Functional Role of Auditory Cortex in Frequency Processing and Pitch Perception

Abstract

. Microelectrode studies in nonhuman primates and other mammals have demonstrated that many neurons in auditory cortex are excited by pure tone stimulation only when the tone's frequency lies within a narrow range of the audible spectrum. However, the effects of auditory cortex lesions in animals and humans have been interpreted as evidence against the notion that neuronal frequency selectivity is functionally relevant to frequency discrimination. Here we report psychophysical and anatomical evidence in favor of the hypothesis that fine-grained frequency resolution at the perceptual level relies on neuronal frequency selectivity in auditory cortex. An adaptive procedure was used to measure difference thresholds for pure tone frequency discrimination in five humans with focal brain lesions and eight normal controls. Only the patient with bilateral lesions of primary auditory cortex and surrounding areas showed markedly elevated frequency difference thresholds: Weber fractions for frequency direction discrimination ("higher"-"lower" pitch judgments) were about eightfold higher than Weber fractions measured in patients with unilateral lesions of auditory cortex, auditory midbrain, or dorsolateral frontal cortex; Weber fractions for frequency change discrimination ("same"-"different" pitch judgments) were about seven times higher. In contrast, pure-tone detection thresholds, difference thresholds for pure tone duration discrimination centered at 500 ms, difference thresholds for vibrotactile intensity discrimination, and judgments of visual line orientation were within normal limits or only mildly impaired following bilateral auditory cortex lesions. In light of current knowledge about the physiology and anatomy of primate auditory cortex and a review of previous lesion studies, we interpret the present results as evidence that fine-grained frequency processing at the perceptual level relies on the integrity of finely tuned neurons in auditory cortex. I N T R O D U C T I O NMany neurons in mammalian auditory cortex respond selectively to pure tone frequencies over a narrow range of the audible spectrum, and several anatomical subdivisions of auditory cortex are organized topographically with respect to frequency selectivity (for reviews, see Aitkin et al. 1984;Brugge and Reale 1985;Clarey et al. 1992;de Ribaupierre 1997;Kaas et al. 1999;Phillips et al. 1991;Schreiner 1992). On theoretical grounds, it would seem reasonable to propose that neuronal frequency selectivity at the physiological level contributes to frequency discrimination at the perceptual level. However, the functional effects of auditory cortex lesions in animals and humans have been interpreted as evidence against this hypothesis. In their authoritative review of a large number of lesion studies in the Handbook of Sensory Physiology, Neff et al. (1975) concluded, "Frequency discrimination may be learned or relearned after bilateral lesions involving all or nearly all of primary auditory cortex in animals such as the cat and monkey and in human patient...

Hearing suppression induced by electrical stimulation of human auditory cortex

“…It is possible that disruption of local cortical activity alone could suppress hearing, although it is generally agreed that in humans (Tramo et al, 2002;Kaga et al, 2000;Hausler and Levine, 2000;Penfield and Perot, 1963) and in laboratory animals (Heffner and Heffner, 1986;Heffner, 1997;Colombo et al,1996;Whitfield et al, 1978) that unilateral destruction of auditory cortex of the STG does not result in deafness. More likely, hearing suppression is the result of activating corticofugal efferent pathways that project to auditory thalamic, midbrain and brainstem structures, and possibly the cochlea (Hazama et al, 2004;He, 2003;Jacomme et al, 2003, Suga andPandya et al, 1994;Weedman and Ryugo, 1996a,b).…”

Towards a neural basis of music perception

“…Diese Strukturen sind entscheidend in emotionale Prozesse (Amygdala), in die Evaluation sensorischer Information (Orbitofrontalkortex) und in die Kontrolle emotionalen Verhaltens (ebenfalls Orbitofrontalkortex) involviert. Im auditorischen Kortex (höchstwahrscheinlich sowohl in primären als auch in angrenzenden sekundären auditorischen Feldern) werden akustische Merkmale wie Tonhöhe, Tonchroma, Klangfarbe, Intensität und Rauhigkeit extrahiert 1 (Tramo et al, 2002;Patel & Balaban, 2001;Schönwiesner et al, 2002;Warren et al , 2003;Fishman et al, 2001). Die diesen Extraktionen zugrundeliegenden Operationen sind elektrisch vermutlich in sog.…”

Cortical representations of pitch in monkeys and humans

“…In cats, bilateral lesions of the entire auditory cortex impair the discrimination of changes in the pitch of the missing fundamental, but not changes in frequency alone, demonstrating the necessity of auditory cortex in pitch perception [46]. Humans with partial auditory cortex lesions have also been shown to have poorer pitch discrimination [47], with lesions of the right auditory cortex showing larger deficits [48][49]. Behavioral studies in patients with auditory cortex lesions have further suggested that lesions anterior to primary auditory cortex result in more pronounced deficits in pitch discrimination [49].…”