title: The anatomy of fronto-occipital connections from early blunt dissections to contemporary tractography.
abstract: The occipital and frontal lobes are anatomically distant yet functionally highly integrated to generate some of the most complex behaviour. A series of long associative fibres, such as the fronto-occipital networks, mediate this integration via rapid feed-forward propagation of visual input to anterior frontal regions and direct top-down modulation of early visual processing. Despite the vast number of anatomical investigations a general consensus on the anatomy of fronto-occipital connections is not forthcoming. For example, in the monkey the existence of a human equivalent of the 'inferior fronto-occipital fasciculus' (iFOF) has not been demonstrated. Conversely, a 'superior fronto-occipital fasciculus' (sFOF), also referred to as 'subcallosal bundle' by some authors, is reported in monkey axonal tracing studies but not in human dissections. In this study our aim is twofold. First, we use diffusion tractography to delineate the in vivo anatomy of the sFOF and the iFOF in 30 healthy subjects and three acallosal brains. Second, we provide a comprehensive review of the post-mortem and neuroimaging studies of the fronto-occipital connections published over the last two centuries, together with the first integral translation of Onufrowicz's original description of a human fronto-occipital fasciculus (1887) and Muratoff's report of the 'subcallosal bundle' in animals (1893). Our tractography dissections suggest that in the human brain (i) the iFOF is a bilateral association pathway connecting ventro-medial occipital cortex to orbital and polar frontal cortex, (ii) the sFOF overlaps with branches of the superior longitudinal fasciculus (SLF) and probably represents an 'occipital extension' of the SLF, (iii) the subcallosal bundle of Muratoff is probably a complex tract encompassing ascending thalamo-frontal and descending fronto-caudate connections and is therefore a projection rather than an associative tract. In conclusion, our experimental findings and review of the literature suggest that a ventral pathway in humans, namely the iFOF, mediates a direct communication between occipital and frontal lobes. Whether the iFOF represents a unique human pathway awaits further ad hoc investigations in animals.
authors.affiliation: NATBRAINLAB, Department of Forensics and Neurodevelopmental Sciences, King's College London, Institute of Psychiatry, UK; Department of Neuroimaging Sciences, King's College London, Institute of Psychiatry, UK. Electronic address: stephanie.forkel@gmx.net.
authors.forename: Stephanie J
authors.initials: SJ
authors.lastname: Forkel
authors.affiliation: NATBRAINLAB, Department of Forensics and Neurodevelopmental Sciences, King's College London, Institute of Psychiatry, UK; Inserm - UPMC UMRS 975, Brain and Spine Institute, Groupe Hospitalier Pitié-Salpêtrière, Paris, France.
authors.forename: Michel
authors.initials: M
authors.lastname: Thiebaut de Schotten
authors.affiliation: NATBRAINLAB, Department of Forensics and Neurodevelopmental Sciences, King's College London, Institute of Psychiatry, UK.
authors.forename: Jamie M
authors.initials: JM
authors.lastname: Kawadler
authors.affiliation: Department of Neuroimaging Sciences, King's College London, Institute of Psychiatry, UK; NIHR Biomedical Research Centre for Mental Health at South London and Maudsley NHS Foundation Trust and Institute of Psychiatry, King's College London, UK.
authors.forename: Flavio
authors.initials: F
authors.lastname: Dell'Acqua
authors.affiliation: Neurology Department, Ludwig-Maximilians-Universität Munich, Germany.
authors.forename: Adrian
authors.initials: A
authors.lastname: Danek
authors.affiliation: NATBRAINLAB, Department of Forensics and Neurodevelopmental Sciences, King's College London, Institute of Psychiatry, UK.
authors.forename: Marco
authors.initials: M
authors.lastname: Catani
mesh_terms: D001931:Brain Mapping / Q000266:history* / Q000379:methods; D004210:Dissection / Q000266:history* / Q000379:methods; D005625:Frontal Lobe / Q000033:anatomy & histology*; D049672:History, 19th Century; D049673:History, 20th Century; D049674:History, 21st Century; D006801:Humans; D009434:Neural Pathways / Q000033:anatomy & histology; D059906:Neuroimaging / Q000266:history* / Q000379:methods; D009778:Occipital Lobe / Q000033:anatomy & histology*
keywords: Agenesis of the corpus callosum; Diffusion MRI; Fronto-occipital fasciculus; Neuroanatomy; Tractography; White matter