Making sense out of jargon: A neurolinguistic and computational account of jargon aphasia

Objective: To identify the cognitive and neuroanatomic bases of neologistic jargon aphasia with spared comprehension and production of written words. Methods: Detailed analysis of performance across experiments of naming, reading, writing, repetition, and word/picture matching by a 68- year-old woman (J.B.N.) served to identify which cognitive mechanisms underlying naming and word comprehension were impaired. J.B.N.'s impairments were then simulated by selectively 'lesioning' a computer model of word production that has semantic, word form, and subword phonologic levels of representation (described by Dell in 1986). Results: In comprehension experiments, J.B.N. made far more errors with spoken word input than with written word or picture input (chi-square = 40-59; df = 1; p < 0.0001) despite intact auditory discrimination. In naming experiments (with picture, definition, or tactile input), J.B.N. made far more errors in spoken output relative to written output (chi-square = 14-56; df = 1; p < 0.0001). These selective impairments of spoken word processing were simulated by reducing connection strength between word-level and subword-level phonologic units but maintaining full connection strength between word-level and semantic units in Dell's model. The simulation yielded a distribution of error types that was nearly identical to that of J.B.N., and her CT and MRI scans showed a small subarachnoid hemorrhage in the left sylvian fissure without infarct. Cerebral angiogram showed focal vasospasm in sylvian branches of the left middle cerebral artery. Conclusion: Focal left perisylvian dysfunction can result in a highly selective 'disconnection' between word-level and subword-level phonologic representations manifest as neologistic jargon aphasia with intact understanding and production of written words.