Behavioral evaluation of auditory stream segregation in rats

Translational validity of neuropsychological tasks of sustained attention between rodents and humans: A systematic review of three rodent tasks

Atypical sustained attention is a symptom in a number of neurological and psychological conditions. Investigations into its neural underpinnings are required for improved management and treatment. Rodents are useful in investigating the neurobiology underlying atypical sustained attention and several rodent tasks have been developed for use in touchscreen testing platforms that mimic methodology used in human clinical attention assessment. This systematic review was conducted to assess how translatable these rodent tasks are to equivalent clinical human tasks. Studies using the rodent Continuous Performance Task (rCPT), Sustained Attention Task (SAT), and 5-choice CPT (5C-CPT) were sought and screened. Included in the review were 138 studies, using the rCPT (n = 21), SAT (n = 90), and 5C-CPT (n = 27). Translatability between rodent and human studies was assessed based on (1) methodological similarity, (2) performance similarity, and (3) replication of results. The 5C-CPT was found to be the most translatable cross-species paradigm with good utility, while the rCPT and SAT require adaptation and further development to meet these translatability benchmarks. With greater replication and more consistent results, greater confidence in the translation of sustained attention results between species will be engendered.

Neural correlates of novelty detection in the primary auditory cortex of behaving monkeys

The neural mechanisms underlying novelty detection are not well understood, especially in relation to behavior. Here, we present single-unit responses from the primary auditory cortex (A1) from two monkeys trained to detect deviant tones amid repetitive ones. Results show that monkeys can detect deviant sounds, and there is a strong correlation between late neuronal responses (250-350 ms after deviant onset) and the monkeys' perceptual decisions. The magnitude and timing of both neuronal and behavioral responses are increased by larger frequency differences between the deviant and standard tones and by increasing the number of standard tones preceding the deviant. This suggests that A1 neurons encode novelty detection in behaving monkeys, influenced by stimulus relevance and expectations. This study provides evidence supporting aspects of predictive coding in the sensory cortex.

Hearing in Complex Environments: Auditory Gain Control, Attention, and Hearing Loss

Listening in noisy or complex sound environments is difficult for individuals with normal hearing and can be a debilitating impairment for those with hearing loss. Extracting meaningful information from a complex acoustic environment requires the ability to accurately encode specific sound features under highly variable listening conditions and segregate distinct sound streams from multiple overlapping sources. The auditory system employs a variety of mechanisms to achieve this auditory scene analysis. First, neurons across levels of the auditory system exhibit compensatory adaptations to their gain and dynamic range in response to prevailing sound stimulus statistics in the environment. These adaptations allow for robust representations of sound features that are to a large degree invariant to the level of background noise. Second, listeners can selectively attend to a desired sound target in an environment with multiple sound sources. This selective auditory attention is another form of sensory gain control, enhancing the representation of an attended sound source while suppressing responses to unattended sounds. This review will examine both “bottom-up” gain alterations in response to changes in environmental sound statistics as well as “top-down” mechanisms that allow for selective extraction of specific sound features in a complex auditory scene. Finally, we will discuss how hearing loss interacts with these gain control mechanisms, and the adaptive and/or maladaptive perceptual consequences of this plasticity.