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PubMed1993

Effects of intermodality change on electrodermal orienting and on the allocation of processing resources.

Two experiments studied the effects of intermodality change on electrodermal responses and on reaction time to a secondary task probe stimulus after 24 habituation training trials with either a tone or a vibrotactile stimulus. The probe was a visual stimulus of 500 ms duration, and within-stimulus probes occurred 300 ms following stimulus onset. Experiment 1 crossed change versus no change with modality of the training stimulus. Skin conductance responses (SCRs) were larger in the experimental group than in the control on the test trial, and in the experimental group, test trial responses were larger than those on the first training trial. Probe reaction time was slower on the test trial in the experimental group than in the control, and within-stimulus probe reaction time was slower than interstimulus interval reaction time early in the habituation series. Experiment 2 crossed change versus no change with the presence of a secondary task. Test trial SCRs were larger in the experimental group than in the control, regardless of whether or not the secondary task was present. In addition, test trial responses in the experimental group were larger than those on the first training trial in both the task and no-task conditions. Within the task condition, reaction time was slower in the experimental condition than in the control on the test trial. In addition, reaction time in the experimental condition was slower during the change trial than during the first training stimulus. The data provide difficulties for noncomparator theories of habituation and seem to be most easily explained by theories of habituation that emphasize the importance of an extrapolatory process.

Acoustic Stimulation↗
PubMed1997

Circadian rest-activity rhythms in demented and nondemented older community residents and their caregivers.

OBJECTIVE: Disruptive nocturnal behaviors (DNBs) of older people often threaten the caregiving arrangements on which their community tenure depends. Dementing disorders are especially prone to result in disrupted sleep and agitated behaviors ("sundowning"). The objective here was to develop an objective correlate of DNBs, by which their severity and effects on caregivers can be measured. DESIGN: Quantitative comparison of subjective sleep and motor activity patterns in older people and their caregivers. It was hypothesized that older people with reported DNBs would be more motorically active at night than their caregivers. SETTING: Subjects' homes. PARTICIPANTS: Twenty-five demented and 18 nondemented older day-care participants and their paired caregivers. MEASUREMENTS: Older subjects and caregivers simultaneously kept daily sleep logs and recorded wrist motor activity every .5 minute for 9 days. A novel method was devised to identify and exclude from analysis periods when the activity monitor was not being worn. Such periods were common. Activity data were analyzed by computing hourly means and by fitting cosine models by least squares. RESULTS: Demented older people were not significantly more active at night than their caregivers, though group differences varied by time of night. They were significantly less active in the daytime than were their caregivers. Nondemented older people were significantly more active at night than their caregivers and were as active by day as their caregivers. The caregivers of demented and nondemented older people had similar rest-activity patterns. The mean amplitudes of cosine models were smaller in the older adults. Acrophases (peaks) fell between 2 and 3 pm and did not differ significantly among the groups. CONCLUSIONS: As a result of increased nighttime motor activity and decreased daytime activity, rest-activity rhythms were flatter in older adults than in caregivers. This was not explained fully by age and does not necessarily imply that the output of a circadian pacemaker was low. Decreased daytime activity may have resulted from deficient physical stimulation or frailty. Frailty may also explain why nighttime activity was not more elevated in the demented older people. Increased nighttime activity is probably explained by depression, sleep-schedule disturbances, restless legs, or other sleep disorders. Judging by their shared variations of activity, caregivers interacted mainly with the demented older people at bedtime and at rising time in the morning.

Aged↗
PubMed1999

Molecular mechanisms of cell death in the ear.

Damage to sensory cells and neurones of the inner ear, induced by ototoxic drugs, physical stimulation, or even normal aging, occurs by mechanisms that are not yet fully elucidated. However, for the individual the consequent loss of hearing can be devastating. This the concept that, in some instances, this brain cell death may be preventable has provided an exciting and novel route to thwart the degenerative process. Signals that trigger cell death can be as diverse as the removal of essential growth factors, damage by exogenous toxins (including ototoxic drugs), free radicals, and excitotoxins. An important facet to the newly discovered death cascade is that it can be halted, and such interventions may rescue the dying cell. The question now remains whether any of the cell death observed on ototoxic or noise-induced hearing loss occurs by an "active" programmed mechanism (apoptosis), as physiological cell death does in the developing ear, and if so, whether it can be prevented.

Apoptosis↗
PubMed1973

Spinal interneurones involved in presynaptic controls of supraspinal origin.

1. Interneurones presenting heterotopic and heterosensory convergence have been identified in laminae VI-VII of the lumbar dorsal horn in the cat. Stimulation of the hind limbs sometimes induced a bimodal response, but we considered only the late convergent discharge.2. The fact that response latencies are longer to hind limb than to forelimb stimulation at this level suggests the intervention of a supraspinal loop in the activation of spinal convergent units. This hypothesis is supported by the relationship between the excitability of supraspinal structures and the discharge intensity of convergent cells as well as by the absence of long latency responses in the spinal preparation.3. Electrophysiological and pharmacological evidence discloses a strong relationship between convergent unit discharges and the occurrence of dorsal root potentials to cortical, heterosegmental and heterosensory stimulation.4. It is suggested that convergent units receive information of supraspinal origin and exert control over sensory input to the cord via primary afferent depolarization.

Acetates↗
PubMed1975

Receptive fields in cat superior colliculus after visual cortex lesions.

1. The superior colliculus has been studied in intact cats and in cats with visual cortex lexions by recording the responses of single tectal units to visual stimuli. 2. Three classes of units have been identified in the superficial layers of the colliculus in these visually decorticate cats. 3. One class, comprising 5% of the units studied, has receptive fields organized concentrically in a manner similar to retinal ganglion cells. 4. The second class, comprising 12% of the units studied, responds to stimulus velocities over 300/sec, responds well to both small and large stimuli, and can be driven by strobe flashes at frequencies up to 35--40/sec. These units are termed 'flicker' cells. 5. The third class comprising 83% of the units studied, responds best to stimuli which are not larger than the activating region of the receptive field, moving at relatively low velocities. These units show strong suppressive surrounds which are sensitive to higher velocities of stimulus movement than the central activating region. Responses from the activating region in these units are dramatically inhibited by flickering dhanges in the level of background illumination. 6. In intact cats few units are found which are strongly inhibited by background flicker. 7. It is suggested that a high-velocity sensitive element such as the 'flicker' cell or phasic retinal ganglion cell is responsible for the flicker-induced inhibition of collicular units in the visually decorticate cat.

Action Potentials↗
PubMed1984

Sensory-motor processing in substantia nigra pars reticulata in conscious cats.

Extracellular recordings were made with chronically implanted micro-electrodes from 109 substantia nigra neurones in conscious cats. Ninety-six of 109 neurones met the criteria of presumed non-dopaminergic pars reticulata (s.n.r.) neurones. Background discharge, in animals in a state of relaxed wakefulness and in the absence of overt movements, was in the range of 11-37 impulses/s, mean 19.2 impulses/s. The discharges of fifty-two of ninety-six neurones tested were modified by innocuous mechanical skin stimulation. Neurones responded chiefly to stimuli delivered to the contralateral body side. Responses generally comprised net excitation and occurred with short latency (range 10-34 ms; mean 17.3 ms). Convergence from both forelimbs or the contralateral fore- and hind limbs was evident in a few cases. One-fourth (twenty-four out of ninety-six) of the s.n.r. neurones tested were sensitive to passive manipulation of limb joints in the quiet, conscious cat and responded exclusively to angular displacement of one contralateral joint. Responses were directional and phasic. None of the s.n.r. neurones tested responded to clicks and/or light flashes. However, stimuli moving across the contralateral visual field substantially modified the discharge rate of ten out of ninety-six s.n.r. neurones. Responses were directional and invariably associated with eye movements. Animals were also trained to walk on a treadmill and to perform certain self-generated limb movements. S.n.r. neurones with a receptive field on a limb regularly showed modulations in discharge during locomotion, phase-related to the step cycle, and also short-latency responses during disturbance of such movements. Ten out of ninety-six s.n.r. neurones discharged almost exclusively prior to and during self-generated movements of a single limb. Their most powerful modulations in firing rate occurred, whenever an animal tried to overcome an external impediment or to resist an imposed movement. These observations on s.n.r. neurones, taken together with previous findings on nigral influences on spinal motor circuitry, indicate that the s.n.r. represents an output station of the basal ganglia which is involved in the subconscious processing of convergent multimodal sensory information and which participates in setting appropriate gains and biasses of spinal motor neuronal systems to adequately deal with changing motor requirements.

Acoustic Stimulation↗
PubMed1990

Localization and responses of neurones in the parieto-insular vestibular cortex of awake monkeys (Macaca fascicularis).

1. In four Java monkeys (Macaca fascicularis) 152 vestibular neurones were recorded in the parietal cortex located in the upper bank of the lateral sulcus near the posterior end of the insula. We called this region parieto-insular vestibular cortex (PIVC). PIVC extends about 6-8 mm in the anterior-posterior direction from the posterior part of the insula into the retroinsular region (stereotaxic co-ordinates: anterior 4-12 mm, lateral 16-19 mm and vertical 3-6 mm). 2. About two-thirds of the neurones recorded from this region responded to vestibular stimuli; the non-vestibular neurones responded predominantly to somatosensory stimulation of the neck and shoulder region. The PIVC area is a polysensory field, since almost all vestibular neurones were also activated by somatosensory and visual stimuli. Large-field optokinetic stimulation was the most effective visual stimulus. 3. With vestibular stimuli, responses to angular acceleration were dominant; steady tilt in darkness rarely led to any change in neuronal spontaneous activity. Of sixty-four neurones tested by rotation in more than one plane, fifty-four responded to excitation of semicircular canal receptors aroused by rotation in more than one of the three experimental planes (roll, yaw, pitch). Compared with vestibular brain stem units PIVC neurones discharged with a higher variability. 4. In the responses to horizontal rotation of the animal 38% type I, 53% type II and 9% type III units were recorded (classification according to Duensing & Schaefer, 1958). The gain measured with horizontal sinewave rotation was lower by a factor of about 4 in PIVC neurones as compared with the responses of vestibular neurones in the brain stem or thalamus (VPL). The phase response characteristics and the gain increase with increasing sinewave stimulus frequency, however, were in the same range as observed in neurones of the afferent vestibular system. 5. When the vestibular responses to sinusoidal rotation were tested in all three experimental planes (yaw, roll, pitch), the response strength as expressed by the amplitude of the peristimulus time histograms (PSTHs) differed for the three rotational planes. For different units the relative sensitivity to rotation in each of the three planes also differed. We concluded from this observation that different PIVC units had different optimum sensitivity planes for rotation with respect to the head co-ordinates, whereby all possible planes are represented.

Animals↗
PubMed1990

Vestibular neurones in the parieto-insular cortex of monkeys (Macaca fascicularis): visual and neck receptor responses.

1. One hundred and fifty-two vestibularly activated neurones were recorded in the parieto-insular vestibular cortex (PIVC) of four awake Java monkeys (Macaca fascicularis): sixty-two were tested systematically with visual stimulation and seventy-nine were tested with various somatosensory stimuli. With very few exceptions all vestibular neurones tested responded to visual and somatosensory stimulation, therefore being classified as polymodal vestibular units. 2. A most effective stimulus for all fifty-eight visually activated PIVC units was movement of a large structured visual pattern in an optimal direction. From forty-four units responsive to a horizontally moving optokinetic striped drum, twenty-nine were activated with optokinetic movement in the opposite direction to the activating vestibular stimulus ('synergistic' response), thirteen were activated optokinetically and vestibularly in the same direction ('antagonistic' responses) and two were biphasic. The gain of the optokinetic response to sinusoidal stimulation (average 0.28 (impulses s-1) (deg s-1)-1 at 0.2 Hz, 56 deg amplitude) was in a range similar to that of the vestibular gain at low frequencies. At 1 Hz some units only showed weak optokinetic responses or none at all, but the vestibular response was still strong. 3. With different 'conflicting' or 'enhancing' combinations of optokinetic and vestibular stimulation no generalized type of interaction was observed, but the responses varied from nearly 'algebraic' summation to no discernible changes in the vestibular responses by additional optokinetic stimuli. With all visual-vestibular stimulus combinations the responses to the vestibular stimulus remained dominant. 4. The optokinetic preferred direction was not related to gravitational coordinates since the optokinetic responses were related to the head co-ordinates and remained constant with respect to the head co-ordinates at different angles of steady tilt. 5. Almost all PIVC units were activated by somatosensory stimulation, whereby mainly pressure and/or movement of neck and shoulders (bilateral) and movement of the arm joints elicited vigorous responses. Fewer neurones were activated by lightly touching shoulders/arms or neck, by vibration and/or pressure to the vertebrae, pelvis and legs. 6. A most effective somatosensory stimulus was sinewave rotation of the body with head stationary. The gain of this directionally selective neck receptor response was in the range of vestibular stimulation. Interaction of vestibular and neck receptor stimulation was either of a cancellation or facilitation type.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1992

Classification of preganglionic neurones projecting into the cat cervical sympathetic trunk.

1. The spontaneous and reflex activity patterns of 167 single preganglionic axons dissected from the cervical sympathetic trunk were examined in chloralose-anaesthetized cats. Each neurone was classified into one of four major groups, on the basis of three principal criteria: the presence or absence of significant cardiac rhythmicity of the activity, the response to noxious stimulation of the skin, and the coupling of its activity to central inspiratory drive (phrenic nerve activity). Most neurones were also subjected to additional tests, which included carotid chemoreceptor stimulation, nasopharyngeal probing, systemic hypercapnia (ventilation with 8% CO2), hyperventilation, adrenaline-induced blood pressure rises and retinal illumination. 2. Group I neurones (n = 69; 41%) showed significant cardiac rhythmicity, indicating strong baroreceptor control. Most (54/69) were excited by noxious stimuli, the rest being unaffected. Their activity showed variable degrees of excitatory coupling to the central inspiratory drive, and was enhanced by hypercapnia (35/39). Their responses to stimulation of arterial chemoreceptors (12/15) and nasopharyngeal receptors (24/35) were excitatory. 3. Group II neurones (n = 39; 23%) were inhibited by noxious stimulation of skin. With nine exceptions, they showed no significant cardiac rhythmicity, although they were weakly inhibited by an adrenaline-induced blood pressure rise. Their coupling to central inspiratory drive was weak or absent, and their responses to hypercapnia and hyperventilation were variable. By contrast to other groups, they were inhibited by both chemoreceptor stimulation (9/10) and nasopharyngeal stimulation (17/18). 4. Group III neurones (n = 33; 20%) showed no significant cardiac rhythmicity, but their activity was closely coupled to central inspiratory drive. They were inhibited by hyperventilation (9/9) and excited by hypercapnia (20/21), but only fired during the central inspiratory phase and sometimes during late expiration. Their responses to noxious stimulation (28/33), chemoreceptor stimulation (8/11) and nasopharyngeal probing (24/24) were excitatory, but the induced activity was 'gated' by the respiratory cycle, occurring primarily during inspiration and avoiding the postinspiratory phase. 5. Group IV neurones (n = 26; 16%) showed no significant cardiac or respiratory related activity and were either excited (n = 22) or unaffected (n = 4) by noxious stimuli. One of the latter and three group II neurones were inhibited by retinal illumination; thirty-one other neurones of all classes were unaffected. 6. Approximately 45% of thoracic sympathetic neurones were silent under the experimental conditions. About 25% of these could be recruited by systemic hypercapnia leaving 34% without spontaneous and reflex activity.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed2003

Area 21a of cat visual cortex strongly modulates neuronal activities in the superior colliculus.

We have examined the influence of cortico-tectal projections from one of the pattern-processing extrastriate visual cortical areas, area 21a, on the responses to visual stimuli of single neurones in the superior colliculi of adult cats. For this purpose area 21a was briefly inactivated by cooling to 10 degrees C using a Peltier device. Responses to visual stimuli before and during cooling as well as after rewarming ipsilateral area 21a were compared. In addition, in a subpopulation of collicular neurones we have studied the effects of reversible inactivation of ipsilateral striate cortex (area 17, area V1). When area 21a was cooled, the temperature of area 17 was kept at 36 degrees C and vice versa. In the majority of cases (41/65; 63%), irrespective of the velocity response profiles of collicular neurones, inactivation of area 21a resulted in a significant decrease in magnitude of responses of neurones in the ipsilateral colliculus and only in a small proportion of cells (2/65; 3.1%) was there a significant increase in the magnitude of responses. Inactivation of area 21a resulted in significant changes in the magnitude of responses of collicular cells located not only in the retino-recipient layers but also in the stratum griseum intermediale. In most cases, reversible inactivation of area 17 resulted in a greater reduction in the magnitude of responses of collicular cells than inactivation of area 21a. Reversible inactivation of area 21a also affected the direction selectivity indices and length tuning of most collicular cells tested.

Action Potentials↗
PubMed2003

Compensatory increase of the cervico-ocular reflex with age in healthy humans.

The cervico-ocular reflex (COR) is an ocular stabilization reflex that is elicited by rotation of the neck. It works in conjunction with the vestibulo-ocular reflex (VOR) and the optokinetic reflex (OKR) in order to prevent visual slip over the retina due to self-motion. The gains of the VOR and OKR are known to decrease with age. We have investigated whether the COR, a reflexive eye movement elicited by rotation of the neck, shows a compensatory increase and whether a synergy exists between the COR and the other ocular stabilization reflexes. In the present study 35 healthy subjects of varying age (20-86 years) were rotated in the dark in a trunk-to-head manner (the head fixed in spaced with the body passively rotated under it) at peak velocities between 2.1 and 12.6 deg s-1 as a COR stimulus. Another 15 were subjected to COR, VOR and OKR stimuli at frequencies between 0.04 and 0.1 Hz. Three subjects participated in both tests. The position of the eyes was recorded with an infrared recording technique. We found that the COR-gain increases with increasing age and that there is a significant covariation between the gains of the VOR and COR, meaning that when VOR increases, COR decreases and vice versa. A nearly constant phase lag between the COR and the VOR of about 25 deg existed at all stimulus frequencies.

Adult↗
PubMed1972

Habituation and dishabituation: interactions between peripheral and central nervous systems in Aplysia.

The withdrawal response of the isolated siphon of Aplysia habituates to a light stimulus and dishabituates to a tactile stimulus, and vice versa, with or without connections to the central nervous system. The peripheral nervous system can dishabituate or enhance the response mediated by the central nervous system and vice versa. Normally the adaptive siphon withdrawal response of the intact animal must be mediated by the integrated activity of the peripheral and central nervous systems.

Action Potentials↗
PubMed1973

Evoked potential correlates of signal recognition between and within modalities.

Electrical responses evoked by clicks, flashes, changes in noise level, and changes in light level were recorded from the scalps of human subjects set to detect one of the stimuli. An early negative component of the evoked responses reflects selection between sensory modalities, whereas the later positive component reflects a more complex intramodal discrimination.

Acoustic Stimulation↗
PubMed1974

Paradoxical effects after microinjection of morphine in the periaqueductal gray matter in the rat.

Paradoxical, concurrent hyper-and hyporeactivity of a profound nature to specific stimuli occurred when 10 micrograms of morphine was microinjected bilaterally into the periaqueductal gray matter of the rat brain. Both effects at this site were dose-dependent. The hyperreactivity (to previously neutral auditory and visual stimuli) was obtained only with intracerebrally injected morphine and never with intraperitoneally injected morphine or with other opiates administered either way. Rapid tolerance to toxic doses of morphine developed at this site, as well as cross tolerance of the hyporeactivity to painful stimuli between routes (intracerebral to intraperitoneal) of morphine administration. Both the hyper- and hyporeactivity were fully reversible by intracerebral injection of naloxone in the periaqueductal gray. Thus, the periaqueductal gray appears to be a major pathway for morphine action.

Acoustic Stimulation↗
PubMed2003

Cognitive modulation of the cerebral processing of human oesophageal sensation using functional magnetic resonance imaging.

BACKGROUND: While cortical processing of visceral sensation has been described, the role that cognitive factors play in modulating this processing remains unclear. AIM: To investigate how selective and divided attention modulate the cerebral processing of oesophageal sensation. METHODS: In seven healthy volunteers (six males, mean age 33 years; ranging from 24 to 41 years old) from the general community, phasic visual and oesophageal (non-painful balloon distension) stimuli were presented simultaneously. During the selective attention task, subjects were instructed to press a button either to a change in frequency of oesophageal or visual stimuli. During a divided attention task, subjects received simultaneous visual and oesophageal stimuli and were instructed to press a button in response to a change in frequency of both stimuli. RESULTS: Selectively focussing attention on oesophageal stimuli activated the visceral sensory and cognitive neural networks (primary and secondary sensory cortices and anterior cingulate cortex respectively) while selective attention to visual stimuli primarily activated the visual cortex. When attention was divided between the two sensory modalities, more brain regions in the sensory and cognitive domains were utilised to process oesophageal stimuli in comparison to those employed to process visual stimuli (p=0.003). CONCLUSION: Selective and divided attention to visceral stimuli recruits more neural resources in both the sensory and cognitive domains than attention to visual stimuli. We provide neurobiological evidence that demonstrates the biological importance placed on visceral sensations and demonstrate the influence of cognitive factors such as attention on the cerebral processing of visceral sensation.

Adult↗
PubMed1994

Reflex myoclonus in olivopontocerebellar atrophy.

The presence of reflex myoclonus in response to touching and pin-pricking the wrist or stretching the fingers and to photic stimulation was assessed in 24 patients with a presumed diagnosis of olivopontocerebellar atrophy (OPCA) and in 30 age matched control subjects. Reflex myoclonus to soma-esthetic stimulation was found in 23 patients and in none of the controls. Photic myoclonus was present in 12 patients and in none of the controls. Electrophysiological study of the reflex myoclonus showed enhanced (> 10 microV) somatosensory evoked potentials and an associated reflex electromyographic discharge (C-wave) in 15 patients. These findings indicate that reflex myoclonus is common in OPCA and probably of cortical origin.

Atrophy↗
PubMed1995

Responses of single neurons in amygdala to interoceptive and exteroceptive stimuli in conscious cats.

The amygdala is critical for behavioral arousal and must therefore integrate a wide variety of inputs. We examined sensory inputs and the degree of convergence to single neurons in the amygdala in conscious freely moving cats. A pressor stimulus elicited responses, predominantly inhibitory, in one-half of the amygdalar neurons tested. Most neurons in the central and basal nuclei responded to carotid chemoreceptor activation typically with an excitation. Almost one-half of all amygdalar neurons tested, particularly in the central nucleus, received orthodromic input from the locus ceruleus, the substantia nigra, and/or the contralateral central nucleus of the amygdala. Exteroceptive sensory stimulation with optic, acoustic, tactile, and olfactory stimuli elicited responses in 33, 55, 39, and 59% of amygdalar neurons, respectively. Two-thirds of the neurons tested with more than one external stimulus modality responded in the same manner to the various stimuli (usually excitation), demonstrating a convergence of exteroceptive stimuli on single amygdalar neurons, particularly in the basal nucleus. Spontaneous and induced behavioral arousal elicited responses in 92 and 86% of neurons, respectively. Most neurons responded to multimodal exteroceptive stimuli and behavioral arousal in the same manner. We suggest that amygdalar inputs are highly varied and, in many cases, relatively nonspecific and that the amygdala integrates a large number of external and internal sensory modalities to regulate autonomic and behavioral responsiveness to various stimuli.

Amygdala↗