On the structure and functional relations of the optic thalamus. By Ernest Sachs, A.B., MD, of New York. From Sir Victor Horsley's Laboratory, Department of Pathological Chemistry, University College, London. Brain 1909: 32; 95–186.
Cambridge
Acknowledging the roles of Sir Victor Horsley and Dr R.H. Clarke in suggesting the study and providing the necessary apparatus (see Brain 2007: 130; 1449–1452), Dr Sachs starts with an historical account of what is currently known concerning the anatomy and physiology of the thalamus, leaning much on the historical account by Gustave Roussy (La couche optique, 1907). Prior to the pioneering work of Hermann Nothnagel (1874), who first lesioned the thalamus with fluid, discrete but crude areas of damage were created by mechanical probes and electrolytic lesions. This work displaced the erroneous idea dating from Francois Magendie (La système nerveux, 1841) that the thalamus is the motor centre to one placing this ganglion as the unconscious reflex centre that relays stimuli from the periphery to form motor images that are the basis for voluntary action. Gradually, through a series of claims (dubious and more plausible), was built up an impressive catalogue of brain functions in which the thalamus plays a role—motor, sensory, autonomic, visual, auditory and behavioural (including a ‘screaming centre’, described by Vladimir Bechterew as ‘Geschrei wie es auf Schmerz auftritt’). Others defined thalamic anatomy but could not agree on the number of nuclei, each having discrete connections with parts of the cortex. Notwithstanding the authority of Constantin von Monakow (1895), Heinrich Obersteiner (1901), Santiago Ramon y Cajal (1902) and Otto Marburg (1904), after spending time in Vienna with Professor Obersteiner and, with help from Horsley, Dr Sachs proposes a classification of seven main thalamic nuclei (anterior, medial, lateral, ventral, centre median, arcuate and pulvinar). Now, he rehearses the state of knowledge concerning connectivities: thalamo-cortical, cortico-thalamic, thalamo-striate and a variety of descending thalamo-fugal projections to the brain stem and medulla but no further. But there is work yet to be done in reconciling the true number of thalamic nuclei, their cortical connections and the existence of thalamic efferents to other structures. Sensing that his readers may skip details of the next 80 pages of methods and results, Dr Sachs explains that he will endorse the position originally suggested by Friedrich Burdach in 1819 and conclude that the thalamus consists of three parts: an external structure placed between the internal capsule and lamina interna; an internal part lying between that lamina and the midline; and an anterior nucleus.
His study is based on an analysis of 61 monkeys and 33 cats. With Sir Victor Horsley, he has: lesioned the cortex with nitric acid or galvano-cautery and studied the thalamus (18 animals; 9 cats and 10 monkeys [sic]) in whom observations could reliably be made (group I); lesioned the thalamus with electrolysis using the Clarke and Horsley stereotactic frame and studied the cortex (4 cats and 27 monkeys: group II); and excited the thalamus and neighbouring structures electrically using bipolar electrodes, observing voluntary movements and pupil reactions but ignoring any autonomic responses (group III). Obviously, Sachs has read the already famous Clarke and Horsley paper from 1908 and he rehearses the principles of stereotactic topography defined by coordinates from three planes based on external markings that map exact positions of the seven thalamic nuclei.
In group I, the principle of connections between cortex and thalamus is confirmed: anterior to anterior; middle to middle; and occipital to pulvinar. Here, there is no disagreement with contemporary anatomists except with respect to connectivities of the middle part of the thalamus. Those gyri occupying the pre- and post-central (better referred to as pre- and post-crucial, sigmoid, lateral and suprasylvius medius gyri) and neighbouring structures project, in the cat and monkey, both to the ventral and lateral thalamic nuclei—and with no difference depending on representation of the (Macaque) arm and leg—but nothing crosses the boundary of the internal lamina, which therefore acts as a strict demarcation zone. In passing, the existence is confirmed of fibres arising from suprasylvian and ectosylvian gyri of the temporal lobe that may pass through the thalamus but project directly to the tectum, stimulation of which results in movements of the eyes and ears. And Dr Sachs has no difficulty in persuading Sir Victor that his observations from 1900–1902 on the origin of tectal inputs from the motor cortex needs refinement. Specifically, it is connections between the gyrus cononialis and the colliculi that are involved in conjugate deviation of the head and eyes.
The direct stereotactic placement of electrolytic lesions in the thalamus allows Dr Sachs to chart local and more distant connections of each constituent part (see Figs 1 and 2). The anterior nucleus sends fibres mainly to the anterior and middle caudate, a few reaching the lateral caudate and others passing back to the median thalamic nucleus via the lamina interna. Thus (taken with other work), the anterior nucleus acts as a relay station that connects the mammillary bodies and the striatum. The median nucleus also projects to the caudate, its fibres traversing the lateral thalamic nucleus en route, where a few fibres may terminate; others connect internally with the nucleus reuniens of the thalamus that Dr Sachs had previously studied whilst working with Professor Obersteiner in Vienna. As for the lateral nucleus—having dorsal, middle and ventral portions—Ernest Sachs first considers a previous anatomical dispute to be settled by his studies: the fillet (medial lemniscus) and afferents from the superior cerebellar peduncle terminate here and project no further. But of more importance is the fact that, unlike the anterior and median nuclei, lesions of the lateral thalamic structure invariably result in degenerations that confirm the presence of cortical efferents from the thalamus organized with dorsal–ventral polarity and differentially distributed to the pre- and post-central gyri. Thus, the lateral nucleus observes strict topographic representation to cortical areas for the leg (dorsal), upper limb but with some overlap into the leg and face (middle), and face (ventral). At the microscopic level, there is also some relationship between these arrangements and the distribution of Betz cells in the motor cortex. The number of fibres projecting to the pre- and post-central gyrus and their diameters differ, the motor cortex receiving more and larger fibres than the post-central sensory cortex. In addition, there arises from the medial part of the lateral nucleus, fibres that connect with the medial part of the thalamus. Considering the centre median and arcuate nuclei as one, Dr Sachs is emphatic that their fibres project only within the thalamus itself, mainly to the lateral nucleus, and with no cortical or mesencephalic connections, although the closely placed posterior longitudinal bundle that originates from the ventral nucleus has efferent and afferent connections to various cranial nerve nuclei. It has not proved technically feasible for Dr Sachs selectively to lesion the pulvinar.
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Damage occurring around the thalamus helps to explain the relationships of some neighbouring structures especially the hypothalamus: the field of Forel sends efferents through the internal capsule to the globus pallidus but not the putamen; contributes to the bulk of fibres making up the ansa lenticularis; and connects with the red nucleus. In turn, that nucleus forms part of connections between the cerebellum and thalamus traversing the superior cerebellar peduncle, and projects caudally via the rubro-bulbar and rubro-spinal pathways; but there is no evidence for efferent connections from the thalamus to the red nucleus.
Direct thalamic stimulation without associated destructive lesions, studied by subsequent anatomical confirmation of the electrode placements (Fig. 3), shows that the anterior thalamic nucleus is not excitable, and nor is the dorsal part of the medial nucleus, whereas more medial stimulation of that structure results in attention, fixation of the eyes in the visual axis and pupillary dilatation. A little more ventral, stimulation and excitation of the median nucleus produces contralateral fore-limb flexion and deviation of the head and eyes. Broadly these are also the results of stimulating the lateral nucleus, although, the contralateral movement is usually fractionated depending on precisely where the electrode is placed. The centre median and arcuate nuclei yield ocular fixation and combinations of flexion and extension in the opposite forelimb. Pulvinar stimulation consistently produces ocular deviation to the opposite side and dilation of the pupils. Although noting any such effects, Dr Sachs is not much concerned with the symptomatic consequences of cortical and thalamic stimulation: ‘any thalamic syndrome must consist of an arrangement of disordered function of those senses whose special thalamic regions are destroyed, and of those tracts—e.g. the internal capsule, optic tract, etc.—which lie near’.
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So what has Dr Sachs learned on his European tour? The hypothalamus—connected to the globus pallidus—is very different from the thalamus. This should be considered as having an inner part (anterior and median nuclei) connected to the caudate and rhinencephalon: quite different is the outer part where the medial lemniscus and superior cerebellar peduncle terminate and topographically precise connections to the Rolandic region of the cortex arise.
Born in 1879, Dr Sachs later held the chair of neurological surgery in St Louis. He retired in 1949 and ‘Yale University was proud to invite him to become an honorary member of its faculty with assignment to the Department of Physiology. His paper on the functions of the thalamus, based on work that he had done in London with Horsley in 1909, was not forgotten’ (John Fulton, 1952). Dr Sachs died in 1958. The publication in Brain was identified by Fielding Garrison and Leslie Morton as significant in the history of medicine when their original listing appeared in 1943. That said, in the opinion of Alfred Meyer (Historical aspects of cerebral anatomy, 1971), clarification—at least for nuclei close to the midline—was not reached until FC Guardjian (1927) ‘distinguished the parataenialis, reuniens, rhomboidalis, paraventriculares anterior and posterior, centralis and nuclei commisurales inter-anterodorsalis and inter-anteromedialis’ thalamic nuclei; so, it seems, ‘plus ça change’. But as the opinions of John Kaas endorse (page 2470) and the work of Robert Ward and Isabel Arend reveal, not all is yet known about this ganglion placed in the dark basements of the brain and at the cross-roads of neural connections that orchestrate the integrative actions of the nervous system.
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