Fear Incubation Using an Extended Fear-Conditioning Protocol for Rats

Emotional memory has been primarily studied with fear-conditioning paradigms. Fear conditioning is a form of learning through which individuals learn the relationships between aversive events and otherwise neutral stimuli. The most-widely utilized procedures for studying emotional memories entail fear conditioning in rats. In these tasks, the unconditioned stimulus (US) is a footshock presented once or several times across single or several sessions, and the conditioned response (CR) is freezing. In a version of these procedures, called cued fear conditioning, a tone (conditioned stimulus, CS) is paired with footshocks (US) during the training phase. During the first test, animals are exposed to the same context in which training took place, and freezing responses are tested in the absence of footshocks and tones (i.e., a context test). During the second test, freezing is measured when the context is changed (e.g., by manipulating the smell and walls of the experimental chamber) and the tone is presented in the absence of footshocks (i.e., a cue test). Most cued fear conditioning procedures entail few tone-shock pairings (e.g., 1-3 trials in a single session). There is a growing interest in less common versions involving an extensive number of pairings (i.e., overtraining) related to the long-lasting effect called fear incubation (i.e., fear responses increase over time without further exposure to aversive events or conditioned stimuli). Extended fear-conditioning tasks have been key to the understanding of fear incubation's behavioral and neurobiological aspects, including its relationship with other psychological phenomena (e.g., post-traumatic stress disorder). Here, we describe an extended fear-conditioning protocol that produces overtraining and fear incubation in rats. This protocol entails a single training session with 25 tone-shock pairings (i.e., overtraining) and a comparison of conditioned freezing responses during context and cue tests 48 h (short-term) and 6 weeks (long-term) after training.

"Swimming against the current": Behavioral data of B etta splendens during an escape and avoidance task with water flows as the aversive stimulus

This paper describes the behavioral data of an experiment in which water flows (WFs) were first used as replacement of the traditional electric shocks to test free-operant avoidance in Betta splendens (Hurtado-Parrado et al. 2019 https://doi.org/10.1016/j.beproc.2018.10.021). WFs with a duration of 10 s each were delivered with 30-s flow-flow (F–F) and response-flow (R–F) intervals in a custom-made shuttle tank. Fish escaped or avoided the WFs by changing compartments. Crossings during the WFs, interrupted the flows, were automatically scored as escape (Esc), and initiated a new R–F interval. Crossings that occurred during R–F or F–F intervals were scored as avoidance responses and also reset the R–F interval. We compared the effect of adding a warning stimulus - curtains of air bubbles - to the last 5 s of the R–F interval; i.e., signaled versus unsignaled avoidance. A unique development of the WFs procedure, and thus the data here described, is that crossings were further differentiated into subcategories; namely, early avoidance (EA) if a crossing occurred during the first 25 s of the R–F interval; late avoidance (LA) if a crossing occurred during the last 5 s of the R–F interval; and Flow-Flow avoidance (FF) if a crossing occurred anytime during the F–F interval. Here we present the data of six bettas across the different phases of the experiment; namely, baseline (BL - no WFs programmed), signaled avoidance (SA – warning stimulus scheduled), and unsignaled avoidance (UA - no warning stimulus scheduled). The dataset available at the Open Science Framework (OSF) repository (http://doi.org/10.17605/OSF.IO/FMHXD (Hurtado-Parrado et al., 2019)) includes for each fish and per 20-min daily session the total number of crossings; frequency of each type of crossing (Esc, EA, LA, FF); total WF frequency and duration, the total time spent in each compartment, and an index of preference for each compartment based on the proportion of time spent in the tank's compartments.

Aversive control of Betta splendens behavior using water disturbances: Effects of signaled and unsignaled free-operant avoidance and escape contingencies

The vast majority of research on aversive control of behavior using animal models employs electric-shock based procedures with avian and mammalian species. Notwithstanding that pragmatic aspects explain this prominence in the field, there is still a need for testing well-established facts about shock-based aversive control using other, perhaps more ecologically valid or biologically relevant, forms of stimulation with other species. Following up on an observation that water disturbances appear to be aversive to Betta splendens (bettas), we developed a preparation for studying free-operant avoidance with this species in which water flows (WFs) replaced electric shocks. Fish changed compartments in a shuttle tank to escape or avoid 10-s WFs, which were delivered with 30-s flow-flow and response-flow intervals. We tested the effect of adding a warning stimulus (curtains of air bubbles) to the last 5 s of the response-flow interval (i.e., signaled avoidance) on the bettas' temporal distribution of crossings and swimming patterns. Escape was the predominant response, which importantly reduced the exposure to the WFs. Avoidance responses rarely exceeded the frequency of escape. The warning stimulus did not produce the expected postponement of responses to the last segment of the response-flow interval. Distinctive swimming patterns emerged, dissipated, and reappeared during baseline and treatment conditions. These findings confirm the aversive function of WFs for bettas and expand the generality of negative reinforcement phenomena using non-shock-based procedures with a less-frequently studied species. Further developments of the WFs paradigm show promise for replicating other aversive control phenomena (e.g., punishment), and analyzing spatiotemporal patterns produced by aversive contingencies.