Cortical Activation Patterns Evoked by Temporally Asymmetric Sounds and Their Modulation by Learning

How far neuroscience is from understanding brains

The cellular biology of brains is relatively well-understood, but neuroscientists have not yet generated a theory explaining how brains work. Explanations of how neurons collectively operate to produce what brains can do are tentative and incomplete. Without prior assumptions about the brain mechanisms, I attempt here to identify major obstacles to progress in neuroscientific understanding of brains and central nervous systems. Most of the obstacles to our understanding are conceptual. Neuroscience lacks concepts and models rooted in experimental results explaining how neurons interact at all scales. The cerebral cortex is thought to control awake activities, which contrasts with recent experimental results. There is ambiguity distinguishing task-related brain activities from spontaneous activities and organized intrinsic activities. Brains are regarded as driven by external and internal stimuli in contrast to their considerable autonomy. Experimental results are explained by sensory inputs, behavior, and psychological concepts. Time and space are regarded as mutually independent variables for spiking, post-synaptic events, and other measured variables, in contrast to experimental results. Dynamical systems theory and models describing evolution of variables with time as the independent variable are insufficient to account for central nervous system activities. Spatial dynamics may be a practical solution. The general hypothesis that measurements of changes in fundamental brain variables, action potentials, transmitter releases, post-synaptic transmembrane currents, etc., propagating in central nervous systems reveal how they work, carries no additional assumptions. Combinations of current techniques could reveal many aspects of spatial dynamics of spiking, post-synaptic processing, and plasticity in insects and rodents to start with. But problems defining baseline and reference conditions hinder interpretations of the results. Furthermore, the facts that pooling and averaging of data destroy their underlying dynamics imply that single-trial designs and statistics are necessary.

Updates to the guinea pig animal model for in-vivo auditory neuroscience in the low-frequency hearing range

For gaining insight into general principles of auditory processing, it is critical to choose model organisms whose set of natural behaviors encompasses the processes being investigated. This reasoning has led to the development of a variety of animal models for auditory neuroscience research, such as guinea pigs, gerbils, chinchillas, rabbits, and ferrets; but in recent years, the availability of cutting-edge molecular tools and other methodologies in the mouse model have led to waning interest in these unique model species. As laboratories increasingly look to include in-vivo components in their research programs, a comprehensive description of procedures and techniques for applying some of these modern neuroscience tools to a non-mouse small animal model would enable researchers to leverage unique model species that may be best suited for testing their specific hypotheses. In this manuscript, we describe in detail the methods we have developed to apply these tools to the guinea pig animal model to answer questions regarding the neural processing of complex sounds, such as vocalizations. We describe techniques for vocalization acquisition, behavioral testing, recording of auditory brainstem responses and frequency-following responses, intracranial neural signals including local field potential and single unit activity, and the expression of transgenes allowing for optogenetic manipulation of neural activity, all in awake and head-fixed guinea pigs. We demonstrate the rich datasets at the behavioral and electrophysiological levels that can be obtained using these techniques, underscoring the guinea pig as a versatile animal model for studying complex auditory processing. More generally, the methods described here are applicable to a broad range of small mammals, enabling investigators to address specific auditory processing questions in model organisms that are best suited for answering them.

Cystatin C promotes cognitive dysfunction in rats with cerebral microbleeds by inhibiting the ERK/synapsin Ia/Ib pathway

Although higher serum level of cystatin C (CysC) was observed in patients with cerebral microbleeds, its associated role in the disease has not been elucidated. In this work, a rat model of cerebral microbleeds was created with the aim of investigating effects of CysC on cognitive function in rats with cerebral microbleeds and the underlying mechanism. Serum samples of patients with cerebral microbleeds and healthy people of the same age were collected. Levels of cystatin C expression in these samples were measured using CysC kits. Moreover, 48 spontaneously hypertensive rats (SHRs) bred under specific pathogen-free (SPF) conditions were randomly divided into 4 groups: sham surgery control group (sham), model group (CMB), model + empty vector control group (CMB + vehicle), and model + cystatin C overexpression group (CMB + CysC). Expression levels of CysC in hippocampus of rats in each group were measured by western blot analysis. The Y-maze was used to evaluate cognitive function of rats. Hippocampal long-term potentiation (LTP) in rats was assessed by the electrophysiological assay. Alterations in levels of p-ERK1/2 and p-synapsin Ia/b proteins associated with cognitive function were identified by western blot analysis. The serum levels of CysC in patients with cerebral microbleeds were significantly upregulated (P<0.001). After injection of CysC, its expression levels in rat hippocampus were significantly increased (P<0.001), which enhanced the decline in learning and memory function, as well as the decrease of LTP in the rat model of cerebral microbleeds (P<0.001). Western blot results showed that injection of CysC further reduced the levels of p-ERK1/2 and p-synapsin Ia/b in the rat model of microbleeds (P<0.001). CysC was up regulated in serum of patients with cerebral microbleeds. It promoted cognitive dysfunction in rats with microbleeds by inhibiting ERK/synapsin Ia/Ib pathway.