Relations between thalamic and corticofrontal sites of oculomotor control in the cat.

Recent studies from this laboratory have attempted to delineate the thalamic 15 and frontal cortical 14 regions from which conjugate eye movements could be elicited by low-threshold electrical stimulation in cats. The existence of connections between these thalamic and cortical sites has been postulated on the basis of anatomical dataT,1L However, ditficulties of interpretation inherent in conventional anatomical methods when applied to this particular problem make the conclusions still disputableL This study presents orthodromic single cell responses obtained but unreported in previous experiments on direct projections from frontal cortex to the thalamus s. The data are reported here since they show functional connections between structures specified by their functional properties, and since they suggest a similar organization of thalamocortical connections for the frontal lobe of cat and primate. These experiments were performed on 20 enc6phale isol6 cats under local anesthesia. Stimulation (single pulses or 10 Hz trains of pulses of 100-500/zA and 0.5 msec duration) was applied through fine concentric electrodes (David Kopf NE-100) implanted (1) within the internal medullary lamina: nucleus centralis lateralis (CL), (2) medial to the lamina: nucleus medialis dorsalis (MD), or (3) immediately external to the lamina: nucleus ventralis lateralis (VL) or ventralis posterior (VP). The stimulating current was monitored and equalized. In all cases, the production of ocular movements by stimulation was tested, and it was verified that such movements (contraversive deviations) were obtained only from CL placements8,15. After this test, the animals were paralyzed with Flaxedil, and the cortical frontal lobe was explored with glass micropipettes filled with 3 M KCI (tip diameter of less than 2 #m). Recordings from 40 to 100 units were obtained in each experiment along 2 or 3 tracks through the proreal and anterior sigmoid gyri, both lips of the cruciate and presylvian sulci and the mesial face of the frontal lobe. The responsiveness of each cell to the thalamic stimulation sites listed above was determined. The positions of the units were com-

[1]  M. Murray.  Degeneration of some intralaminar thalamic nuclei after cortical removals in the cat , 1966, The Journal of comparative neurology.

[2]  K. Akert,et al.  Orbitofrontal cortical lesions and learning in cats , 1962, The Journal of comparative neurology.

[3]  J. Schlag,et al.  Thalamic incremental responses to prefrontal cortical stimulation in the cat. , 1970, Brain research.

[4]  K. Akert,et al.  Cortical area 8 and its thalamic projection in Macaca mulatta , 1963, The Journal of comparative neurology.

[5]  L. Smaha,et al.  Efferent projections of the nucleus ventralis lateralis. An experimental study in the cat. , 1969, Journal of anatomy.

[6]  P. Strick.  Cortical projections of the feline thalamic nucleus ventralis lateralis. , 1970, Brain research.

[7]  A. Scheibel,et al.  Structural organization of nonspecific thalamic nuclei and their projection toward cortex. , 1967, Brain research.

[8]  W. E. Clark,et al.  The Thalamic Connections of the Parietal and Frontal Lobes of the Brain in the Monkey , 1935 .

[9]  W. Waller.  Thalamic connections of the frontal cortex of the cat , 1940 .

[10]  W. R. Ingram,et al.  SOME EFFERENT CONNECTIONS OF THE NUCLEUS MEDIALIS DORSALIS. AN EXPERIMENTAL STUDY IN THE CAT. , 1965, The American journal of anatomy.

[11]  J Schlag,et al.  Direct projections from cat frontal eye field to internal medullary lamina of the thalamus. , 1971, Experimental neurology.

[12]  M. Schlag-Rey,et al.  Induction of oculomotor responses by electrical stimulation of the prefrontal cortex in the cat. , 1970, Brain research.

[13]  M. Schlag-Rey,et al.  Induction of oculomotor responses from thalamic internal medullary lamina in the cat. , 1971, Experimental neurology.

[14]  W. Cowan,et al.  The interpretation of the degenerative changes in the intralaminar nuclei of the thalamus. , 1967, Journal of neurology, neurosurgery, and psychiatry.

[15]  D. Albe-Fessard,et al.  Cortical projections of cat medial thalamic cells. , 1971, The International journal of neuroscience.