Abstract
In a previous study (Andersen 1959, 1960 b) the interhippocampal fibre activity was found to be represented by an initial diphasic spike of the response of the field CA3 to contralateral symmetrical stimulation. Since all the interhippocampal fibres are thin (around 1 μ) and myelinated, it was felt that this tract might serve as a suitable structure for a study of the properties of thin fibres within the central nervous system. A correlation has been made between various functional and structural properties of the interhippocampal fibres. The results obtained in cat, rabbit and rat have been compared.