Social transmission of Pavlovian fear: fear-conditioning by-proxy in related female rats

Pairing a previously neutral conditioned stimulus (CS; e.g., a tone) to an aversive unconditioned stimulus (US; e.g., a foot-shock) leads to associative learning such that the tone alone will elicit a conditioned response (e.g., freezing). Individuals can also acquire fear from a social context, such as through observing the fear expression of a conspecific. In the current study, we examined the influence of kinship/familiarity on social transmission of fear in female rats. Rats were housed in triads with either sisters or non-related females. One rat from each cage was fear conditioned to a tone CS+ shock US. On day two, the conditioned rat was returned to the chamber accompanied by one of her cage mates. Both rats were allowed to behave freely, while the tone was played in the absence of the foot-shock. The previously untrained rat is referred to as the fear-conditioned by-proxy (FCbP) animal, as she would freeze based on observations of her cage-mate’s response rather than due to direct personal experience with the foot-shock. The third rat served as a cage-mate control. The third day, long-term memory tests to the CS were performed. Consistent with our previous application of this paradigm in male rats (Bruchey et al. in Behav Brain Res 214(1):80–84, 2010), our results revealed that social interactions between the fear conditioned and FCbP rats on day two contribute to freezing displayed by the FCbP rats on day three. In this experiment, prosocial behavior occurring at the termination of the cue on day two was significantly greater between sisters than their non-sister counterparts, and this behavior resulted in increased freezing on day three. Our results suggest that familiarity and/or kinship influences the social transmission of fear in female rats.     

Teachers With Linguistically Informed Knowledge of Reading Subskills are Associated with a Matthew Effect in Reading Comprehension for Monolingual and Bilingual Students

A longitudinal investigation determined the growth of reading comprehension from third to fifth grades in a cohort of students who received Language Enrichment (LE), an Orton-Gillingham–based literacy program, during first and second grades. The LE instruction was provided by regular education teachers who received comprehensive training in linguistically informed content pertaining to reading subskills. All students were traditionally instructed in kindergarten, third, fourth, and fifth grades. Hierarchical linear modeling (HLM) confirmed that mono- and bilingual students had significantly advantaged individual growth in reading comprehension as measured on the state-mandated Texas Assessment of Academic Skills (TAAS) when their teachers had more experience implementing LE over students whose teachers had less experience implementing LE, or students whose teachers had no LE training. Findings showed a fan-shaped spread in achievement from third to fifth grades for all students in the cohort. The significance of the spread was confirmed by reliable covariance between the initial reading level and the growth in reading across grade levels. This fan-shaped growth pattern is often referred to as a Matthew effect in reading comprehension (Stanovich, 1986 Stanovich, K. E. 1986. Matthew effects in reading: Some consequences of individual differences in the acquisition of literacy. Reading Research Quarterly, 21(4): 360–407. [Crossref], [Web of Science ®] , [Google Scholar]). These results provide evidence that the Matthew effect may be associated with specific teaching pedagogies, especially early direct implementation of multisensory linguistically informed language arts instruction. LE instruction emphasizes phonemic awareness, symbol–sound correspondences, morphology, and vocabulary to develop phonological decoding strategies, word recognition accuracy, and comprehension of words in text.     

Predictability and heritability of individual differences in fear learning

Our objective was to characterize individual differences in fear conditioning and extinction in an outbred rat strain, to test behavioral predictors of these individual differences, and to assess their heritability. We fear-conditioned 100 Long-Evans rats, attempted to extinguish fear the next day, and tested extinction recall on the third day. The distribution of freezing scores after fear conditioning was skewed, with most rats showing substantial freezing; after fear extinction, the distribution was bimodal with most rats showing minimal freezing, but a substantial portion showing maximal freezing. Longer rearing episodes measured prior to conditioning predicted less freezing at the beginning of extinction, but differences in extinction learning were not predicted by any baseline exploratory behaviors. We tested the heritability of extinction differences by breeding rats from the top and bottom 20 % of freezing scores during extinction recall. We then ran the offspring through the same conditioning/extinction procedure, with the addition of recording ultrasonic vocalizations throughout training and testing. Only a minority of rats emitted distress vocalizations during fear acquisition, but the incidence was less frequent in the offspring of good extinguishers than in poor extinguishers or randomly bred controls. The occurrence of distress vocalizations during acquisition predicted higher levels of freezing during fear recall regardless of breeding line, but the relationship between vocalization and freezing was no longer evident following extinction training, at which point freezing levels were influenced only by breeding and not by vocalization. The heritability (h ²) of extinction recall was estimated at 0.36, consistent with human estimates.     

Motor maps, seizures, and behaviour

Atypically organised motor maps have been described in some people with epilepsy and we have modelled this in rats. Our goal is to more fully understand the mechanisms responsible for seizure-induced functional brain reorganisation and to reverse their effects. Here we present an overview of the relationship between neocortical motor maps, seizures, and interictal behaviour. To begin we summarise the observations of atypical motor maps with epilepsy and in animal models following experimentally induced seizures. Our novel experiments have established that motor map expansion is linked to a functional alteration of motor behaviour. Evidence for some of the putative brain mechanisms responsible for motor map size is discussed. Our successes reversing seizure-induced map expansion by two different methods are also briefly reviewed. Lastly, unanswered questions for possible future experimentation are posed.     

Dominance status predicts social fear transmission in laboratory rats

Acquiring information about stimuli that predict danger, through either direct experience or inference from a social context, is crucial for individuals’ ability to generate appropriate behaviors in response to threats. Utilizing a modified demonstrator–observer paradigm (fear conditioning by proxy) that allows for free interaction between subjects, we show that social dominance hierarchy, and the interactive social behaviors of caged rats, is predictive of social fear transmission, with subordinate rats displaying increased fear responses after interacting with a fear-conditioned dominant rat during fear retrieval. Fear conditioning by proxy conserves some of the pathways necessary for direct fear learning (e.g., lateral amygdala) but is unique in that it requires regions necessary for emotional regulation (e.g., anterior cingulate cortex), making this paradigm an important tool for evaluating learning and behavior in the laboratory setting.     

Number-of-features effects and semantic processing

Participants list many semantic features for some concrete nouns (e.g., lion) and fewer for others (e.g., lime; McRae, de Sa, & Seidenberg, 1997). Pexman, Lupker, and Hino (2002) reported faster lexical decision and naming responses for high number of features (NOF) words than for low-NOF words. In the present research, we investigated the impact of NOF on semantic processing. We observed NOF effects in a self-paced reading task when prior context was not congruent with the target word (Experiment 1) and in a semantic categorization task (concrete vs. abstract; Experiment 2A). When we narrowed our stimuli to include high- and low-NOF words from a single category (birds), we found substantial NOF effects that were modulated by the specificity of the categorization task (Experiments 3A, 3B, and 3C). We argue that these results provide support for distributed representation of word meaning.     

Language Enrichment Teacher Preparation and Practice Predicts Third Grade Reading Comprehension

First and second grade public school teachers were trained through interactive video-conferencing to implement Language Enrichment, an Orton-Gillingham-based literacy instruction. The effectiveness of the linguistically informed training was demonstrated by documenting the longitudinal third grade reading comprehension achievement of their students. Student achievement was measured on the state-mandated achievement test, Texas Assessment of Academic Skills (TAAS). Hierarchical linear modeling (HLM) showed that students whose teachers were trained in Language Enrichment instruction had higher third grade reading comprehension achievement than students whose teachers were not trained. Additionally, a significant effect of the length of Language Enrichment teaching experience of the second grade teacher on third grade reading comprehension was found. Earlier occurring second grade teacher training was associated with higher reading scores than later training. Based on these findings it is suggested that teachers who have content-rich knowledge known to support literacy acquisition can provide reading instruction that results in a level of reading comprehension that is significantly higher than that resulting from teachers who do not have a well-developed domain of knowledge concerning the reading process. This study also indicates that teacher competence was enhanced through practice because student reading achievement of the more-experienced Language Enrichment teachers was higher than that of the less-experienced Language Enrichment teachers.