Motor hemiplegia and the cerebral organization of movement in man: II. The myth of the human extrapyramidal system

Abstract

SUMMARY -Following a brief review of the concept of extrapyramidal system, clinical and anatomic evidence is presented against its relative prominence in man. It is proposed that the greatest part of those structures traditionally labeled as extrapyramidal effects its respective functional activities by way of the pyramidal tracts themselves.Such structures, centered around the basal nuclei, the cerebellum and possibly, the limbic areas of the prosencephalon are, according to the present suggestion, indeed, pre pyramidal. This model is based upon the clinical analysis of patients and agrees with more than one century of anatomic verifications in human brains, favoring the notion of the singularity of the human brain. Hemiplegia motora e organização cerebral do movimento no homem: II. O mito do sistema extrapiramidal humanoRESUMO -Após revisão sumária do conceito de sistema extrapiramidal, são apresentadas evidências clínicas e anatômicas contra sua importância relativa no homem.Propõe-se que as estruturas tradicionalmente agrupadas sob o rótulo extrapiramidal efetuem a maior parte de suas atividades funcionais, respectivamente, por intermédio dos próprios feixes piramidais. Tais estruturas -centradas nos núcleos da base dos hemisférios cerebrais, no cerebelo e, possivelmente, também, nas áreas límbicas do prosencéfalo -, de acordo com nossa proposição são, na verdade pre-piramidais.Esse modelo se baseia na análise clínica de pacientes, está de acordo com mais de um século de verificações anatômicas em cérebros humanos e, depõe a favor da noção de singularidade do cérebro humano.Anatomical and functional reorganization in the human brain --Contrary to the pyramidal system concept 1^ which evolved in daily clinical practice, the concept of the 'extrapyramidal system' (EPS) was coined by Prus at a physiology laboratory in 18981-24.He investigated the means by which cortically induced epilepsy spread down to segmental levels.Working on dogs, Prus realized that the convulsions would not be affected by bilateral transections of the pyramidal tracts (PTs) at either mesencephalic or pontine levels, which led to the conclusion that epileptic volleys could be transmitted caudally through pathways distinct from the PTs. These, he proposed to call "extrapyramidal" It is noteworthy that Prus believed such EP pathways to follow a sequential multisynaptic course from the cerebral cortex to the spinal cord, due to a number of interruptions in subcortical and brainstem stations.He also suggested that such tracts would be responsible for the 'coordination and association' of movements. Contemporary studies have confirmed and extended Prus' views by showing the anatomical organization of the cortico-reticulospinal tracts 132 a n d their crucial role in the propagation of cortical epilepsy to the segmental apparatus 149} * Serviço de Neurologia (Prof. H. Alvarenga), Hospital Universitário Gaffrée e Guinle, Rio de Janeiro. Rua GeneralBelford 226 -20961 Rio de Janeiro RJ -Brasil as well as in the integration of body axis balance duri...

The Clinicoanatomic Uniqueness of the Human Pyramidal Tract and Syndrome

“…Firstly, when the pyramidal tracts are bilaterally damaged in the cerebral hemispheres or brainstem the syndrome of double (or bilateral) hemiplegia ensues. Indeed, severe and complete bilateral hemiplegia equals the lockedin syndrome 1 ; secondly, contrary to prevailing knowledge 2 , associated damage to extrapyramidal structures is irrelevant for the production of the full syndrome of spastic hemiplegia in man. For the purposes of the present review, the pyramidal tract is defined by the collection of fibers that originate in the cerebral cortex and pass through the medullary pyramids without interruption in their way to the motor neuron pools of the spinal cord 3 .…”

Repetitive transcranial magnetic stimulation modulates cortical–subcortical connectivity in sensorimotor network

“…The cerebellum is also an important part of the extrapyramidal system and communicates with the cerebrum via two‐stage feedforward and feedback systems, the cortico‐ponto‐cerebellar pathway (i.e., the afferent pathway) and the cerebello‐thalamic‐cortical pathway (i.e., the efferent pathway) (de Oliveira‐Souza & Tovar‐Moll, 2012; Oliveira‐Souza, 1989; Stoodley & Schmahmann, 2010; Zaretsky, 1982). The cortico‐ponto‐cerebellar pathway originated from the cerebral cortical regions, terminated at the pons and then sends information to the cerebellar, whereas the cerebello‐thalamic‐cortical pathway originated from the cerebellar cortex, passing through the deep cerebellar nuclei, terminated at the THA and finally projected to the cerebrum cortex (Stoodley & Schmahmann, 2010).…”

The human extrapyramidal system

“…This definition leaves out the common assumptions that movement disorders, such as chorea and parkinsonism, are disorders of the extrapyramidal system, or that the basal ganglia and related pathways are part of the extrapyramidal system. No matter how well these assumptions may hold true for nonhuman species in general I will attempt to show that they entirely fail when applied to the human nervous system [8,9].…”