Michale S. Fee - US grants

A central issue in brain function is how patterns of sequential neural activity are created to produce sophisticated motor patterns in activities such as communication behavior, ranging from mating calls to language. In well-studied songbirds, singing-related activity occurs in a region known as RA (robust nucleus of the archistriatum), where individual neurons generate highly reproducible patterns of high-frequency bursts. Onsets and endings of these bursts show temporal correlations across large populations of neurons in this region, suggesting that RA undergoes synchronized transitions from one state of active neurons to another. The goal of this project is to develop models of how such sequence generation can occur, and test these models experimentally. A unique approach is used with a novel technology for stable cellular recordings from a sleeping bird, in which such structured bursts occur with patterns apparently 'replaying' the patterns produced during actual singing.
Results will be important for understanding mechanisms of sequence generation and of motor learning in the vertebrate brain, and could have an impact extending to mechanisms of human speech production. This combined computational and experimental work also provides a young PI with a cross-disciplinary experience that includes university-industry collaboration.

DESCRIPTION (provided by applicant): The proposed research aims at a mechanistic description of how complex motor sequences are generated and learned by brain circuits. Over the last decade, the songbird has emerged as an intriguing and approachable model system in which to pursue this problem. Songbirds learn their songs by trial-and-error experimentation, producing highly variable vocalizations as juveniles. By comparing their utterances to a memory of their tutor's song, their vocalizations gradually converge onto those of the tutor. The finished product is a stereotyped sequence of syllables that is driven by two forebrain motor nuclei, HVC, and RA (a motor cortex analogue). We believe that a key feature of the learning algorithm is the motor exploration that allows the bird to search for the right sound patterns. But what is the origin of this vocal exploration and how does it arise in the motor system? Aside from HVC, nucleus RA also receives excitatory projections from the lateral magnocellular nucleus of the nidopallium (LMAN), the output of a cortical-basal ganglia circuit. This circuit is not necessary for singing in adult birds, but is crucial for song learning. We recently found that inactivating LMAN largely abolishes the variability of juvenile song. Furthermore, we found that during singing, LMAN neurons that project to RA generate highly variable patterns of spikes and bursts. These observations led us to suggest that the LMAN input to RA directly drives vocal exploration in juvenile birds. We hope to build on these initial observations and address the following questions - How are the variable spike patterns in LMAN generated and how are they related to motor exploration? Since LMAN is the output of a well conserved basal ganglia circuit, understanding how this circuit contributes to variability in songbirds may shed light on motor learning in humans as well as speak to the role of the basal ganglia in motor function. Our goals are summarized in the following specific aims: Specific Aim 1: To determine the relative contribution of LMAN and HVC to the generation of juvenile song. Specific Aim 2: To characterize the correlation between LMAN firing and vocal output in the juvenile bird. Specific Aim 3: To determine where song variability is generated. Specific Aim 4: To measure the effect of LMAN input on the firing patterns of single RA neurons. PUBLIC HEALTH RELEVANCE Vocal exploration and learning in songbirds involve a basal ganglia-related (BG) circuit. The shared design of this avian circuit and mammalian BG circuitry implies that the neural mechanisms of song learning are likely to be directly relevant to mammalian BG and human disease. Disorders of BG circuitry lead to the impairments of serial processing and sequential behaviors observed in Parkinson's disease, schizophrenia, obsessive-compulsive disorder, Huntington's and the tardive syndromes.

This proposal attempts to create a flexible glucose fuel cell and associated ultra-low-power bioelectronics for self-powered brain implants of the future. The flexible glucose fuel cell enables a 20x increase in volumetric density with 320 uW of power available from a biocompatible 1cm (d) x 4 cm (l) device, which is implanted in the subarachnoid spaces of the brain and spinal cord. Thus, fully implantable brain implants for paralysis with novel state-of-the-art ultra-low-power electronics for neural recording, stimulation, decoding, and wireless communication, which consume 95 uW in total, can be powered with a safety factor of 3x that allows for fuel-cell output variation over time. This proposal attempts to test a fully functional brain-implant system in a smaller geometry 3 mm (d) x 3mm (l) device in a rat to ensure chronic (> 6 months) long-term biocompatibility and performance that meets our power budget. The use of the cerebrospinal fluid as a power source, which has a 200x lower protein count, and almost million-fold lower cell count, and only a 2x lower glucose content, provides a novel site for implantation significantly different from prior work in blood plasma or interstitial fluid. This novel intended site of implantation along with our use of materials and techniques that have been proven to increase biocompatibility, such as Nafion encapsulation, enhance longevity. The flexible glucose fuel cell will be fabricated using well-known semiconductor fabrication techniques on a silicon wafer enabling manufacturing scalability and ease of integration with electronics on the same wafer.

Intellectual Merit:
This work combines innovations and knowledge from several disciplines to potentially create a paradigm-changing capability in the field of medical implants: 1) Prior enzyme-based glucose fuel cells have been plagued by enzyme-degradation issues that have led them to be inefficient after a few short-term months. Abiotic fuel cells are more suited for long-term chronic operation but have relatively low power outputs. The creation of an abiotic flexible glucose fuel cell increases the volumetric density of available power by more than an order of magnitude while preserving the benefits of long-term abiotic operation. 2) The use of ultra-low-power bioelectronics that achieves state-of-the-art performance in all aspects of a brain-implant system enables miniature glucose fuel cells to meet the power budget needed for intended medical applications with even a safety factor of 3x and to fit within tightly constrained body spaces. 3) The use of standard semiconductor fabrication techniques enables entire flexible medical implants with their own power source and electronics to be cheaply fabricated in a rolled-up geometry without sacrificing performance as in systems made with flexible organic electronics. 4) The glucose-rich cerebrospinal fluid is highly abiotic (free of cells) and highly protein free making it an ideal source for providing fuel while not causing electrode bio-fouling. This work could enable glucose fuel cells to become practical after four decades of research.

Broader Impact:
Glucose fuel cells have use in the treatments of cardiac arrhythmia, diabetes, epilepsy, deep brain disorders, and cancer tumor monitoring. Rolled-up ?sugar powered batteries? may be used in non-invasive wireless medical monitoring or in wearable and flexible electronic systems. The flexible glucose fuel cell can help solve a national challenge for non-toxic (unlike batteries), renewable, carbon-neutral, energy sources that are practical. The PI plans to introduce an in-vitro glucose-fuel-cell powered ECG as a project in his course in bioelectronics at MIT that has been taught for over 10 years at MIT The Research Team further plans to develop a module that will use microfluidic setup to monitor output protein concentrations in cells at the fuel-cell output voltages and introduce the platform to the do-it-yourself community at MIT through programs such as Lifelong Kindergarten and ?Science Saturday? at Lincoln Lab. The PI plans to recruit under-represented students from his active participation in the admissions programs of the Computational and Systems Biology, Biophysics, Synthetic Biology, and Bioelectrical endeavors at MIT. The investigators will participate in SEED (Saturday Engineering Enrichment and Discovery) Academy, which enrolls students from Boston, Cambridge, and Lawrence Public Schools; they will also work closely with the Society of Women Engineers (SWE) to attract promising young women into biomedical and bioengineering research; and, they will work actively with the MIT Summer Research Program (MSRP), which has traditionally included underrepresented students into research programs. Thus the proposal will have broad technical impact, broad educational impact, and broaden societal participation.