A Study of Thalamo-cortical Relations

The present study is a topographical analysis of thalamo-cortical relations as revealed by alterations in the electrocorticogram induced by localized thalamic stimulation. The work has been based upon the assumption that the complex spontaneous pattern of the cortex represents an aggregation of various sorts of activity, some of which might have separate anatomical substrates capable of more or less discrete activation. Evidence has already been presented (Morison, Dempsey and Morison, 1941b) for the existence of at least one such system (in that case extrathalamic). METHODS. Cats under various degrees of nembutal anesthesia (0.6 to 0.9 cc./ kgm.) were used. Both cortices were exposed and the stereotactic instrument described by Morison, Dempsey and Morison (1941a) applied to the skull. The stimulating electrodes consisted of two enameled stainless steel wires held in the barrel of a al-gauge hypodermic needle, the bared tips separated by a distance of about 1 mm. Arrangements for supplying stimulating current were similar to those described before (lot. cit.) except that a resistance of 10,000 ohms was inserted between the center tap of the Wagner balancing potentiometer and ground. Recording electrodes consisted either of silver wires arranged in pairs with an interpolar distance of 1 mm. or silver-silver chloride-Ringer-agar wicks making a somewhat diffuse contact with the pia (3-6 sq. mm.). When the wicks were used, records were usually taken between each of them and an " indifferent " one placed on the muscles of the neck. When the silver wires were employed, as was usually the case, similar " monopolar " recordings were taken between one of the members of the pair and an " indifferent " point. When responses appeared, changes were made by means of selector switches so that records were taken between the two members of a single pair. This is not the place to discuss the very important theoretical objections which may be advanced against the two methods of recording, but in general it may be said that the data assembled have been analyzed with two major considerations in mind. Absence of a response on a diffuse monopolar lead points to a lack of significant electrical activity in a relatively wide surrounding area, while presence of response recorded with bipolar electrodes indicates activity very near (less than a millimeter) to them. Conversely presence of activity on the monopolar or absence from the bipolar setting is of less significance. The recording instruments used were …