Conspecific song preference is the ability songbirds require to distinguish conspecific song from heterospecific song in order for females to choose an appropriate mate, and for juvenile males to choose an appropriate song tutor during vocal learning. Researchers studying the swamp sparrow (Melospiza georgiana) have demonstrated that young birds are born with this ability, because juvenile males raised in acoustic isolation and tutored with artificial recordings choose to learn only songs that contain their own species' syllables. [1] Studies conducted at later life stages indicate that conspecific song preference is further refined and strengthened throughout development as a function of social experience. [2] The selective response properties of neurons in the songbird auditory pathway has been proposed as the mechanism responsible for both the innate and acquired components of this preference.
The mechanism responsible for the ability to distinguish song types has not yet been fully characterized by researchers in the field of neuroethology, but it has been demonstrated that at least five different structures within the auditory pathway contain neurons that preferentially respond to conspecific song. The structure of neural networks, the morphology of neurons, and the receptor and ion channel complement of pre-synaptic connections cause some neurons to respond maximally to a particular stimulus frequency, phase, amplitude or temporal pattern, and this is known as spectral-temporal tuning. [3] Tight spectral-temporal tuning in the auditory pathway provides the central nervous system of songbirds with the ability to discriminate between conspecific and heterospecific songs. Tuning characteristics of auditory neurons have been best characterized in zebra finch (Taeniopygia guttata), canary (Serinus canaria), European starling (Sturnus vulgaris) and Western barn owl (Tyto alba).
The conventional song system of songbirds has two parts: the anterior forebrain pathway (AFP) involved in song learning, and the posterior forebrain pathway or "song motor pathway" (PFP/SMP) involved in song production. Both of these descending pathways contain neurons that are responsive to conspecific song. [4] Female Canaries lost the ability to discriminate between conspecific and heterospecific song after bilateral lesions to the high vocal center HVC, a nucleus that sits at the apex of both pathways. [5] In males, however, most song system neurons respond maximally to the sound of the bird's own song, even more than they do to the tutor's song or any other conspecific song. [6] [7] In HVC, neurons switch from responding best to tutor song (35–69 days post-hatch) to responding best to the bird's own song (>70 days post-hatch). [8] Song preferences of neurons in these pathways are important for sensorimotor learning, however several lines of evidence suggest that the specific ability to discriminate conspecific from heterospecific song does not reside in the AFP or the SMP. Most importantly, gene expression studies have demonstrated that, as a broad unit, neurons in the AFP and SMP show increased activation when a bird is singing, but not when it is simply listening to song. [9] With the exception of female Canaries, the neural substrate for conspecific song preference is thought to reside outside the conventional song system, in the auditory pathway. [10] [11]
Avian hair cells have been extensively studied in the cochlea of the barn owl, [12] and it is now known that both the morphological structure of hair cell papillae and the ion channels that characterize hair cell membranes confer spectral tuning properties. Ca2+ dependent K+ channels are produced as splice variants of the cSlo gene, [13] and different isoforms cause the hair cell to preferentially respond to different resonant frequencies. [14] [15] Species-specific differences in cSlo isoforms of hair cell membranes may therefore play a role in the discrimination of conspecific and heterospecific notes in songbirds.
Studies on zebra finch have shown that nuclei in the auditory thalamus, two steps up from the cochlea, do not passively relay input from peripheral sensory structures into higher forebrain structures. Thalamic nuclei show different patterns of gene expression in response to different stimuli, implicating them in the process of acoustic discrimination. [16] Neurons in the nucleus ovoidalis (Ov) have receptive fields that are tuned to respond to the specific combination of spectral and temporal features present in syllables of conspecific song. Stimulus-selective tuning is determined by the receptor proteins and ion channels characterizing synapses of these neurons. Neurons can selectively respond to time-based differences between songs (e.g. syllable length or syllable-interval length) if they are post-synaptic to either fast-release (ionotropic) or slow-release (metabotropic) glutamate receptors. [17] [18]
Strong conspecific-selective responses have been most consistently demonstrated in neurons of the higher-level structures of the auditory system: The caudomedial neostriatum (NCM), [19] [20] the auditory thalamo-recipient subfield (Field L: L1, L2a, L2b, L3), [2] [21] and the caudal mesopallium (CM: CMM and CLM). [22] [23] [24] [25] NCM and CM have been known to be discussed in conjunction with one another being as they are functionally similar. Recent studies have begun to show that while that is true, CM seems to respond in a manner relative to whether or not the stimulus is personally significant to the bird.
In European starlings, neurons in NCM habituate to a particular stimulus, and “remember” individual characteristics of songs to which a bird was exposed. This indicates that NCM functions in individual recognition, through the strategic recruitment of N-Methyl-D-aspartate receptors (NMDAR) to synapses that receive repeated patterns of excitation. [23] [26] In fact, NMDARs are thought to be the unit broadly responsible for synaptic memory in the central nervous system. NMDARs in NCM neurons, therefore, might be a compelling target for selection when song functions in discrimination among conspecific songs, for neighbor recognition and territorial defense, but NCM is unlikely to play a role in the discrimination of conspecific from heterospecific songs.
In male zebra finches, neurons in Field L and CM do not exhibit a preference for different types of conspecific songs (in contrast to neurons in NCM, and those that participate in the AFP and SMP). Field L and CM neurons do not discriminate between the tutor song, the bird's own song, or individual conspecifics. [27] Instead, they demonstrate a higher-order preference for conspecific song over heterospecific song or other types of sound. [2] [22] When male and female European starlings are trained to recognize conspecific song, there is an associated change in the response of CMM neurons, [28] and female zebra finches experience a reduced ability to discriminate between conspecific and heterospecific song following lesions to the region. [29] However, CMM neurons in females also show increased activation in response to their father's song over a novel conspecific song, demonstrating that this nucleus also participates in some selectivity among conspecific songs in females. [30] [31] [32]
Neurons in both Field L and CM have sophisticated filter properties, selective for both the spectral-temporal modulations and phase relationships of conspecific songs. [24] Furthermore, different neurons are selective for different features of syllables and songs. In Field L, neurons have one of four different tuning strategies—they are either tightly tuned a particular frequency, or they are sensitive to frequency edges, frequency sweeps or combined frequencies. [33] [34] When exposed to natural song as a stimulus, different ensembles of these of neurons respond to different components of sound, and together they demonstrate the ability to perform sensitive discrimination between conspecific and heterospecific syllable types. As in nucleus ovoidalis, the spectral-temporal filter properties of Field L and CM neurons are a function of the particular ion channels and receptor proteins driving their synaptic dynamics. The complex and sophisticated tuning of these higher order processing centers for conspecific sounds may rely on the integrated inputs from the entire ascending auditory pathway, from the hair cells through the thalamus and forebrain, but this challenging synthetic question remains to be investigated.
In an evolutionary context, neural mechanisms of conspecific song preference in the auditory pathway are important for species recognition. Species recognition traits play a central role in both the origin and maintenance of reproductive isolation. Furthermore, a shared neural mechanism for conspecific song preference has implications for the coevolution of male song and female preference, which may help explain the dramatic diversity of song phenotypes in extant songbirds<.
Bird vocalization includes both bird calls and bird songs. In non-technical use, bird songs are the bird sounds that are melodious to the human ear. In ornithology and birding, songs are distinguished by function from calls.
The receptive field, or sensory space, is a delimited medium where some physiological stimuli can evoke a sensory neuronal response in specific organisms.
The auditory cortex is the part of the temporal lobe that processes auditory information in humans and many other vertebrates. It is a part of the auditory system, performing basic and higher functions in hearing, such as possible relations to language switching. It is located bilaterally, roughly at the upper sides of the temporal lobes – in humans, curving down and onto the medial surface, on the superior temporal plane, within the lateral sulcus and comprising parts of the transverse temporal gyri, and the superior temporal gyrus, including the planum polare and planum temporale.
The Society finch, also known as the Bengali finch or Bengalese finch, is a domesticated subspecies of finch. It became a popular cage and trade bird after appearing in European zoos in the 1860s through being imported from Japan, though it was domesticated in China. Coloration and behavior were modified through centuries of selection in Asia, then later in Europe and North America.
In neuroscience, neuronal tuning refers to the hypothesized property of brain cells by which they selectively represent a particular type of sensory, association, motor, or cognitive information. Some neuronal responses have been hypothesized to be optimally tuned to specific patterns through experience. Neuronal tuning can be strong and sharp, as observed in primary visual cortex, or weak and broad, as observed in neural ensembles. Single neurons are hypothesized to be simultaneously tuned to several modalities, such as visual, auditory, and olfactory. Neurons hypothesized to be tuned to different signals are often hypothesized to integrate information from the different sources. In computational models called neural networks, such integration is the major principle of operation. The best examples of neuronal tuning can be seen in the visual, auditory, olfactory, somatosensory, and memory systems, although due to the small number of stimuli tested the generality of neuronal tuning claims is still an open question.
The spectro-temporal receptive field or spatio-temporal receptive field (STRF) of a neuron represents which types of stimuli excite or inhibit that neuron. "Spectro-temporal" refers most commonly to audition, where the neuron's response depends on frequency versus time, while "spatio-temporal" refers to vision, where the neuron's response depends on spatial location versus time. Thus they are not exactly the same concept, but both are referred to as STRF and serve a similar role in the analysis of neural responses.
The cochlear nucleus (CN) or cochlear nuclear complex comprises two cranial nerve nuclei in the human brainstem, the ventral cochlear nucleus (VCN) and the dorsal cochlear nucleus (DCN). The ventral cochlear nucleus is unlayered whereas the dorsal cochlear nucleus is layered. Auditory nerve fibers, fibers that travel through the auditory nerve carry information from the inner ear, the cochlea, on the same side of the head, to the nerve root in the ventral cochlear nucleus. At the nerve root the fibers branch to innervate the ventral cochlear nucleus and the deep layer of the dorsal cochlear nucleus. All acoustic information thus enters the brain through the cochlear nuclei, where the processing of acoustic information begins. The outputs from the cochlear nuclei are received in higher regions of the auditory brainstem.
The dorsal cochlear nucleus is a cortex-like structure on the dorso-lateral surface of the brainstem. Along with the ventral cochlear nucleus (VCN), it forms the cochlear nucleus (CN), where all auditory nerve fibers from the cochlea form their first synapses.
The interaural time difference when concerning humans or animals, is the difference in arrival time of a sound between two ears. It is important in the localization of sounds, as it provides a cue to the direction or angle of the sound source from the head. If a signal arrives at the head from one side, the signal has further to travel to reach the far ear than the near ear. This pathlength difference results in a time difference between the sound's arrivals at the ears, which is detected and aids the process of identifying the direction of sound source.
A song system, also known as a song control system (SCS), is a series of discrete brain nuclei involved in the production and learning of song in songbirds. It was first observed by Fernando Nottebohm in 1976 in a paper titled "Central control of song in the canary, Serinus canarius", published in the Journal of Comparative Neurology.
HVC is a nucleus in the brain of the songbirds necessary for both the learning and the production of bird song. It is located in the lateral caudal nidopallium and has projections to both the direct and the anterior forebrain pathways.
Vocal learning is the ability to modify acoustic and syntactic sounds, acquire new sounds via imitation, and produce vocalizations. "Vocalizations" in this case refers only to sounds generated by the vocal organ as opposed to by the lips, teeth, and tongue, which require substantially less motor control. A rare trait, vocal learning is a critical substrate for spoken language and has only been detected in eight animal groups despite the wide array of vocalizing species; these include humans, bats, cetaceans, pinnipeds, elephants, and three distantly related bird groups including songbirds, parrots, and hummingbirds. Vocal learning is distinct from auditory learning, or the ability to form memories of sounds heard, a relatively common trait which is present in all vertebrates tested. For example, dogs can be trained to understand the word "sit" even though the human word is not in its innate auditory repertoire. However, the dog cannot imitate and produce the word "sit" itself as vocal learners can.
An organism is said to be sexually dimorphic when male and female conspecifics have anatomical differences in features such as body size, coloration, or ornamentation, but disregarding differences of reproductive organs. Sexual dimorphism is usually a product of sexual selection, with female choice leading to elaborate male ornamentation and male-male competition leading to the development of competitive weaponry. However, evolutionary selection also acts on the sensory systems that receivers use to perceive external stimuli. If the benefits of perception to one sex or the other are different, sex differences in sensory systems can arise. For example, female production of signals used to attract mates can put selective pressure on males to improve their ability to detect those signals. As a result, only males of this species will evolve specialized mechanisms to aid in detection of the female signal. This article uses examples of sex differences in the olfactory, visual, and auditory systems of various organisms to show how sex differences in sensory systems arise when it benefits one sex and not the other to have enhanced perception of certain external stimuli. In each case, the form of the sex difference reflects the function it serves in terms of enhanced reproductive success.
Feature detection is a process by which the nervous system sorts or filters complex natural stimuli in order to extract behaviorally relevant cues that have a high probability of being associated with important objects or organisms in their environment, as opposed to irrelevant background or noise.
Binocular neurons are neurons in the visual system that assist in the creation of stereopsis from binocular disparity. They have been found in the primary visual cortex where the initial stage of binocular convergence begins. Binocular neurons receive inputs from both the right and left eyes and integrate the signals together to create a perception of depth.
The torus semicircularis is a region of the vertebrate midbrain that contributes to auditory perception, studied most often in fish and amphibians. It corresponds to the inferior colliculus.
Sarah M. N. Woolley is a neuroscientist and Professor of Psychology at Columbia University's Zuckerman Institute. Her work centers on the neuroscience of communication, using songbirds to understand how the brain learns and understands vocal communication.
Jessica Cardin is an American neuroscientist who is an associate professor of neuroscience at Yale University School of Medicine. Cardin's lab studies local circuits within the primary visual cortex to understand how cellular and synaptic interactions flexibly adapt to different behavioral states and contexts to give rise to visual perceptions and drive motivated behaviors. Cardin's lab applies their knowledge of adaptive cortical circuit regulation to probe how circuit dysfunction manifests in disease models.
Adult neurogenesis is the process in which new neurons are born and subsequently integrate into functional brain circuits after birth and into adulthood. Avian species including songbirds are among vertebrate species that demonstrate particularly robust adult neurogenesis throughout their telencephalon, in contrast with the more limited neurogenic potential that are observed in adult mammals after birth. Adult neurogenesis in songbirds is observed in brain circuits that underlie complex specialized behavior, including the song control system and the hippocampus. The degree of postnatal and adult neurogenesis in songbirds varies between species, shows sexual dimorphism, fluctuates seasonally, and depends on hormone levels, cell death rates, and social environment. The increased extent of adult neurogenesis in birds compared to other vertebrates, especially in circuits that underlie complex specialized behavior, makes birds an excellent animal model to study this process and its functionality. Methods used in research to track adult neurogenesis in birds include the use of thymidine analogues and identifying endogenous markers of neurogenesis. Historically, the discovery of adult neurogenesis in songbirds substantially contributed to establishing the presence of adult neurogenesis and to progressing a line of research tightly associated with many potential clinical applications.
David Forrest Clayton is an American neuroscientist, biochemist, and academic. He is professor and the chair of the Department of Genetics & Biochemistry at Clemson University.