Hiroko Eda-Fujiwara

Neuronal activation in female budgerigars is localized and related to male song complexity

Females of several songbird species have been shown to respond preferentially to a more complex song. The male budgerigar (Melopsittacus undulatus) sings complex songs consisting of discrete components, known as syllables. We exposed female budgerigars to either standard male song, complex song, or simple song, the iteration of only one syllable (either frequency‐modulated or unmodulated). Using immunocytochemistry, we analysed the expression of the protein product of the immediate early gene ZENK in a number of forebrain regions. The level of Zenk protein expression caused by song stimuli varied among each of the brain regions. Expression was highest in the caudomedial neostriatum (NCM), lower in the caudomedial hyperstriatum ventrale (CMHV), and lowest in the hippocampus. There was a significant effect of song complexity on the number of Zenk‐immunoreactive cells in the NCM, but not in the hippocampus. Zenk protein expression correlated significantly and positively with the number of different syllables to which the females were exposed in the NCM and to a lesser extent in the CMHV, but not in the hippocampus. For the NCM this correlation was also significant within the group exposed to natural song. These results suggest that the NCM is involved in the perception of song complexity in female budgerigars.

What causes the aphid 28S rRNA to lack the hidden break

SummaryIn order to determine why the aphid 28S rRNA lacks the hidden break otherwise found in insects, the structure of the region of the aphid ribosomal DNA (rDNA) corresponding to the gap region, which in other insect rDNA transcripts is excised posttranscriptionally, was studied. Sequence comparison suggested that, in contradistinction to what is found in rDNA transcripts of other insects, a stem-loop structure formed in this region of the aphid rDNA transcript is not AU-rich. Nor did the loop of the aphid molecule contain the UAAU tract that can be a signal for the introduction of the hidden break, suggesting that in this particular region the aphid 28S rRNA resembles 28S rRNAs of deuterostomes, which do not contain the hidden break.

Sexual dimorphism of acoustic signals in the oriental white stork: non-invasive identification of sex in birds.

Abstract Identification of the sex of birds is important for captive breeding of endangered species. In the oriental white stork (Ciconia boyciana), an endangered species, both sexes produce an acoustic signal called “clatter” by rattling their mandibles together to generate sounds. We examined the structure of male and female clatter to determine whether clatter is sexually dimorphic. The acoustic structure of the clatter of the two sexes proved to be dimorphic with respect to the fundamental frequency; female clatter had higher fundamental frequencies. The fundamental frequency correlated significantly and positively with bill length, suggesting that bill morphology contributes to the sexual dimorphism of clatter. Sexing can be done by acoustic signals without capturing birds, and thus is useful as a non-invasive sexing method for ecological and conservation studies of birds.

Birdsong and the brain: the syntax of memory.

In this issue, Kato et al. use expression of immediate early genes to show that the caudomedial pallium of female Bengalese finches is particularly responsive to the phonology of male song and not to the sequence of its elements. We discuss the significance of these findings in the wider framework of birdsong in songbirds and parrots, which has become a prominent model system for the neurobiology of learning, memory and perception. Male song is an important signal in songbird sexual selection, and females show behavioural and neural preferences for particular songs or song elements. In addition, birdsong learning is increasingly seen as the closest animal equivalent to the acquisition of speech and language in humans.

Localized Brain Activation Related to the Strength of Auditory Learning in a Parrot

Parrots and songbirds learn their vocalizations from a conspecific tutor, much like human infants acquire spoken language. Parrots can learn human words and it has been suggested that they can use them to communicate with humans. The caudomedial pallium in the parrot brain is homologous with that of songbirds, and analogous to the human auditory association cortex, involved in speech processing. Here we investigated neuronal activation, measured as expression of the protein product of the immediate early gene ZENK, in relation to auditory learning in the budgerigar (Melopsittacus undulatus), a parrot. Budgerigar males successfully learned to discriminate two Japanese words spoken by another male conspecific. Re-exposure to the two discriminanda led to increased neuronal activation in the caudomedial pallium, but not in the hippocampus, compared to untrained birds that were exposed to the same words, or were not exposed to words. Neuronal activation in the caudomedial pallium of the experimental birds was correlated significantly and positively with the percentage of correct responses in the discrimination task. These results suggest that in a parrot, the caudomedial pallium is involved in auditory learning. Thus, in parrots, songbirds and humans, analogous brain regions may contain the neural substrate for auditory learning and memory.

Effects of deafening on the temporal pattern of vocalizations in the budgerigarMelopsittacus undulatus

The physical characteristics of vocalization were examined in budgerigars (Melopsittacus undulatus) deafened at the age of about 28 days. Autocorrelation was used in the analysis, with 2 parameters: 1) inter-element intervals and 2) amplitudes of all sound elements of the vocalization. The deafened birds developed the temporal pattern specific to normal warble song in autocorrelograms. However, abnormalities were found in the frequency spectrum of elements. The temporal pattern of warble song might be an innate character, because auditory feedback is unnecessary for its development.

Sex differences in behavioural and neural responsiveness to mate calls in a parrot

Vocalisation in songbirds and parrots has become a prominent model system for speech and language in humans. We investigated possible sex differences in behavioural and neural responsiveness to mate calls in the budgerigar, a vocally-learning parrot. Males and females were paired for 5 weeks and then separated, after which we measured vocal responsiveness to playback calls (a call of their mate versus a call of an unfamiliar conspecific). Both sexes learned to recognise mate calls during the pairing period. In males, but not females, mate calls evoked significantly fewer vocal responses than unfamiliar calls at one month after separation. Furthermore, in females, there was significantly greater molecular neuronal activation in response to mate calls compared to silence in the caudomedial mesopallium (CMM), a higher-order auditory region, in both brain hemispheres. In males, we found right-sided dominance of molecular neuronal activation in response to mate calls in the CMM. This is the first evidence suggesting sex differences in functional asymmetry of brain regions related to recognition of learned vocalisation in birds. Thus, sex differences related to recognition of learned vocalisations may be found at the behavioural and neural levels in avian vocal learners as it is in humans.

Song preferences by females: male song complexity and gene expression in the female brain

ABSTRACT The males of songbirds, parrots and hummingbirds develop complex song through learning. Males of some species mimic the vocalizations of other species and make their song more complex through vocal mimicry. Females of several songbird species respond preferentially to more complex song. The sensory exploitation hypothesis is an explanation how female preferences for complex song historically came to exist in birds. Female response to song readily habituates to repeated presentation of simple (that is, monotonous) song, while complex song can reduce habituation in female response to song. Males singing complex song might have exploited such pre-existing property (or bias) in the females response to song. This explanation is supported by experiments involving measurement of the expression of immediate early genes (IEGs). Analysis of IEG expression has been useful to reveal brain activation patterns associated with specific sensory stimuli. When exposed to male song, female songbirds and parrots show increased IEG expression in the auditory system in the caudal telencephalon, notably the caudomedial nidopallium (NCM) and the caudomedial mesopallium (CMM). Current data from female brains suggest that the NCM is related to song complexity. In addition, both of the NCM and the CMM may be involved in discriminating conspecific from heterospecific vocalizations.

Androgen-induced sex differentiation in maturation process of extinction memory retention after conditioned taste aversion learning in mice

A pair-association (PA) task is widely used to examine the neural correlates concerning visual long-term memory. Animal studies suggest that the prefrontal cortex (PFC) provides top-down signals to the temporal cortex to retrieve appropriate information from long-term memory (LTM) while animals performed the PA task. Although previous studies show that the PFC is activated during encoding and retrieving processes of LTM and that mutual functional interactions are present between prefrontal and temporal cortices, the nature of the top-down signal was less explored. In the present experiment, we examined which area in the PFC is activated while human subjects perform a pair-association task and compared temporal patterns of activation between the PFC and other cortical areas to understand the nature of the top-down signal generated in the PFC. We tested five subjects: each took 6 training sessions to remember 6 pairs of Mandelbrot figures during 6 days. We then examined brain activity during PA performances and compared this activity with activity during delayed matching-to-sample (DMS) performances using an event-related fMRI. We found that the left middle frontal gyrus activation was higher in PA than DMS. These results indicate that the left middle frontal gyrus is an important area for generating top-down signals to retrieve appropriate information in the PA task. Research fund: KAKENHI (21240024).

The role of amygdala as a neural substrate for conditioned taste preference learning in mice

To clarify the molecular basis of motor learning, we investigated classical eyeblink conditioning by the combination of KO mice and pharmacological studies. We elucidated that the delay conditioning paradigm, in which the CS overlapped the US in time, is critically dependent on mGluR1 to PLC 4 signaling cascade in cerebellar PCs. Furthermore, we found that delay conditioning is severely impaired in KO mice deficient in cannabinoid CB1 receptor (CB1R). Intraperitoneal injection of the CB1 antagonist SR141716A (rimonabant) also caused severe impairment of delay conditioning to wild-type mice, indicating that endogenous cannabioid signaling through CB1 is essential for acquisition of delay conditioning. In this study, the relationship between the mGluR1 and cannabinoid signaling pathways in motor memory formation was also evaluated.