Analysis of Habituation Learning in Mealworm Pupae (Tenebrio molitor)

The decline of response as a consequence of repeated stimulation is known as habituation. The goal of the present experiments was extending the knowledge about habituation of abdominal contractions in the pupa of Tenebrio molitor. Both experiments consisted of two phases. During Phase 1, all groups were exposed to a continuous stimulus (light in Experiment 1 and vibration in Experiment 2). At the beginning of this phase, pupae showed a high number of abdominal contractions. However, during the last minute of Phase 1, the number of abdominal contractions was lower. In the next phase, the pupae were divided in different groups to test for response recovery. We found an increase in the abdominal contractions when subjects were exposed to a different stimulus, be it within the same or in a distinct sensory modality. In addition, we also reported response recovery when the pupae were re-exposed to the original stimuli after a resting period. Results indicate that the increase in responding cannot be explained by either sensory adaptation or fatigue. The findings are consistent with the perspective that suggests that habituation plays a major role in the survival of the species, even in non-feeding developmental stages.

A light way for nuclear cell biologists

The nucleus is a very complex organelle present in eukaryotic cells. Having the crucial task to safeguard, organize and manage the genetic information, it must tightly control its molecular constituents, its shape and its internal architecture at any given time. Despite our vast knowledge of nuclear cell biology, much is yet to be unraveled. For instance, only recently we came to appreciate the existence of a dynamic nuclear cytoskeleton made of actin filaments that regulates processes such as gene expression, DNA repair and nuclear expansion. This suggests further exciting discoveries ahead of us. Modern cell biologists embrace a new methodology relying on precise perturbations of cellular processes that require a reversible, highly spatially-confinable, rapid, inexpensive and tunable external stimulus: light. In this review, we discuss how optogenetics, the state-of-the-art technology that uses genetically-encoded light-sensitive proteins to steer biological processes, can be adopted to specifically investigate nuclear cell biology.

Top-down knowledge about reflection modulates response competition to multisensory stimuli

An image reflected in a mirror may appears in the visual field in a location opposite to the physical location of the object in the environment, in particular it may appear on the right when the object is on the left and vice versa. Through experience people have knowledge that reflections are not real objects an also that they are informative about object locations. We tested the importance of this knowledge in a simple task in which participants had to respond to a visual stimulus (light from an LED) that could appear in the right or left visual field. Participants had to respond with the contralateral hand, i.e., they had to press the right button if the light was on the left and vice versa. An irrelevant sound could also originate from the left or the right side. To avoid different bouncing of the sound the mirror condition was compared to a glass condition so that the solid surfaces were identical in size. When light and sound had the same spatial origin responses were faster, however this was only true as long as the light was seen though a glass and not seen reflected in a mirror. We conclude that participants are influenced by the knowledge about the origin of a light when when this information is irrelevant for their task.

Problems of Conditioning Xenopus Laevis Tadpoles with Standard Avoidance-Response Learning Paradigms

The amphibian Xenopus laevis embryo (tadpole) provides a satisfactory alternative to mammalian screening for structural teratogens. Testing was undertaken to extend the usefulness of this species for behavioral teratogenicity testing. One simple and eight operant conditioning paradigms were examined: none elicited learning in Xenopus embryos. Adaptation to the conditioning stimulus (light) and freezing in response to the unconditioned stimulus (shock) were responses incompatible with conditioned learning.

Reactivity in Extroverts and Introverts

The response times of 17 introverts and 24 extroverts to red and blue stimulus lights were compared. While no differences were found between the groups, introverts responded faster to the presentation of the red stimulus light than the blue one.

Spectral sensitivity of monocularly deprived cats

The reports of rod-dominated psychophysical spectral sensitivity from the deprived eye of monocularly lid-sutured (MD) monkeys are intriguing but difficult to reconcile with the absence of any reported deprivation effects in retina. As most studies of MD retina have been from cat, we have examined psychophysically the increment threshold spectral sensitivity of MD cats using both reaction time and simultaneous two-choice behavioral procedures. Although the deprived eyes exhibited an absolute increment threshold sensitivity deficit, both rod and cone spectral sensitivity functions were obtained on large white backgrounds. This normal transition from rod to cone vision, as background luminance increased, was also found in threshold vs. intensity functions. Using their deprived eye, some cats exhibited a rod spectral sensitivity function when a smaller, normally photopic, background was used providing some support for a hypothesis that the rod-dominated spectral sensitivity observed in monkey may represent detection of scattered stimulus light. Alternatively monocular deprivation may reveal a rod-dominated mechanism which exists in monkey but not in cat.

Blocking as a Retrieval Failure: Reactivation of Associations to a Blocked Stimulus

Conditioned lick suppression in rats was used to examine the effectiveness of three different “reminder” treatments in reactivating associations to a blocked stimulus in a Kamin blocking paradigm. Experiment I indicated that with our parameters prior tone-footshock pairings could block manifestation of a light-footshock association that would otherwise be evident following pairings of a light-tone compound stimulus with footshock. In Experiment II, exposure to either the US, the blocked stimulus (light), or the apparatus cues between the compound conditioning trials and testing decreased blocking. Experiments III(a) and III(b) replicated the unblocking effects seen in Experiment II and included control groups that received the identical training and reminder treatments except for the omission of the light from the compound stimulus. These latter animals failed to display behaviour comparable to the blocked and reminded subjects, thereby establishing the associative basis of suppression to the light in the animals reminded following treatment known to produce blocking. Experiment IV also replicated the results of Experiment II and included control groups that received identical light-tone compound trials and reminder treatments without prior conditioning to the tone alone. In these control groups, reminder treatments tended to disrupt rather than increase evidence of conditioning to the light. The results suggest that associations are formed to the added element of a compound despite prior conditioning to the initial element, and that failure on the test trial to retrieve these associations to the blocked CS, rather than a failure to attend to or learn about the added element, is at least in part responsible the Kamin blocking effect.

An Autokinetic Stimulus-Light Modification Providing Uniform Intensity at Wide Viewing Angles

A simple modification of the autokinetic-stimulus apparatus removes differences in Ss' judgments caused by unequal intensities of the stimulus due to differing viewing angles.

Directional Differences in the Colour Sensitivity of Daphnia Magna

1. The Daphnia compound eye movements can be driven by a flashing light. 2. The action spectrum for the threshold light intensity required to evoke this response depends on the orientation of the stimulus light beam with respect to the animal. 3. If the light falls on the eye through the top of the animal's head the action spectrum peaks at the low wavelength end of the spectrum, while if it falls on the eye through the side of the head the peak is in the yellow-green. 4. Eye movements cannot be evoked by illuminating any part of the animal except the compound eye so neither of these action spectra is due to a light receptor other than the compound eye. 5. Some anomalous action spectra in the literature on the behaviour of free-swimming Daphnia are accounted for.