hemisphere Specialisation Model to receive support. A modification of the Equivalence Model which allows for a slight left hemispheric advantage is proposed.

Adolescent↗
PubMed2003

Differences between tooth stimulation and capsaicin-induced neurogenic vasodilatation in human gingiva.

Animal experiments have shown that the application of capsaicin to oral mucosa leads to a neurogenic inflammation associated with blood flow elevations in gingivomucosal tissues. In this investigation, we measured the tooth stimulation and capsaicin-evoked blood flow responses in maxillary gingiva in humans to study whether axon-reflex-mediated vasodilatation crosses the midline of the maxilla. The vasoactive reactions were mapped by laser Doppler imaging. Unilateral stimulation of alveolar mucosa and attached gingiva by capsaicin evoked a distinct neurogenic vasodilatation in ipsilateral gingiva, which rapidly attenuated at the midline. Capsaicin stimulation of alveolar mucosa provoked clear inflammatory reactions. In contrast to capsaicin stimuli, tooth stimulation produced symmetrical vasodilatations bilaterally in the gingiva. The ipsilateral responses were significantly smaller during tooth stimulation than during capsaicin stimuli. Analysis of these data suggests that capsaicin-induced inflammatory reactions in gingivomucosal tissues do not cross the midline in the anterior maxilla. The enhanced reaction found during stimulation of alveolar mucosa indicates that alveolar mucosa is more sensitive to chemical irritants than attached gingiva.

Adult↗
PubMed1975

[Electroretinographic study on the causal relationship of the S-R effect].

In the continuation of earlier studies, further serial-stimulation experiments with prolonged duration of single stimuli were carried out on dark-adapted frogs. The results have revealed a far-going dependence of the retinal response patterns (S-R effect) on the time relations between single stimuli and stimulation intervals. From all the experimental evidence available to date it can be concluded that the demonstrated serial-stimulation effects are brought about primarily in the photorecptors. According to reports in the literature these receptors in the state of dark adaptation respond to intensive, overriding stimuli with a pronounced after-effect causing a reduction of the temporal resolution capacity and of the difference susceptibility. The suppression effect can be regarded as a consequence of this overriding reaction. On the other hand, the recovery effect is caused most probably by the suddenly occurring bright adaptation because the latter makes the after-effect disappear quickly.

Animals↗
PubMed2006

Masking visual stimuli by transcranial magnetic stimulation.

Transcranial magnetic stimulation (TMS) applied over the occipital pole can suppress visual perception. Since its first description in 1989 by Amassian et al., this technique has widely been used to investigate visual processing at the cortical level. This article presents a review of experiments masking visual stimuli by TMS. The psychophysical characterization of TMS masking, the dependence on stimulus onset asynchrony between visual stimulus and TMS pulse, and the topography of masking within the visual field are considered. The relation between visual masking and the generation of phosphenes is discussed as well as the underlying physiological mechanisms.

Evoked Potentials, Visual↗
PubMed1994

Long latency transient evoked potentials to rapid random stimulation: responses to single and multiple concurrent stimuli.

In EP testing, regular (periodic) stimulation at increasing rates produces progressive fusion of responses into steady-state wave forms. When stimuli are presented randomly in time this fusion does not occur. Medium and long latency transient EPs can be recorded to stimulation at interstimulus intervals which are much shorter than the EP wave form latencies. Individual transient EPs can be obtained to multiple independent stimuli presented concurrently when the stimuli are presented randomly to one another. The ability to obtain responses to rapid stimulation and to multiple independent stimuli provides opportunities for increased efficiency and complexity of testing, particularly involving long latency responses.

Acoustic Stimulation↗
PubMed2002

Cortical representation of venous nociception in humans.

Painful sensations can be evoked by application of thermal, mechanical, and chemical stimuli to the blood vessels. The cortical substrates of these sensations are unknown. We therefore used whole-head magnetoencephalography to record cortical responses to painful laser stimuli applied cutaneously and intravenously to the dorsum of the hand in healthy human subjects. Similar to the cutaneous stimuli, venous stimulation nearly simultaneously activated the contralateral primary and the bilateral secondary somatosensory cortices. In the venous stimulation condition, all activation peaks were about 50 ms earlier than in the cutaneous stimulation condition. Locations of responses to both stimuli did not differ. These results show that the afferent volley from the veins reaches the cerebral cortex significantly earlier than that from the skin. This might be due to differences in peripheral conduction velocity. Apart from this, these findings demonstrate that venous nociception shares the cortical representation of cutaneous nociception in human somatosensory cortices. Thus the cortical representation of nociceptive processing from tissues of mesodermal and ectodermal origin appears to be similar.

Adult↗
PubMed1989

Effects of intraoral mechanoreceptor stimulation on reticular formation neurones, in the rabbit.

The effects of intraoral mechanoreceptor stimulation on the firing rate of single neurones of the brain stem reticular formation (RF) were investigated in rabbits. 30% of RF neurones responded to periodontal mechanoreceptor stimulation; 16% to mucosal mechanoreceptor stimulation and 6% to both types of stimuli. Periodontal stimulation induced mainly inhibitory effects localized within the mesencephalic and rostral pontine RF. Among periodontal afferents incisors were the most widely represented. The effects of mucosal mechanoreceptor stimulation were predominant in the medullary and pontine RF and they were mainly excitatory. The present results support the hypothesis that brain stem RF neurones can be recruited into regulating mastication and biting also by stimulation of intraoral mechanoreceptors.

Action Potentials↗
PubMed1999

The role of nucleus accumbens dopamine in motivated behavior: a unifying interpretation with special reference to reward-seeking.

Studies addressing behavioral functions of dopamine (DA) in the nucleus accumbens septi (NAS) are reviewed. A role of NAS DA in reward has long been suggested. However, some investigators have questioned the role of NAS DA in rewarding effects because of its role in aversive contexts. As findings supporting the role of NAS DA in mediating aversively motivated behaviors accumulate, it is necessary to accommodate such data for understanding the role of NAS DA in behavior. The aim of the present paper is to provide a unifying interpretation that can account for the functions of NAS DA in a variety of behavioral contexts: (1) its role in appetitive behavioral arousal, (2) its role as a facilitator as well as an inducer of reward processes, and (3) its presently undefined role in aversive contexts. The present analysis suggests that NAS DA plays an important role in sensorimotor integrations that facilitate flexible approach responses. Flexible approach responses are contrasted with fixed instrumental approach responses (habits), which may involve the nigro-striatal DA system more than the meso-accumbens DA system. Functional properties of NAS DA transmission are considered in two stages: unconditioned behavioral invigoration effects and incentive learning effects. (1) When organisms are presented with salient stimuli (e.g., novel stimuli and incentive stimuli), NAS DA is released and invigorates flexible approach responses (invigoration effects). (2) When proximal exteroceptive receptors are stimulated by unconditioned stimuli, NAS DA is released and enables stimulus representations to acquire incentive properties within specific environmental context. It is important to make a distinction that NAS DA is a critical component for the conditional formation of incentive representations but not the retrieval of incentive stimuli or behavioral expressions based on over-learned incentive responses (i.e., habits). Nor is NAS DA essential for the cognitive perception of environmental stimuli. Therefore, even without normal NAS DA transmission, the habit response system still allows animals to perform instrumental responses given that the tasks take place in fixed environment. Such a role of NAS DA as an incentive-property constructor is not limited to appetitive contexts but also aversive contexts. This dual action of NAS DA in invigoration and incentive learning may explain the rewarding effects of NAS DA as well as other effects of NAS DA in a variety of contexts including avoidance and unconditioned/conditioned increases in open-field locomotor activity. Particularly, the present hypothesis offers the following interpretation for the finding that both conditioned and unconditioned aversive stimuli stimulate DA release in the NAS: NAS DA invigorates approach responses toward 'safety'. Moreover, NAS DA modulates incentive properties of the environment so that organisms emit approach responses toward 'safety' (i.e., avoidance responses) when animals later encounter similar environmental contexts. There may be no obligatory relationship between NAS DA release and positive subjective effects, even though these systems probably interact with other brain systems which can mediate such effects. The present conceptual framework may be valuable in understanding the dynamic interplay of NAS DA neurochemistry and behavior, both normal and pathophysiological.

Animals↗
PubMed1990

Conditioning as a critical determinant of sensitization induced by psychomotor stimulants.

It is apparent that stimuli associated with psychomotor stimulants as well as opiates acquire the ability to elicit motor behaviors that probably reflect the acquisition and operation of incentive motivational processes. Such conditioning also appears to be a critical determinant of behavioral sensitization seen with repetitive administration of these agents. The conditioning of motor excitation to stimuli associated with psychomotor stimulants follows the principles of classical conditioning and is relatively long lasting. Dopaminergic mechanisms appear to be involved in the acquisition of such conditioned behaviors, since neuroleptics are effective blockers of the process. Dopaminergic blockade probably disrupts conditioning through several different mechanisms including attenuation of the conditioned and unconditioned excitatory properties of the CS and blockade of the US. DA blockade prevents stimuli associated with psychomotor stimulants from acquiring and subsequently generating positive affective motivational states that are reflected by increases in motoric output. While dopamine appears to be necessary for the formation of conditioned motor excitation, it is not critically involved in the expression of the conditioned effects. This seems to suggest that DA may serve only to modulate the formation of motivationally significant associations but is not involved in the expression of conditioned drug effects that may be mediated through DA-independent pathways. The amygdala and nucleus accumbens are two structures in the CNS involved in the acquisition of conditioned motor excitation. Interestingly, both of these brain regions are the recipients of mesolimbic DA input. Dopamine probably plays different roles in each region during the conditioning process. In the amygdala, mesolimbic DA may serve to modulate processes that attach emotional significance to environmental stimuli; further, DA may play a role in determining which stimuli gain access to structures afferent to the amygdala, including the nucleus accumbens. Dopamine in the nucleus accumbens, on the other hand, serves to determine which limbic inputs gain access to the motor pathways. In this way, DA in the nucleus accumbens may translate the motivational determinants of behavior that are mediated by limbic structures into biologically relevant actions. Understanding the mechanisms that determine the conditioning of drug effects to associated stimuli also has possible relevance for elucidating processes underlying addictive behaviors. For example, it has been proposed (Stewart et al. 1984) that the acquisition of incentive motivational properties by stimuli associated with drugs determines the craving in addicts.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed2002

Inhibition of human muscle sympathetic activity by sensory stimulation.

Surprising sensory stimuli causing arousal are known to evoke short-lasting activation of human sympathetic activity in skin but not in muscle nerves; anecdotal observations suggest that there may even be an inhibition of muscle sympathetic nerve activity (MSNA). To test this hypothesis we recorded multiunit MSNA in the peroneal nerve in 19 subjects aged 19-71 years, while sensory stimuli, consisting of either an electrical skin stimulus to a finger or a visual flash, were delivered repeatedly with intervals of approximately 20 s. The stimuli were given either 200 or 400 ms after the R wave of the electrocardiogram. Dummy stimuli, consisting of trigger pulses without sensory stimulation served as controls. Electrical skin resistance reductions were monitored from the palm of a hand as electrodermal signs of arousal-induced cutaneous sympathetic activity. On a group basis both types of sensory stimuli attenuated the amplitude of one or two bursts of MSNA, while no such effects occurred after dummy stimuli. Individually, the inhibition was evoked by at least one stimulus modality or delay in 16 subjects whereas in three subjects no significant inhibition occurred. Skin resistance responses were evoked in all subjects. Some subjects responded to one, others to both stimulus modalities, and electrical stimuli were more effective than visual stimuli in causing MSNA inhibition as well as skin resistance reduction. On the other hand, electrodermal signs of arousal were equally common in subjects with and without inhibitory responses. We suggest that the MSNA inhibition evoked by sensory stimuli is an arousal effect which varies markedly between individuals.

Adult↗
PubMed1993

Sex differences in responsiveness to painful and non-painful stimuli are dependent upon the stimulation method.

Sex differences in thermo- and electrocutaneous responsiveness to painful and non-painful stimuli were investigated in 20 women and 20 men. Heat pain, warmth, and cold thresholds were assessed on the hand and foot with a Peltier thermode system. In addition, subjects used magnitude estimation to judge the sensation intensity evoked by temperatures ranging from 38 degrees C to 48 degrees C applied to the forearm. To measure detection, pain, and tolerance thresholds of electrocutaneous sensitivity, electrical pulses were administered to the hand. Magnitude estimates of sensation intensity were assessed for stimuli ranging from 0.5 mA to 4.0 mA. There were no sex differences in heat pain, warmth and cold thresholds. There were significant sex differences in electrical detection, pain and tolerance thresholds, with lower thresholds in women. Correspondingly, magnitude estimates were similar in women and men when using thermal stimuli while women judged stimuli from 2.5 mA on as more intense than men when using electrical stimuli. Despite these discrepancies, the measures for pain responsiveness from the two stimulation methods correlated significantly. In contrast, no significant correlations between the methods were found when considering the responsiveness to non-painful stimuli. The findings help to clarify controversies in the pain literature about sex differences. Results affirming and denying such differences could be obtained within a single sample, with stimulation method as the critical variable.

Adult↗
PubMed2005

Touch-induced visual illusion.

Although vision is considered the dominant modality, recent studies demonstrate the influence of other modalities on visual perception. For example, in the sound-induced flash illusion, two auditory stimuli cause one visual flash to be perceived as two. We report an extension of the sound-induced flash illusion to the tactile-visual domain, yielding the touch-induced flash illusion. Observers reported seeing two flashes on the majority of trials when a single flash was presented concurrently with two task-irrelevant brief tactile stimuli. Somatosensory stimulation changed the sensitivity (d') of detecting visual stimuli, which suggests that the observed effect is at least partly due to perceptual interactions. Together with other recent findings, these results challenge the notion that the processing of visual information is independent of activity in other modalities.

Analysis of Variance↗
PubMed2001

Early head movements elicited by visual stimuli or collicular electrical stimulation in the cat.

During the course of previous recordings of visually-triggered gaze shifts in the head-unrestrained cat, we occasionally observed small head movements which preceded the initiation of the saccadic eye/head gaze shift toward a visual target. These early head movements (EHMs) were directed toward the target and occurred with a probability varying between animals from 0.4% to 16.4% (mean=5.2%, n=11 animals). The amplitude of EHM ranged from 0.4 degrees to 8.3 degrees (mean=1.9 degrees ), their latency from 66 to 270 ms (median=133 ms) and the delay from EHM onset to gaze shift onset averaged 183+/-108 ms (n=240). Their occurrence did not depend on visual target eccentricity in the studied range (7-35 degrees ), but influenced the metrics and dynamics of the ensuing gaze shifts (gain and velocity reduced). We also found in the two tested cats that low intensity microstimulation of the superior colliculus deeper layers elicited a head movement preceding the gaze shift. Altogether, these results suggest that the presentation of a visual target can elicit a head movement without triggering a saccadic eye/head gaze shift. The visuomotor pathways triggering these early head movements can involve the deep superior colliculus.

Animals↗