NMR IN BIOMEDICINE NMR Biomed. 2006;19:18–29 Published online 12 January 2006 in Wiley InterScience (www.interscience.wiley.com). DOI:10.1002/nbm.989 IR-SE and IR-MEMRI allow in vivo visualization of oscine neuroarchitecture including the main forebrain regions of the song control system Ilse Tindemans, Tiny Boumans, Marleen Verhoye and Annemie Van der Linden* Bio-Imaging Lab, Biomedical Sciences, University of Antwerp, Antwerp, Belgium Received 2 May 2005; Revised 5 August 2005; Accepted 5 August 2005 ABSTRACT: Songbirds share with humans the capacity to produce learned vocalizations (song). Recently, two major regions within the songbird’s neural substrate for song learning and production; nucleus robustus arcopallii (RA) and area X (X) are visualized in vivo using Manganese Enhanced MRI (MEMRI). The aim of this study is to extend this to all main interconnected forebrain Song Control Nuclei. The ipsilateral feedback circuits allow Mn 2þ to reach all main Song Control Nuclei after stereotaxic injection of very small doses of MnCl 2 (10 nl of 10 mM) into HVC of one and MAN (nucleus magnocellularis nidopallii anterioris) of the other hemisphere. Application of a high resolution (80 m) Spin Echo Inversion Recovery sequence instead of conventional T1-weighted Spin Echo images improves the image contrast dramatically such that some Song Control Nuclei, ventricles, several laminae, fibre tracts and other specific brain regions can be discerned. The combination of this contrast-rich IR-SE sequence with the transsynaptic transport property of Manganese (Inversion Recovery based MEMRI (IR-MEMRI)) enables the visualization of all main interconnected components of the Song Control System in telencephalon and thalamus. Copyright # 2006 John Wiley & Sons, Ltd. KEYWORDS: manganese-enhanced MRI; inversion–recovery; song control system; oscine brain INTRODUCTION The song control system (SCS) of songbirds, a bilateral circuit of distinct, strongly ipsilaterally interconnected brain regions, is an excellent model to study the neural substrate of a complex learned behaviour (singing). It displays a remarkable neuroplasticity which has been extensively analyzed (1–4). The SCS involves two functionally distinct, mainly telencephalic circuits (Fig. 1). The ‘motor pathway’ gua- rantees normal song production and includes HVC and the nucleus robustus arcopallii (RA), which innervates the vocal motor nucleus in the medulla (XIIts) and the premotor nuclei regulating respiration during song (5). The ‘anterior forebrain pathway’ (AFP) also links HVC to RA via a projection from HVC to area X in the medial striatum (MSt), which innervates the dorsal thalamic nucleus DLM. In turn, DLM projects back upon the lateral part of the nucleus magnocellularis nidopallii anterioris (LMAN), which finally projects upon RA, thereby linking the two parts of song control circuitry within the forebrain. The AFP seems to be essential for song learning and although it is interconnected with the motor pathway, it is not required for normal adult song production (6). In addition to these main parts of the SCS there are several diencephalic nuclei associated with the SCS, the functions of which are poorly understood. One Copyright # 2006 John Wiley & Sons, Ltd. NMR Biomed. 2006;19:18–29 *Correspondence to: A. van der Linden, Bio-Imaging Lab, University of Antwerp, Groenenborgerlaan 171, B-2020 Antwerp, Belgium. E-mail: annemie.vanderlinden@ua.ac.be Contract/grant sponsor: University of Antwerp, Concerted Research Actions (GOA funding). Contract/grant sponsor: National Science Foundation (FWO); Contract/grant number: G.0420.02. Abbreviations used: A, arcopallium; AD, arcopallium dorsale; AFP, anterior forebrain pathway; AVG, average; Bas, nucleus basorostralis pallii; BBB, blood–brain barrier; BOLD, blood oxygenation level- dependent; Cb, cerebellum; CNR, contrast-to-noise ratio; CO, chiasma opticum; CoA, commisura anterior; CoP, commisura posterior; DLM, nucleus dorsolateralis anterior, pars medialis; DMP, nucleus dorsome- dialis posterior thalami; dNCL, dorsal part of the nidopallium caudo- laterale; DTI, diffusion tensor imaging; E, entopallium; EPI, echo planar imaging; FA, tractus fronto-arcopallialis; FOV, field of view; FPL, lateral forebrain bundle; GE, gradient echo; GP, globus pallidus; HA, hyperpallium apicale; Hp, hippocampus; ICo, nucleus intercolli- cularis; IR, inversion–recovery; IR-MEMRI, inversion–recovery-based MEMRI; L, field L; LAD, lamina arcopallialis dorsalis; LaM, lamina mesopallialis; LM, lentiformis mesencephali; LMAN, lateral part of MAN; LPS, lamina pallio-subpallialis; LSt, lateral striatum; M, me- sopallium; MAN, nucleus magnocellularis nidopallii anterioris; MEMRI, manganese-enhanced magnetic resonance imaging; MLd, nucleus mesencephalicus lateralis pars dorsalis; MMAN, medial part of MAN; Mn 2þ , manganese; MSt, medial striatum; N, nidopallium; NIf, nucleus interfacialis nidopalii; nSt, nucleus striaterminalis; nXII, hypoglossal nucleus; OM, tractus occipito-mesencephalicus; Ov, nu- cleus ovoidalis; POM, nucleus preopticus medialis; QF, tractus quinto- frontalis; RA, nucleus robustus arcopallii; Rt, nucleus rotundus; SCN, song control nuclei; SCS, song control system; SE, spin echo; SI, signal intensity; SNR, signal-to-noise ratio; SSp, nucleus supraspina- lis; T1W, T 1 -weighted; TeO, tectum opticum; TFM, tractus thalamo- frontalis et frontalis-thalamicus medialis; TI, inversion time; Tn, nucleus taniae; TrO, tractus opticus; TSM, tractus septopallio-mesen- cephalicus; Uva, nucleus uvaeformis; X, area X; XIIts, tracheosyrin- geal part of the hypoglossal nucleus.