The goal of this project is to adapt diffusive optical imaging (DOI) to study the brains of songbirds. We study songbirds because they have a special ability to learn songs and to use them to communicate. We choose to use DOI because it has a unique potential for harmlessly measuring the brain activity of birds as they experience and process songs. The measurements of brain activity can be taken during any stage of learning – from the time birds first hear a song to, in principle, the time they first produce a song they have learned. Moreover, DOI may allow us to do this over the course of experience, development, and time, all in the same bird, and without any pharmacologic intervention such as sedation or anesthesia. It is the goal of this dissertation to adapt DOI to the study of songbirds and to find directions for further development.Songbirds communicate by learned vocalizations with concomitant changes in neurophysiological and genomic activities in discrete parts of the brain. The research presented here tests a novel implementation of DOI for monitoring brain physiology associated with vocal signal perception. DOI noninvasively measures brain activity using red and near-infrared light delivered through optic fibers (optodes) resting on the scalp. DOI does not harm the subject, so it raises the possibility of repeatedly measuring brain activity while leaving tissue intact for further study. We developed a custom-made apparatus for interfacing optodes to the zebra finch (Taeniopygia guttata) head using 3D modeling software and rapid prototyping technology and applied it to record responses to presentations of birdsong in isoflurane-anesthetized zebra finches. We discovered a subtle but significant difference between the hemoglobin spectra of zebra finches and mammals which has a major impact in how hemodynamic responses are interpreted in the zebra finch. Our measured responses to birdsong playback were robust, highly repeatable, and readily observed in single trials. Responses were complex in shape and closely paralleled responses described in mammals. They were also localized to the caudal medial portion of the forebrain, as expected from prior gene expression, electrophysiological, and functional magnetic resonance imaging studies. We then expanded upon design methods described in our earlier study to create a helmet-interface to couple optic fibers to the scalp and applied it to record responses to presentations of various auditory stimuli in awake unanesthetized birds. We measured and compared responses to birdsong and a series of tones of frequencies found in birdsong. Our findings revealed that awake birds have different features and latencies in the hemodynamic response compared to lightly isoflurane-anesthetized birds. The optically-measured hemodynamic response also demonstrates striking stimulus-specificity to conspecific birdsong versus to a series of tones. These data demonstrate the feasibility of recording meaningful optical responses from awake songbirds using a helmet interface. The importance of this approach is underscored by the discrepancy between awake and anesthetized responses. Finally, we demonstrate the capability of our implementation of DOI to detect a basic form of learning in awake zebra finches: rapid habituation to playback of birdsong. Each bird was exposed to a different sequence of novel songs, where each song was played multiple times before switching to the next novel song in the sequence. When a given novel song was initially played, we recorded several large-amplitude responses to each repetition. As more repetitions were played, we observed the hemodynamic response amplitude rapidly decrease with continued repeated presentations of the same song (habituation). During switches to new songs in the sequence, a relatively large amplitude response would initially result. These, in turn, were also followed by habituation with repeated presentations shortly afterwards. When a switch was made to a song the bird had already habituated to earlier in the sequence, the response amplitude remained at its already-habituated level. A last novel song was then presented, and the large amplitude response was seen again. This shows that the low amplitude response to the familiarized stimulus was not due to stimulus fatigue and that the bird was indeed capable of producing a large response. These findings are consistent with habituation. The findings of this study are also consistent with those from earlier electrophysiology studies done in songbirds. These findings establish the feasibility of using DOI to detect evidence of learning. Together, the results of the research presented here define an approach for collecting neurophysiological data from songbirds that is both noninvasive, and applicable with and without pharmacological intervention. We have demonstrated that the method is capable of discerning the complexity of auditory stimuli presented to songbirds (song versus tone), and is able to detect evidence of learning (song habituation). It is rapid, inexpensive, and it reliably records responses in single trials. It may be used to conduct studies to interpret the effect of anesthesia through comparison to with awake-animal responses. Used in conjunction with molecular, genomic, or any other terminal or invasive procedure, this implementation of DOI may greatly enhance the amount of information which may be gained from each subject since this method leaves them unharmed. Finally, the approach used to apply DOI and to generate the equipment and interfaces for songbirds should be applicable to scarce and diverse species as well.
【 预 览 】
附件列表
Files
Size
Format
View
Development of diffusive optical imaging as a tool for studying the neurobiology of birdsong
PDF
download
878987797
028-85220240
