In the interwar period, biologists employed a diverse set of holistic approaches that were connected to different research methodologies. Against this background, this article explores attempts in the 1920s and 1930s to negotiate quantitative and qualitative methods in the field of neurophysiology. It focuses on the work of two scientists on different sides of the Atlantic: the Dutch animal psychologist and physiologist Frederik J.J. Buytendijk and the American neuropsychologist Karl S. Lashley, specifically analyzing their critical correspondence, 1929–1932, on the problems (...) surrounding the term _intelligence._ It discusses the inexplicable anomalies in neurophysiology as well as the reliability of quantitative and qualitative methods. While in his laboratory work Lashley adhered to a strictly analytic approach, Buytendijk tried to combine quantitative methods with phenomenological and hermeneutical approaches. The starting point of their discussion is Lashley’s monograph on _Brain Mechanisms and Intelligence_ (1929) and the rat experiments discussed therein. Buytendijk questioned the viability of the maze-learning method and the use of statistics to test intelligence in animals; he reproduced Lashley’s experiments and then confronted Lashley with his critical findings. In addition to elucidating this exchange, this paper will, more generally, shed light on the nature of the disagreements and shared assumptions prevalent among interwar neurophysiologists. In turn, it contributes to historiographical debates on localization and functionalism and the discrepancy between analytic (quantitative) and interpretative (qualitative) approaches. (shrink)