Among the most perplexing consequences of lesions to the left temporal lobe is the co-occurrence of two apparently unrelated deficits: a marked impairment in parsing the grammatical structure of spoken sentences, and a strikingly specific inability to distinguish between tones separated by less than a semitone. For decades, the prevailing view held that these deficits, however coincident in clinical presentation, were functionally independent — the result of a single lesion disrupting anatomically adjacent but computationally distinct circuits. That view became untenable with the advent of high-resolution tractography, which revealed that the fiber pathways subserving syntactic analysis and those mediating fine-grained pitch discrimination are not merely adjacent but are densely interwoven within a subregion of the left planum temporale.

This anatomical entanglement prompted researchers to hypothesize that the cognitive operations underlying grammatical parsing and those supporting pitch acuity are not merely co-localized but are neurologically coupled — that the brain, in effect, processes linguistic structure and musical pitch through a shared or deeply interdigitated computational architecture. Direct support for this hypothesis arrived with a 2019 investigation in which targeted electrical stimulation was applied to the interwoven region of the planum temporale while participants performed a battery of auditory tasks. The stimulation selectively disrupted both syntactic parsing and fine pitch discrimination, yet left other auditory capacities — such as the ability to recognize familiar voices or to localize sounds in space — entirely intact.

According to the passage, the tractography findings serve primarily to

A. reconcile two apparently contradictory clinical observations by demonstrating that they originate from a single neural substrate.
B. undermine a previously accepted account of the relationship between the two deficits.
C. establish that syntactic processing and pitch discrimination are localized in entirely separate regions of the temporal lobe.
D. call into question the reliability of diffusion imaging as a method for mapping neural pathways.
E. demonstrate that lesions to the planum temporale produce more severe syntactic deficits than pitch discrimination deficits.



The 2019 stimulation study is presented as

A. providing direct experimental confirmation of a hypothesis that anatomical evidence had already made plausible.
B. offering an alternative to tractography for investigating the functional architecture of the temporal lobe.
C. revealing that syntactic and musical abilities are mediated by computationally distinct neural circuits.
D. challenging the assumption that electrical stimulation can selectively target individual cognitive functions.
E. suggesting that the deficits first catalogued by Wernicke have a different underlying cause than was previously assumed.