Structure of human auditory cortex. II. Axon distributions and morphological correlates of speech perception

In Golgi-impregnated specimens of human auditory cortex banding patterns of cortical afferents have been found. Viewed sagitally they are vertical columns with components in layers III, IV, VI and sometimes V. Viewed tangentially they are winding stripes roughly parallel to the gyral axis and of variable width (usually a few hundred micrometers). Although it is not possible to determine it in such sections, they are probably - by analogy with animal experiments - of callosal and/or thalamic origin. Also found were narrow radial bundles, also of indefinite origin. Relative densities of impregnated axons were higher in the columns than between them; also, the tangential orientation component was accentuated within the columns. These findings, together with those of the previous paper, are related to neurolinguistic discoveries. Possible morphological correlates are discussed for neurolinguistic phenomena such as parallel processing of phonemes and words and unilateral, categorical perception of consonants compared with bilateral recognition of vowels and continuous transitions between them.