Conditioned responses to time of hypothalamic neurons. The ventromedial nucleus]

Conditioned reactions to the time of regularly (every 30 sec.) presented pairings of an acoustic and an electrical cutaneous stimuli were studied in neurones of the hypothalamic ventromedial nucleus in an alert rabbit. Conditioned reactions of an inhibitory (81%) and activating (19%) types were elaborated in 27 out of 63 units (43%). They were significantly reproduced at six to nine omissions of stimulations at the stage of the 50th to 70th pairings. The maximum manifestation of trace processes coincides with the initial formation of a vegetative (electrocardiogram) component of the behavioral conditioned reflex to time. Significant correlation has been shown between the frequency of spikes in the pairings and their omissions, and the corresponding changes in heart rate at the same temporal intervals. This testifies to the involvement of the ventromedial nucleus structures in the formation of the vegetative component of the behavioral conditioned reflex to time. Common characteristics and peculiarities of conditioned reactions to time have been revealed in units of the hypothalamic ventromedial and perifornical nuclei in accordance with morpho-functional properties of the examined structures.     

Conditioned reactions to time of hypothalamic neurons. The perifornical nucleus]

In 40% of the 52 neurones of the hypothalamic perifornical nucleus in alert rabbits conditioned trace reactions of the activational (52%) and inhibitory (48%) type were recorded in the course of elaboration of a conditioned motor reflex to time. The sign and pattern of the trace responses were determined by the nature of cell reactions to actual paired stimuli. After 50 to 70 pairings, the unit trace conditioned reaction to time persisted for a period of 10 to 15 successive omissions. Trace responses were observed most frequently in the 5th of 8th omissions. In some cases conditioned enhancement of cell activity coincided with the conditioned motor response to time. This fact together with the maximal development of a summery trace cellular response at the moment of formation of conditioned motor reactions attests the participation of neurones of the perifornical nucleus in maintaining conditioned motor activity.     

Distributions of time to fixation of neutral genes

Exact distributions of times to fixation are derived for neutral alleles in a discrete generation, constant census model that accommodates specified variations in gametic contributions per parent. This enables an evaluation of the performance of the effective number concept, and of diffusion equation approximations, used to characterize the time scale of drift events. Following simultaneous comparisons of modes, medians, means and standard deviations of exact and approximate distributions of times to fixation, it is concluded that diffusion equation methods, in conjunction with the appropriate effective number, do produce accurate results.     

Factors related to the time of fixation of the conceptus in mares

The temporal relationships among day of conceptus fixation (cessation of mobility), conceptus diameter, uterine tone, uterine contractility, and myometrial and endometrial thickness of the middle and caudal segments of the uterine horns were assessed in 13 pony mares with fixation in the caudal segment of a uterine horn. The mean day of fixation (14.9 +/- 0.3) was established by 2-h mobility trials. Uterine tone increased (P < 0.0001) gradually over Days 11 to 21, whereas uterine contractility decreased (P < 0.0001) between Days 14 and 18. The diameter of the spherical embryonic vesicle increased (P < 0.0001) between Days 11 and 17. The day of fixation and vesicle diameter on Day 14 were negatively correlated (r = -0.9, P < 0.007); the larger the vesicle, the earlier fixation occurred. Each of 4 uterine-horn diameters (endometrium and endometrium plus myometrium of middle and caudal segments) decreased (P < 0.0001) correspondingly over Days 11 to 21. On the day of fixation conceptus diameter (21.5 +/- 1.0 mm) was similar to endometrial diameter (21.1 +/- 0.4 mm) at the caudal segment. The endometrial diameter represents the distance between the inner opposite walls of the myometrium. The percentage of change between the day before and day of fixation was greater for the conceptus (18.1% increase) than for the endometrial diameter at the caudal segment (1.0% decrease). The results suggest that fixation occurred when the mobile and growing conceptus attained, on the average, a diameter equivalent to the distance between opposite inner myometrial walls at the caudal segment. The uterus became turgid by this time and presumably did not expand adequately to accommodate continued mobility of the expanding conceptus.     

Genetic drift on networks: Ploidy and the time to fixation

Genetic drift in finite populations ultimately leads to the loss of genetic variation. This paper examines the rate of neutral gene loss for a range of population structures defined by a graph. We show that, where individuals reside at fixed points on an undirected graph with equal degree nodes, the mean time to loss differs from the panmictic value by a positive additive term that depends on the number of individuals (not genes) in the population. The effect of these spatial structures is to slow the time to fixation by an amount that depends on the way individuals are distributed, rather than changing the apparent number of genes available to be sampled. This relationship breaks down, however, for a broad class of spatial structures such as random, small-world and scale-free networks. For the latter structures there is a counter-intuitive acceleration of fixation proportional to the level of ploidy.     

Genetic drift on networks: ploidy and the time to fixation

Genetic drift in finite populations ultimately leads to the loss of genetic variation. This paper examines the rate of neutral gene loss for a range of population structures defined by a graph. We show that, where individuals reside at fixed points on an undirected graph with equal degree nodes, the mean time to loss differs from the panmictic value by a positive additive term that depends on the number of individuals (not genes) in the population. The effect of these spatial structures is to slow the time to fixation by an amount that depends on the way individuals are distributed, rather than changing the apparent number of genes available to be sampled. This relationship breaks down, however, for a broad class of spatial structures such as random, small-world and scale-free networks. For the latter structures there is a counter-intuitive acceleration of fixation proportional to the level of ploidy.     

Conditioned responding to magnetic fields by honeybees

Summary Individual honeybees were trained in two experiments to come for sucrose solution to a target set on a shelf before an open laboratory window. On some visits, the target was presented in the ambient geomagnetic field, and on other visits in a field modified in the vicinity of the target by passing a direct current through a coil under the shelf. The target contained 50% sucrose when it was in one of the two fields and 20% sucrose when it was in the other. Tested subsequently with a pair of targets, one in the ambient field, one in the modified field, and both containing tap water, the animals significantly preferred the target in the field in which they had been given the 50% sucrose during training. Four modified fields, produced with different coils and currents, were discriminated equally well from the ambient field, and performance was as good when the 50% sucrose was given in the ambient field as when it was given in the modified field. Data are provided also to illustrate the excellent discriminative performance attainable when two targets are presented on each training visit — one in a modified field, the other in the ambient field — and choice of one is rewarded with 50% sucrose while choice of the other is punished with mild electric shock. Our results show that foragers attend to magnetic stimuli at the feeding site and that discriminative training techniques are appropriate for the study of magnetoreception and its mechanism in honeybees.     

Updating versus Exposure to Prevent Consolidation of Conditioned Fear

Targeting the consolidation of fear memories following trauma may offer a promising method for preventing the development of flashbacks and other unwanted re-experiencing symptoms that characterise Posttraumatic Stress Disorder (PTSD). Research has demonstrated that performing visuo-spatial tasks after analogue trauma can block the consolidation of fear memory and reduce the frequency of flashbacks. However, no research has yet used verbal techniques to alter memories during the consolidation window. This is surprising given that the most effective treatments for PTSD are verbally-based with exposure therapy and trauma-focused cognitive behavioural therapy gaining the most evidence of efficacy. Psychological therapies aim to reduce the conditioned fear response, which is in keeping with the preliminary finding that an increased propensity for fear conditioning may be a vulnerability factor for PTSD. Our research had two aims. We investigated the degree to which individual differences in fear conditioning predict the development of PTSD symptoms. We also compared the preventative effects of two clinically informed psychological techniques administered during the consolidation window: exposure to the trauma memory and updating the meaning of the trauma. 115 healthy participants underwent a fear conditioning paradigm in which traumatic film stimuli (unconditioned stimuli) were paired with neutral stimuli (conditioned stimuli). Participants were randomly allocated to an updating, exposure or control group to compare the effects on the conditioned fear response and on PTSD symptomatology. The results showed that stronger conditioned responses at acquisition significantly predicted the development of PTSD symptoms. The updating group, who verbally devalued the unconditioned stimulus within the consolidation window, experienced significantly lower levels of PTSD symptoms during follow-up than the exposure and control groups. These findings are consistent with clinical interventions for chronic PTSD and have important implications for identifying those at risk as well as for designing novel early interventions to prevent the development of PTSD.     

Conditioned gonadal response of Japanese quail to cyclic photoperiod

The conditioning effect of cyclic photoperiods was studied in 9 experiments. Quail after 1 day of age were exposed to repeated cycles of 6 hr of light and 18 hr of darkness during their first 4 weeks.Afterwards the groups were established to study the effect of (a) ahemeral (unnatural daylength); (b) phase shifted, and (c) abbreviated photoperiods. The quail were kept on such regimens for 3 weeks. The results based on the 7-week testicular weights indicated that quail did not respond to a phase shift in the light period but responded to an abbreviation of a previously established photoperiod.Quail responded to unnatural daylength even when the actual and relative length of the dark period increased.

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Zusammenfassung Die konditionierende Wirkung von zyklischen Photoperioden wurde in 9 Experimenten untersucht. Japanische Wachteln wurden nach der Geburt 4 Wochen einem Zyklus von 6L:18D Studen exponiert.Anschliessend wurden die Tiere in Gruppen eingeteilt, um die Wirkung von: (a) unnatürlicher Tageslänge; (b) Phasenwechsel, und (c) verkürzten Photoperioden bei 3 Wochen Exponierung zu prüfen.Die Ergebnisse beziehen sich auf das Hodengewicht nach 7 Wochen. Danach reagierten die Wachteln nicht auf einen Phasenwechsel in der Lichtperiode,wohl aber auf eine Verkürzung der bis dahin bestandenen Photoperiode.Wachteln reagierten auf unnatürliche Tageslänge auch dann, wenn die wirkliche und relative Länge der Dunkelperiode zunahm.

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Resume L'effet de mise en condition qu'ont des périodes cycliques de lumière a été étudié au cours de neuf essais. Des cailles japonaises ont été soumises dès le lendemain de leur éclosion et durant 4 semaines à un régime de 6 heures de lumière suivies de 18 heures d'obscurité. Ensuite, les oiseaux furent placés durant 3 semaines en groupe afin d'étudier l'effet: (a) d'une durée du jour non-naturelle;(b)du changement de phase et (c) d'une période d'éclairement très brève. Les répercussions de ces anomalies sont chiffrées au moyen du poids des testicules après 7 semaines.Selon ce critère, les cailles ne réagissent pas à un changement de phase dans la période de lumière, mais bien à un racourcissement de la durée d'éclairement par rapport à la période précédente. Les cailles ont aussi réagi à une longueur non-naturelle du jour, mais uniquement si la durée d'obscurité réelle et relative augmentait.

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Presented at the 4th International Biometeorological Congress,New Brunswick, New Jersey, 26 August – 2 September 1966. This investigation was supported in part by USDA Regional Research Project W-50.