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PubMed1987

Interhemispheric communication of visual learning: a developmental study in 3-6-month old infants.

Infants aged 12-26 weeks (3-6 months) were presented with a visual category discrimination learning task (normal vs scrambled faces) in the right or left visual field. Once they had reached the learning criterion, they were tested for transfer to the untrained visual field in order to establish whether visual experience can be communicated to the opposite hemisphere. Transfer of learning was found to occur in infants aged 19-26 weeks but not in younger ones. Neural pathways possibly forming the channels for this communication are discussed.

Aging↗

PubMed1991

Absence of disconnexion syndrome in callosal agenesis and early callosotomy: brain reorganization or lack of structural specificity during ontogeny?

Four acallosal subjects, one child, aged 5, and three adults, as well as five epileptic patients who underwent callosotomy between the ages of 6-21 years, were tested on a variety of intra- and intermanual tasks in a study aimed at elucidating the developmental aspects of callosal plasticity. The performance of the clinical sample was compared to that of 48 normal children, aged 5-12 years, an age span generally considered to coincide with the final stages of callosal maturation. As previously reported, interhemispheric integration improved with increasing age in the normal sample. The two patients having undergone callosotomy in childhood performed as well as their normal peers, whereas the three others who had the operation in late adolescence or adulthood showed the typical disconnexion deficits reported in the literature. The acallosal subjects, including the youngest one, outperformed all groups. We speculate that the remarkable plasticity seen in the acallosals and the young callosotomized patients may be related to a critical period in development coinciding with a phase of synaptic overproduction and redundancy that would favor the reinforcement of alternative neural pathways. The compensatory mechanisms appear to become more limited in late adolescence when synaptic distribution presumably assumes adult patterns.

Adolescent↗

PubMed1982

Pigment mutations associated with altered circadian rhythms in mice.

Mammalian albinism is known to alter neural pathways, reduce retinal pigment, and affect diverse behaviors. Mammalian circadian rhythms have been shown to depend on visual pathways, respond to light intensity and regulate many behaviors. Here we show that mice homozygous for the recessive albino or pinkeye-dilute mutations display shorter circadian rhythms than pigmented controls. We conclude that these pigment loci, or closely linked loci, influence the expression of circadian rhythms in mice.

Animals↗

PubMed1985

The importance of olfactory bulb noradrenalin for maternal recognition in sheep.

Herds of grazing mammals characteristically produce precocial offspring in synchrony, and it is therefore important for the mother to form a rapid recognition of her own offspring to distinguish them from others. In sheep, the ewe forms such a selective bond with her lamb within 2-4 hours of parturition, a bond which is primarily dependent on olfactory sensory recognition. Here we report that the neuronal mechanism whereby the olfactory "imprint" is made is dependent on the centrifugal noradrenergic projections to the olfactory bulbs. Lesioning of this neural pathway prevents the ewe from forming a selective bond with her own lamb, enabling her to adopt alien lambs.

Animals↗

PubMed1987

Effect of localized changes in scrotal and trunk skin temperature on the demand for radiant heat by pigs.

Localized warming of the scrotal skin to 42 degrees C decreased the number of operant responses for reinforcements of radiant heat when young pigs were exposed to cold (15 degrees C); warming a similar area of the skin on the trunk had no effect on behaviour. The decrease in responding for heat was more pronounced immediately after a meal than when animals were observed 22 hr after their last meal. Cooling the scrotal or trunk skin to 20 degrees C did not modify operant behaviour. It is concluded that the thermal signal from the scrotum is in disproportion to the surface area of the scrotum indicating either increased concentration of thermal receptors per surface unit of the skin, or processing and amplifying the thermal information along the scrotal-brain neural pathway. The significance of the elicited changes in the demand for radiant heat is discussed in relation to the control of testes temperature.

Animals↗

PubMed1987

Pubertal decline in maternal responsiveness in Long-Evans rats: maturational influences.

Latency to onset of maternal behavior increases progressively from the weanling to the peripubertal period in female and male Long-Evans rats. Gonadectomy or hypophysectomy on day 21 had no influence on the pubertal decline in maternal responsiveness. Apparently, inhibitory neural pathways mature which are independent of pituitary hormonal influences.

Animals↗

PubMed1988

Hypothalamic food intake regulating areas are involved in the homeostasis of blood glucose and plasma FFA levels.

The hypothalamus fulfills multiple functions, e.g., integration of food and water ingestion, various forms of social behavior and physiological neuroendocrine activities. Hypothalamic areas, particularly the ventromedial, lateral and paraventricular areas (VMH, LHA and PVN respectively), that contribute to the regulation of food intake are also involved in the regulation of blood glucose and plasma free fatty acid (FFA) levels. This regulation is controlled both directly via neural pathways and indirectly by hormones, e.g., insulin, glucagon, norepinephrine (NE) and epinephrine (E). A description is presented of the intrahypothalamic connections and the pathways between the hypothalamus and the motor areas of both the sympathetic system in the spinal cord (the intermediolateral column IML) and the parasympathetic system in the brainstem (the dorsal motornucleus of the vagus and the nucleus ambiguus). Noradrenergic stimulation of the LHA, VMH and PVN can alter blood glucose, plasma FFA and insulin levels independently of each other, e.g., noradrenergic stimulation of the VMH leads to an increase of insulin, glucose and FFA. Exercise induced increases of glucose are suppressed by alpha-adrenergic blockade of the LHA, VMH and PVN. Alpha-adrenergic blockade of the VMH during exercise causes an exaggerated increase of plasma FFA whereas alpha-blockade of both the LHA and PVN does not change the normal exercise induced increase of plasma FFA. The apparent contradiction that both adrenergic stimulation and adrenergic blockade of the VMH result in an increase in FFA may be explained by assuming postsynaptic alpha- and beta-adrenergic receptors in the VMH controlling glucose and FFA release respectively and FFA release and presynaptic inhibitory alpha-adrenergic receptors.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1990

Intestinal infusion of a liquid diet alters CCK and NPY concentrations in specific brain areas of rats.

Cholecystokinin (CCK) and neuropeptide Y (NPY) have been implicated in the control of food intake in a number of species. This study was carried out to determine 1) whether nutrient-related stimulation of the upper small intestine could activate central CCK and NPY neuronal systems, resulting in changes in concentration of these peptides in specific brain areas, and 2) the influence of the circadian cycle on nutrient-related effects. Four groups of rats received treatments of either 1.0 ml saline (S) or Ensure liquid diet (E) infused into the duodenum either during the dark (D) or light (L) phase of the circadian cycle. CCK and NPY concentrations in extracts of specific brain areas were measured by RIAs. CCK concentration in the supraoptic n. (SON) was higher in D than in L, regardless of infusion treatment, and in the dorsal parabrachial n. area (DPN), CCK concentration was higher in E than S infused rats, regardless of circadian phase. CCK concentration in the dorsal motor vagal n. area (DMV) was higher in E, but only during L. NPY concentration was higher in DPN and paraventricular n. areas (PVN) and lower in the suprachiasmatic n. area (SC) after E, regardless of circadian phase. The changes in concentration of CCK and NPY in specific brain areas in response to food in the upper intestine suggest that nutrient-related signals from the intestine can activate specific CNS CCK and NPY-containing neural pathways.

Animals↗

PubMed1991

Dissociation of tactile and acoustic components in air puff startle.

Tactile (air puff) or acoustic startle stimuli elicit behavioral (motor) and complex cardiovascular responses which include pressor as well as cardiac decelerative and accelerative responses. An acoustic component of the air puff stimulus (12.5 psi) was identified. Studies were conducted to separate the contributions of both stimulus modalities to the observed responses. The acoustic component was approximated with a wide-spectrum 97-dB white-noise stimulus. This acoustic stimulus failed to evoke heart rate responses but did yield motor and pressor responses. In a second approach, tympanic membrane rupture (TMR) was used to interrupt acoustic sensory stimuli. TMR fully abolished the motor and pressor responses to acoustic startle. With air puff startle, while TMR severely attenuated the motor response it only decreased slightly the pressor and cardiac accelerative responses and failed to influence the cardiac decelerative component. Our results indicate that air puff startle contains both tactile and acoustic modalities. Further, the motor response is largely driven by the acoustic modality since TMR abolished this response elicited by either acoustic or tactile stimulation. More importantly, motor and cardiovascular responses to startle may be separated through discrimination of afferent stimuli suggesting either differences in neural pathways for acoustic and tactile stimuli or a differential dependency of the various responses on stimulus characteristics.

Acoustic Stimulation↗

PubMed1992

Olfactory bulb removal affects partner preference development and estrus induction in female prairie voles.

In female prairie voles (Microtus ochrogaster) bilateral olfactory bulbectomy reduced affiliative behavior, as measured by social contact, and prevented the formation of partner preferences. Unilateral olfactory bulb removal did not significantly influence affiliative behavior, but did inhibit partner preferences. Bilateral, but not unilateral, bulbectomy significantly reduced the proportion of females exhibiting behavioral estrus following male exposure. In contrast to affiliative and sexual behavior, parental behavior was not significantly affected by either bilateral or unilateral olfactory bulbectomy. These results suggest that divergent sensory-neural pathways underlie social, sexual, and parental behaviors in this species.

Aggression↗

PubMed1995

Mercaptoacetate-induced feeding is impaired by central nucleus of the amygdala lesions.

Systemic administration of mercaptoacetate (MA) blocks beta oxidation of fatty acids and stimulates food intake. The present experiment examined MA-induced feeding in rats with bilateral lesions of the central nucleus of the amygdala (CNA) and sham-operated controls. Food intake was measured for 6 h immediately following i.p. injection of 400, 600, or 800 mumol/kg of MA or saline. Feeding was also measured in these rats in response to 2-deoxy-D-glucose (2DG) (100, 200, and 300 mg/kg, SC), a glucose analogue that competitively inhibits glucose utilization. We found that CNA lesions blocked feeding in response to all three doses of MA. Feeding in response to 2DG was significantly reduced, but not abolished, by the lesion. These findings suggest that the CNA is a crucial component of the neural pathway for feeding in response to MA and may also participate in 2DG-induced feeding.

Amygdala↗

PubMedDate not supplied

Liver denervation attenuates the hypophagia produced by an imbalanced amino acid diet.

We observed previously that totally liver denervated (TLD) rats consumed more of an imbalanced amino acid diet (IAAD) than sham-operated controls (CON). For the present study rats were either CON, TLD, had only the hepatic-vagal branch cut (HVX), or had all nerves on the hepatic artery and portal vein removed (HAPV) (n = 10-11). The rats were prefed a purified basal diet for 9 days then switched to an isoleucine IAAD for 7 days. On days 2-5 all experimental groups consumed more (p < 0.05) of the IAAD than the CON; they also showed less (p < 0.01) weight loss on days 3-7. This experiment showed that either total or partial liver denervations enhanced the intake of an IAAD compared to CON. However, when one considers the anatomical arrangement of the nerves and the surgery technique employed the vital neural pathway may involve the hepatic vagal branch.

Amino Acids↗

PubMed1983

Interocular transfer of colour-contingent threshold elevation.

Following adaptation to a moving coloured stimulus pattern the contrast threshold for detecting a similar moving pattern is raised. Threshold elevation is greatest when the adaptation and test patterns have the same direction of motion and the same colour. Unlike most other colour-contingent aftereffects, colour-specificity is preserved under dichoptic viewing conditions. The results are discussed in terms of possible underlying neural pathways in the visual system.

Adaptation, Ocular↗

PubMed1985

Adaptation to apparent motion.

A spot alternating between two positions can produce apparent motion (AM). Following prolonged inspection, the AM degenerates into flicker. This adaptation effect was found to depend on spacing and timing; the probability of seeing motion during a 30-sec inspection period declined linearly with log spatial separation (over a range from 0.1 to 1 deg), and with log alternation rate (over a range from 2 to 4.5 Hz). Cross-adaptation, in which subjects were adapted to one alternation rate and tested at another, showed that low alternation rates gave stronger motion signals than high rates did. Adaptation to real motion (RM) strongly suppressed AM, which suggests that AM must be stimulating the same neural pathways as RM. Flickering spots (i.e. in-phase flicker) produced less adaptation than did a spot alternating between two positions (i.e. counterphase flicker), so the adapting mechanism must be responding to relative temporal phase. Embedding the adapting spots in configurations of other spots, which altered the pattern of perceived adapting motion without altering the local retinal stimulation, minimized the adaption, so the adapting mechanism must be responding to the path of seen motion. Adaptation can be used to measure the strength of AM and shows that AM is strongest for small separations, low alternation rates and high luminance contrast.

Adaptation, Ocular↗

PubMed1985

Origin of the oscillatory potentials in the primate retina.

The current source and sink profiles of the oscillatory potentials (OPs) of the primate (macaque) electroretinogram (ERG) were studied. The intraretinal local ERG (LERG) and the local resistivity were recorded with a bipolar microelectrode in the intact macaque eye in response to a 10 deg and full field stimulus. A statistical method, a principle component analysis, was performed on high pass digitally filtered LERGs to extract and more closely study the oscillatory components of the LERG's at a number of electrode depths in the retina. The OPs were found to represent radial current flow and to have a current distribution different from those of the receptor and b-wave components. They are generated more proximal than the a- and b-waves, most probably by the bipolar cells. However, the interplexiform cell cannot be excluded as a generator. If so, the OPs should represent activity in a feed-back neural pathway in the inner part of the retina, also in the primate. The OPs can be used to monitor the inner neuronal layer but further differentiation in depth regarding consecutive peaks is not possible.

Animals↗

PubMed1991

The relative contributions of pre-neural and neural factors to areal summation in the fovea.

In order to determine the relative contributions of pre-neural and neural factors to areal summation in the fovea, measurements of Ricco's area were made. These were compared to the results of an ideal-observer analysis which incorporated only pre-neural factors, up to the level of the photoreceptor. The comparison indicated that Ricco's area in the fovea is largely (if not completely) accounted for by pre-neural factors. Thus, our results, in agreement with the recent analysis of contrast sensitivity by Banks, Geisler and Bennett (1987; Vision Research, 27, 1915-1924), are consistent with the hypothesis that a neural pathway exists which consists of units whose center mechanisms sum over only a single cone or a single row of cones. Our results also imply that the quantum efficiency for detection is constant for test areas up to 256 min2, once the effects of the optics and receptor aperture are factored out.

Adaptation, Ocular↗

PubMed1992

Monochromatism determined at a long-wavelength/middle-wavelength cone-antagonistic locus.

The foveal increment threshold spectral sensitivity function for a 500 msec raised cosine stimulus without spatial edges exhibits a sharp drop or "notch" in sensitivity that coincides with the wavelength of a long-wavelength adapting field. An appropriate name for this phenomenon is the "Sloan notch", after Louise Sloan, who first observed a notch in a foveal threshold spectrum. We have examined suprathreshold discriminability on both sides of the Sloan notch produced by a 6700 td, 578 nm adapting field. In a temporal two-alternative forced-choice paradigm, a suprathreshold 650 nm low-frequency "standard" stimulus was paired with low-frequency "test" stimuli, of wavelength between 600 and 670 nm and varied intensity; the observer's task was to identify the interval containing the standard. Discriminability of the test and standard typically dropped to chance for some particular test intensity, producing "indiscriminability action spectra", up to 0.7 log units above threshold. Truncated spectra (between about 530 and 560 nm) were also obtained from observers on the middle wavelength side of the Sloan notch, for a 550 nm standard. The indiscriminability action spectra of each observer were identical, up to scaling, with the observer's threshold action spectrum. Analysis of the action spectra shows that the indiscriminable stimuli are rendered equivalent at the input to a neural pathway where L- and M-cone signals converge with opposite sign. We also investigated discriminability in the spectral region containing and immediately surrounding the Sloan notch. Suprathreshold stimuli in the spectral region near the notch produce percepts that are always discriminable from 650 and 550 nm standards (and from one another), and thus we conclude that in this spectral region, perception is mediated in part by a pathway distinct from that which signals the standards. The action spectrum of this latter pathway was estimated with a variant of the discrimination procedure, and found similar to V lambda over the spectral region 575-610 nm.

Adaptation, Ocular↗

PubMed1996

Flicker sensitivity as a function of spectral density of external white temporal noise.

Foveal flicker sensitivity at 0.5-30 Hz was measured as a function of the spectral density of external, white, purely temporal noise for a sharp-edged 2.5 deg circular spot (mean luminance 3.4 log phot td). Sensitivity at any given temporal frequency was constant at low powers of external noise, but then decreased in inverse proportion to the square root of noise spectral density. Without external noise, sensitivity as function of temporal frequency had the well-known band-pass characteristics peaking at about 10 Hz, as previously documented in a large number of studies. In the presence of strong external noise, however, sensitivity was a monotonically decreasing function of temporal frequency. Our data are well described (goodness of fit 90%) by a model comprising (i) low-pass filtering by retinal cones, (ii) high-pass filtering in the subsequent neural pathways, (iii) adding of the temporal equivalent of internal white spatiotemporal noise, and (iv) detection by a temporal matched filter, the efficiency of which decreases approximately as the power -0.58 of temporal frequency.

Adult↗