"Thinking like a Neuroscientist": Using Scaffolded Grant Proposals to Foster Scientific Thinking in a Freshman Neuroscience Course.

Learning and practicing scientific inquiry is an essential component of a STEM education, but it is often difficult to teach to novices or those outside of a laboratory setting. To promote scientific thinking in a freshmen introductory neuroscience course without a lab component, we developed a series of learning activities and assignments designed to foster scientific thinking through the use of scientific grant proposals. Students wrote three short grant proposals on topics ranging from molecular to cognitive neuroscience during a 10-week class (one quarter). We made this challenging and advanced task feasible for novice learners through extensive instructional scaffolding, opportunity for practice, and frequent peer and instructor feedback. Student and instructor reports indicate that the assignments were highly intellectually engaging and that they promoted critical thinking, a deeper understanding of neuroscience material, and effective written communication skills. Here we outline the mechanics of the assignment, student and instructor impressions of learning outcomes, and the advantages and disadvantages of implementing this approach.

Perceptual and neuronal boundary learned from higher-order stimulus probabilities.

During an early epoch of development, the brain is highly adaptive to the stimulus environment. Exposing young animals to a particular tone, for example, leads to an enlarged representation of that tone in primary auditory cortex. While the neural effects of simple tonal environments are well characterized, the principles that guide plasticity in more complex acoustic environments remain unclear. In addition, very little is known about the perceptual consequences of early experience-induced plasticity. To address these questions, we reared juvenile rats in complex multitone environments that differed in terms of the higher-order conditional probabilities between sounds. We found that the development of primary cortical acoustic representations, as well as frequency discrimination ability in adult animals, were shaped by the higher-order stimulus statistics of the early acoustic environment. Our results suggest that early experience-dependent cortical reorganization may mediate perceptual changes through statistical learning of the sensory input.

Cortical plasticity as a mechanism for storing Bayesian priors in sensory perception.

Human perception of ambiguous sensory signals is biased by prior experiences. It is not known how such prior information is encoded, retrieved and combined with sensory information by neurons. Previous authors have suggested dynamic encoding mechanisms for prior information, whereby top-down modulation of firing patterns on a trial-by-trial basis creates short-term representations of priors. Although such a mechanism may well account for perceptual bias arising in the short-term, it does not account for the often irreversible and robust changes in perception that result from long-term, developmental experience. Based on the finding that more frequently experienced stimuli gain greater representations in sensory cortices during development, we reasoned that prior information could be stored in the size of cortical sensory representations. For the case of auditory perception, we use a computational model to show that prior information about sound frequency distributions may be stored in the size of primary auditory cortex frequency representations, read-out by elevated baseline activity in all neurons and combined with sensory-evoked activity to generate a perception that conforms to Bayesian integration theory. Our results suggest an alternative neural mechanism for experience-induced long-term perceptual bias in the context of auditory perception. They make the testable prediction that the extent of such perceptual prior bias is modulated by both the degree of cortical reorganization and the magnitude of spontaneous activity in primary auditory cortex. Given that cortical over-representation of frequently experienced stimuli, as well as perceptual bias towards such stimuli is a common phenomenon across sensory modalities, our model may generalize to sensory perception, rather than being specific to auditory perception.

Feature-dependent sensitive periods in the development of complex sound representation.

Simple tonal stimuli can shape spectral tuning of cortical neurons during an early epoch of brain development. The effects of complex sound experience on cortical development remain to be determined. We exposed rat pups to a frequency-modulated (FM) sweep in different time windows during early development, and examined the effects of such sensory experience on sound representations in the primary auditory cortex (AI). We found that early exposure to a FM sound resulted in altered characteristic frequency representations and broadened spectral tuning in AI neurons, whereas later exposure to the same sound only led to greater selectivity for the sweep rate and direction of the experienced FM sound. These results indicate that cortical representations of different acoustic features are shaped by complex sounds in a series of distinct sensitive periods.

Early experience impairs perceptual discrimination.

Sensory experience can reorganize cortical sensory representations in an epoch of early development. During this period, cortical sensory neurons may shift their response selectivity and become tuned to more frequently occurring stimuli. Although this enlarged cortical representation is believed to underlie improved sensory processing of the experienced stimuli, its precise perceptual consequences are still unknown. We show that rearing rats in a single-frequency tonal environment results in enlarged cortical representations of the frequencies near that of the experienced tone, but the animals are impaired in perceptual discrimination of the over-represented frequencies. By contrast, discrimination of the neighboring under-represented frequencies is substantially improved. Computational analysis indicated that the altered perceptual ability could be fully accounted for by the sound exposure-induced reorganization of cortical primary auditory representations. These results indicate that early experience shapes sensory perception. The same plasticity processes may be important in optimizing phonemic representations in humans.