F behavioral plasticity F CH8: development of learning in songbirds F behavioral analysis of birdsong F singing in the brain F summary PART 4: BEHAVIORAL PLASTICITY #17: DEVELOPMENT OF LEARNING IN SONGBIRDS II

PART 4: BEHAVIORAL PLASTICITY #17: DEVELOPMENT OF LEARNING IN SONGBIRDS II F behavioral plasticity F CH8: development of learning in songbirds F behavioral analysis of birdsong F singing in the brain F summary

F song structures... 2 pathways F song production pathway  F anterior forebrain pathway ... not directly related to song production F found only in birds that F learn to sing F use feedback ANATOMY

F song structures... 2 pathways F song production pathway   higher vocal center  robust nucleus of the archistriatum  tracheosyringeal portion of the hypoglossal nucleus  syringeal musculature F anterior forebrain pathway  ANATOMY

F song structures... 2 pathways F song production pathway  F anterior forebrain pathway   area X  medial portion of the dorsolat. thalamus  lateral portion of the magnocellular nucleus of the anterior neostriatum ANATOMY

F pathways interconnected at several points F oversimplified here (!)... most studied illustrated only F other bits and connections not discussed... eg ANATOMY

F some functions carried out primarily / exclusively by 1 side of the brain... laterality... many familiar eg s F syrinx innervated by L & R hypoglossal nerve XII LATERALITY

F transect R side F modest effect F transect L side F severe effect F hypoglossal dominance F some functions carried out primarily / exclusively by 1 side of the brain... laterality... many familiar eg s F syrinx innervated by L & R hypoglossal nerve XII LATERALITY

F interesting observations... some spp. of birds are hypoglossal dominant... F left (chaffinch, canaries) F right (zebra finches) F neither LATERALITY

F laterality in other systems higher in the brain... F lesions in brain...HVc in adult canaries... F R lesions mile F L lesions severe F hemispheric dominance LATERALITY

F permanent effect of HVc lesions in canaries ? F can gradually relearn song F lesions overcome by HVc in R hemisphere F subsequent lesion in R HVc F removes song permanently F cellular mechanisms not well understood known LATERALITY

F neural changes in identified structures / seasons ? F in adults... in spring ( vs fall) sizes of F HVc 99% increased F RA 76% increased F ~ increased song repertoire SEASONAL VARIATION & NEUROGENESIS

F HVc & RA F ~ increased song repertoire in  s &  s F in  s (non-singers) <  s F increase in  s + testosterone SEASONAL VARIATION & NEUROGENESIS

F how to increase brain size ? F new neurons... neurogenesis F new projections F new synapses... synaptogenesis F all of the above ? F important questions about “adult” nervous systems: F are new neurons born ? F do they connect properly ? F do they function properly ? SEASONAL VARIATION & NEUROGENESIS

F some birds show F seasonal variation in anatomy & song F no seasonal variation in anatomy but do have seasonal changes in song... F HVc size increase accompanied by neurogenesis F intriguing hypothesis: replacement of old neurons with new ones as birds replace old songs with new ? SEASONAL VARIATION & NEUROGENESIS

F neurogenesis in songbirds F 20 – 65 days post-hatching F new neurons added to HVc & area X F occurs in  s >  s (non-singers) F 50% project from HVc  RA F ~ song learning sensitive phase F sexual dimorphism SEASONAL VARIATION & NEUROGENESIS

F new neurons during sensory or sensorimotor phase ? F can’t address in zebra finch, phases overlap F in white-crowned sparrow... F change during peak of sensory acquisition phase F little change in sensory motor phase F  in swamp sparrow, neurogenesis  song learning SEASONAL VARIATION & NEUROGENESIS

F not important for normal song production... but F important for sensory learning & auditory matching F juvenile zebra finches... lesions in LMAN disrupts F  subsequent learning of song F not needed for song maintenance F similar results found for area X & DLM ANTERIOR FOREBRAIN PATHWAY

F what kinds of information processed by pathway ? F lesions in zebra finches F LMAN  monotonous repetition, 1-note clusters, arrests further song plasticity (premature stabilization) F area X  rambling & long F authors suggest LMAN  F sends feedback  area X F maintain plasticity in RA F site of steroid hormone activity ANTERIOR FOREBRAIN PATHWAY

F song production F in HVc & RA... premotor areas F neuron activation before, during, after song F activity in HVc precedes RA F HVc for whole song F RA for syllables CELLULAR ANALYSIS

F song production F in HVc & RA... premotor areas F stimulate HVc during singing, F phase advance of song F ~ reset of pattern F not ~ feedback F HVc neurons ~ song pattern generator F RA neurons receive signal, do not generate pattern CELLULAR ANALYSIS

F auditory selectivity F song feedback critical F response sites ? F anterior forebrain pathway CELLULAR ANALYSIS

F auditory selectivity F song feedback critical F response sites ? F anterior forebrain pathway F own song F reversed  F conspecific  CELLULAR ANALYSIS

F auditory selectivity F song feedback critical F response sites ? F anterior forebrain pathway F own song F reversed  F conspecific  F LMAN > area X... hierarchy F successive sites  greater selectivity CELLULAR ANALYSIS

F auditory selectivity F HVc RA (song production pathway) area X (anterior forebrain pathway) F projections from 2 distinct HVc cell populations F all 3 structures “selective” CELLULAR ANALYSIS

F auditory selectivity F caudal medial neostriatum (NCM) F gene transcription  regulated by conspecific song F immediate-early gene activation... zenk F rapid activation F response to signals F only on first exposure... involved in learning CELLULAR ANALYSIS

F compared F differential developmental timetables in song system F 2 pathways from HVc develop at different times 1. indirect HVc ...  2 weeks posthatch F ~ learning F template 1 st 2. direct HVc  3-4 weeks posthatch F ~ singing F own song 2 nd CELLULAR ANALYSIS

F differential developmental timetables in song system F 2 pathways from HVc develop at different times 1. indirect HVc ...  2 weeks posthatch 2. direct HVc  3-4 weeks posthatch F correlated innervation F different transmitters & receptors F different types of synapses  RA F convergence at RA ? CELLULAR ANALYSIS

F differential developmental timetables in song system F when are HVc neurons song-selective ? F white crown sparrows F not until after gap... during sensorimotor phase F not for tutoring (sensory) but for listening to self CELLULAR ANALYSIS

F sexual dimorphism in the bird brain F all song nuclei  >  F HVc volume ~ song complexity F  :  ~ song CELLULAR ANALYSIS

F sexual dimorphism in the bird brain F why do non-singing  s have song nuclei ? F some do sing in response to  song F lesion in HVc removes discriminative ability F important for song perception in  s F same circuitry used differently by  s &  s CELLULAR ANALYSIS

F bird song simple  complex F acoustic architecture: notes, syllables, phrases F species typical song + dialects F phases of song development F sensory: learning by example from others F sensory motor: subsong, plastic song F crystallized song: stable song F some spp. have overlap, some have separation SUMMARY

F auditory feedback critical for sensorimotor acquisition F song template = innate + learned components F song usually sexually dimorphic F steroid hormones  development, seasonal expression of song, song learning F 2 interacting & converging brain circuits (at RA): F song production pathway F anterior forebrain pathway SUMMARY

F auditory neurons selective for own song F sites for processing auditory feedback F sequential activation of HVc  RA premotor neurons F part of song pattern generator in HVc F anatomical sexual dimorphism ~ song generation F song nuclei important for song perception in  s SUMMARY