Changes in language functions during normal aging are greater for phonological compared with semantic processes. To investigate the behavioral and neural basis for these age-related differences, we used fMRI to examine younger and older adults who made semantic and phonological decisions about pictures. The behavioral performance of older adults was less accurate and less efficient than younger adults' in the phonological task but did not differ in the semantic task. In the fMRI analyses, the semantic task activated left-hemisphere language regions, and the phonological task activated bilateral cingulate and ventral precuneus. Age-related effects were widespread throughout the brain and most often expressed as greater activation for older adults. Activation was greater for younger compared with older adults in ventral brain regions involved in visual and object processing. Although there was not a significant Age × Condition interaction in the whole-brain fMRI results, correlations examining the relationship between behavior and fMRI activation were stronger for younger compared with older adults. Our results suggest that the relationship between behavior and neural activation declines with age, and this may underlie some of the observed declines in performance.

Tip-of-the-tongue (TOT) experiences are frustrating word-finding failures where people are temporarily unable to produce a word they are certain they know. TOT frequency increases with normal aging during adulthood, and behavioral evidence suggests that the underlying deficit is in retrieving the complete phonology of the target word during production. The present study investigated the neural correlates of this phonological retrieval deficit. We obtained 3-D T1-weighted structural magnetic resonance images (MRI) for healthy participants between 19 and 88 years old and used voxel-based morphometry to measure gray matter density throughout the brain. In a separate session, participants named celebrities cued by pictures and descriptions, indicating when they had a TOT, and also completed Raven's Progressive Matrices (RPM), a task that does not involve phonological production. The number of TOTs increased with age and also with gray matter atrophy in the left insula, an area implicated in phonological production. The relation between TOTs and left insula atrophy cannot be attributed to the correlation of each variable with age because TOTs were related to insula atrophy even with age effects removed. Moreover, errors on the RPM increased with age, but performance did not correlate with gray matter density in the insula. These results provide, for the first time, an association between a region in the neural language system and the rise in age-related word-finding failures and suggest that age-related atrophy in neural regions important for phonological production may contribute to age-related word production failures.

Three studies tested the claim that H.M. exhibits a fipure memory deficitfl that has left his ability to comprehend language unimpaired relative to memory-normal controls. In Study 1, H.M. and memory-normal controls of comparable intelligence, education, and age indicated whether sentences were ambiguous or unambiguous, and H.M. detected ambiguities significantly less often than controls. In Study 2, participants identified the two meanings of visually presented sentences that they knew were ambiguous, and relative to controls, H.M. rarely discovered the ambiguities without help and had difficulty understanding the first meanings, experimenter requests, and his own output. Study 3 replicated these results and showed that they were not due to brain damage per se or to cohort effects: Unlike H.M., a patient with bilateral frontal lobe damage detected the ambiguities as readily as young and same-cohort older controls. These results bear on two general classes of theories in use within a wide range of neurosciences and cognitive sciences: The data favor fidistributed-memory theoriesfl that ascribe H.M.'s deficit to semantic-level binding processes that are inherent to both language comprehension and memory, over fistages-of-processing theories, fl where H.M.'s defective storage processes have no effect on language comprehension.