The photosensitive phase acts as a sensitive window for seasonal multisensory neuroplasticity in male and female starlings

Traditionally, research unraveling seasonal neuroplasticity in songbirds has focused on the male song control system and testosterone. We longitudinally monitored the song and neuroplasticity in male and female starlings during multiple photoperiods using Diffusion Tensor and Fixel-Based techniques. These exploratory data-driven whole-brain methods resulted in a population-based tractogram uncovering microstructural sexual dimorphisms in the song control system and beyond. Male brains showed microstructural hemispheric asymmetries, whereas females had higher interhemispheric connectivity, which could not be attributed to brain size differences. Only females with large brains sing but differ from males in their song behavior by showing involvement of the hippocampus. Both sexes experienced multisensory neuroplasticity in the song control, auditory and visual system, and the cerebellum, mainly during the photosensitive period. This period with low gonadal hormones might represent a ‘sensitive window’ during which different sensory and motor systems in telencephalon and cerebellum can be seasonally re-shaped in both sexes. ### Competing Interest Statement The authors have declared no competing interest. * A : Arcopallium AD : Axial diffusivity CA : Commisura anterior / anterior commissure CbL : Nucleus cerebellaris lateralis / lateral cerebellar nucleus CO : Chiasma opticum / optic chiasm CP : Commisura posterior / posterior commissure CSt : Caudal part of the lateral striatum DLM : Nucleus dorsolateralis anterior thalami pars medialis / medial part of the dorsolateral nucleus of the anterior thalamus DMA : Dorsomedial nucleus of the anterior thalamus DMP : Dorsomedial nucleus of the posterior thalamus DSD : Decussatio supraoptica dorsalis E : Entopallium FA : Fractional anisotropy FC : Fiber-bundle cross-section FD : Fiber density FOD : Fiber orientation distribution FPL : Fasciculus prosencephali lateralis / lateral forebrain bundle GP : Globus pallidus HA : Hyperpallium apicale / apical part of the hyperpallium HD : Hyperpallium densocellulare / densocellular part of the hyperpallium HVC : Used as a proper name (High vocal center) LAD : Lamina arcopallialis dorsalis / dorsal arcopallial lamina LaM : Lamina mesopallialis / mesopallial lamina LFM : Lamina frontalis suprema / supreme frontal lamina LFS : Lamina frontalis superior / superior frontal lamina LMAN : Nucleus lateralis magnocellularis nidopallii anterioris / lateral magnocellular nucleus of the anterior nidopallium LPS : Lamina pallio-subpallialis / pallial-subpallial lamina LSt : Striatum laterale / lateral striatum M : Mesopallium MD : Mean diffusivity MLD-DM-ICO : Intercollicular nucleus complex MMAN : Nucleus medialis magnocellularis nidopallii anterioris / medial magnocellular nucleus of the anterior nidopallium MRI : Magnetic Resonance Imaging MSt : Striatum mediale / medial striatum N : Nidopallium NCM : Nidopallium caudomediale / caudomedial nidopallium OM : Tractus occipito-mesencephalicus / occipito-mesencephalic tract Ov : Nucleus ovoidalis POA : Area praeoptica / pre-optic area Pt : Nucleus pretectalis / pretectal nucleus RA : Nucleus robustus arcopallialis / robust nucleus of arcopallium RARE : Rapid acquisition with relaxation enhancement RD : Radial diffusivity Rt : Nucleus rotundus surr : surroundings TeO : Tectum opticum / optic tectum tFA : Tractus fronto-arcopallialis / fronto-arcopallial tract TFM : Tractus thalamo-frontalis TnA : Nucleus taeniae amygdalae / nucleus taeniae of the amygdala TrO : Tractus opticus / optic tract TSM : Tractus septopallio-mesencephalicus / septopallio-mesencephalic tract