The Strength of the Medial Olivocochlear Reflex in Chinchillas Is Associated With Delayed Response Performance in a Visual Discrimination Task With Vocalizations as Distractors

The ability to perceive the world is not merely a passive process but depends on sensorimotor loops and interactions that guide and actively bias our sensory systems. Understanding which and how cognitive processes participate in this active sensing is still an open question. In this context, the auditory system presents itself as an attractive model for this purpose as it features an efferent control network that projects from the cortex to subcortical nuclei and even to the sensory epithelium itself. This efferent system can regulate the cochlear amplifier sensitivity through medial olivocochlear (MOC) neurons located in the brainstem. The ability to suppress irrelevant sounds during selective attention to visual stimuli is one of the functions that have been attributed to this system. MOC neurons are also directly activated by sounds through a brainstem reflex circuit, a response linked to the ability to suppress auditory stimuli during visual attention. Human studies have suggested that MOC neurons are also recruited by other cognitive functions, such as working memory and predictability. The aim of this research was to explore whether cognitive processes related to delayed responses in a visual discrimination task were associated with MOC function. In this behavioral condition, chinchillas held their responses for more than 2.5 s after visual stimulus offset, with and without auditory distractors, and the accuracy of these responses was correlated with the magnitude of the MOC reflex. We found that the animals’ performance decreased in presence of auditory distractors and that the results observed in MOC reflex could predict this performance. The individual MOC strength correlated with behavioral performance during delayed responses with auditory distractors, but not without them. These results in chinchillas, suggest that MOC neurons are also recruited by other cognitive functions, such as working memory.

Gut microbiome drives individual memory variation in bumblebees

The potential of the gut microbiome as a driver of individual cognitive differences in natural populations of animals remains unexplored. Here, using metagenomic sequencing of individual bumblebee hindguts, we find a positive correlation between the abundance of Lactobacillus Firm-5 cluster and memory retention on a visual discrimination task. Supplementation with the Firm-5 species Lactobacillus apis, but not other non-Firm-5 bacterial species, enhances bees’ memory. Untargeted metabolomics after L. apis supplementation show increased LPA (14:0) glycerophospholipid in the haemolymph. Oral administration of the LPA increases long-term memory significantly. Based on our findings and metagenomic/metabolomic analyses, we propose a molecular pathway for this gut-brain interaction. Our results provide insights into proximate and ultimate causes of cognitive differences in natural bumblebee populations.

Overtraining Strengthens the Visual Discrimination Memory Trace Outside the Hippocampus in Male Rats

The hippocampus (HPC) may compete with other memory systems when establishing a representation, a process termed overshadowing. However, this overshadowing may be mitigated by repeated learning episodes, making a memory resistant to post-training hippocampal damage. In the current study, we examined this overshadowing process for a hippocampal-dependent visual discrimination memory in rats. In Experiment 1, male rats were trained to criterion (80% accuracy on two consecutive days) on a visual discrimination and then given 50 additional trials distributed over 5 days or 10 weeks. Regardless of this additional learning, extensive damage to the HPC caused retrograde amnesia for the visual discrimination, suggesting that the memory remained hippocampal-dependent. In Experiment 2, rats received hippocampal damage before learning and required approximately twice as many trials to acquire the visual discrimination as control rats, suggesting that, when the overshadowing or competition is removed, the non-hippocampal memory systems only slowly acquires the discrimination. In Experiment 3, increasing the additional learning beyond criterion by 230 trials, the amount needed in Experiment 2 to train the non-hippocampal systems in absence of competition, successfully prevented the retrograde amnesic effects of post-training hippocampal damage. Combined, the findings suggest that a visual discrimination memory trace can be strengthened in non-hippocampal systems with overtraining and become independent of the HPC.

Acquisition of a Learned Operant and Critical Flicker-Fusion Rate in the Tuatara (Sphenodon spp.)

<p>Scientific investigation of the sensory world and behavior of the tuatara is limited. This study incorporates both ecological and psychological perspectives to test learning and visual perception using a novel operant technique and flicker-fusion rates to measure visual discrimination in tuatara. We posed four main questions: (1) can a reliable method examine learning and visual perception in tuatara?, (2) what is the critical flicker-fusion (CFF) rates for tuatara and how does it relate to motion detection ability?, (3) can stimulus control be transferred to a Y-maze from an open field arena?, and (4) what are the implications for behavioral ecology, conservation, and species welfare? Tuatara (Sphenodon punctatus) were trained using an operant conditioning procedure with food reinforcement to respond to discriminative stimuli (S+) of various flicker-fusion rates, and ignore a non-discriminative stimulus (S-). Tuatara discriminated CFF rates between 2.65-45.61 Hz, but not at 65.09 Hz. The upper threshold between 45.61-65.09 Hz is comparable to other mammalian, avian, and herpetological species. Tuatara demonstrated a learning capacity for acquisition of an operant task as well as cognitive development for learning and memory strategies. Visual discrimination is important to tuatara and may facilitate behavioral responses to many context-dependent ecological processes (i.e., predator/prey/kin recognition, mate selection, environmental discrimination, optimal foraging strategies, and communication). By understanding the importance of visual stimuli, the study provides a better perspective of the tuatara natural sensory world. Additionally, a reliable method was established that can be used for more comprehensive psychophysical experiments to further access visual perception and learning in all reptiles, with the potential to examine other sensory mechanisms such as audition, chemoreception, and tactility.</p>

Acquisition of a Learned Operant and Critical Flicker-Fusion Rate in the Tuatara (Sphenodon spp.)

<p>Scientific investigation of the sensory world and behavior of the tuatara is limited. This study incorporates both ecological and psychological perspectives to test learning and visual perception using a novel operant technique and flicker-fusion rates to measure visual discrimination in tuatara. We posed four main questions: (1) can a reliable method examine learning and visual perception in tuatara?, (2) what is the critical flicker-fusion (CFF) rates for tuatara and how does it relate to motion detection ability?, (3) can stimulus control be transferred to a Y-maze from an open field arena?, and (4) what are the implications for behavioral ecology, conservation, and species welfare? Tuatara (Sphenodon punctatus) were trained using an operant conditioning procedure with food reinforcement to respond to discriminative stimuli (S+) of various flicker-fusion rates, and ignore a non-discriminative stimulus (S-). Tuatara discriminated CFF rates between 2.65-45.61 Hz, but not at 65.09 Hz. The upper threshold between 45.61-65.09 Hz is comparable to other mammalian, avian, and herpetological species. Tuatara demonstrated a learning capacity for acquisition of an operant task as well as cognitive development for learning and memory strategies. Visual discrimination is important to tuatara and may facilitate behavioral responses to many context-dependent ecological processes (i.e., predator/prey/kin recognition, mate selection, environmental discrimination, optimal foraging strategies, and communication). By understanding the importance of visual stimuli, the study provides a better perspective of the tuatara natural sensory world. Additionally, a reliable method was established that can be used for more comprehensive psychophysical experiments to further access visual perception and learning in all reptiles, with the potential to examine other sensory mechanisms such as audition, chemoreception, and tactility.</p>