Research on language and aging typically shows that language comprehension is preserved across the life span. Recent neuroimaging results suggest that this good performance is underpinned by age-related neural reorganization [e.g., Tyler, L. K., Shafto, M. A., Randall, B., Wright, P., Marslen-Wilson, W. D., & Stamatakis, E. A. Preserving syntactic processing across the adult life span: The modulation of the frontotemporal language system in the context of age-related atrophy. Cerebral Cortex, 20, 352–364, 2010]. The current study examines how age-related reorganization affects the balance between component linguistic processes by manipulating semantic and phonological factors during spoken word recognition in younger and older adults. Participants in an fMRI study performed an auditory lexical decision task where words varied in their phonological and semantic properties as measured by degree of phonological competition and imageability. Older adults had a preserved lexicality effect, but compared with younger people, their behavioral sensitivity to phonological competition was reduced, as was competition-related activity in left inferior frontal gyrus. This was accompanied by increases in behavioral sensitivity to imageability and imageability-related activity in left middle temporal gyrus. These results support previous findings that neural compensation underpins preserved comprehension in aging and demonstrate that neural reorganization can affect the balance between semantic and phonological processing.

A common complaint of normal aging is the increase in word-finding failures such as tip-of-the-tongue states (TOTs). Behavioral research identifies TOTs as phonological retrieval failures, and recent findings [Shafto, M. A., Burke, D. M., Stamatakis, E. A., Tam, P., & Tyler, L. K. On the tip-of-the-tongue: Neural correlates of increased word-finding failures in normal aging. Journal of Cognitive Neuroscience, 19, 2060–2070, 2007] link age-related increases in TOTs to atrophy in left insula, a region implicated in phonological production. Here, younger and older adults performed a picture naming task in the fMRI scanner. During successful naming, left insula activity was not affected by age or gray matter integrity. Age differences only emerged during TOTs, with younger but not older adults generating a “boost” of activity during TOTs compared to successful naming. Older adults also had less activity than younger adults during TOTs compared to “don't know” responses, and across all participants, less TOT activity was affiliated with lower gray matter density. For older adults, lower levels of activity during TOTs accompanied higher TOT rates, supporting the role of an age-related neural mechanism impacting older more than younger adults. Results support a neural account of word retrieval in old age wherein, despite widespread age-related atrophy, word production processes are not universally impacted by age. However, atrophy undermines older adults' ability to modulate neural responses needed to overcome retrieval failures.

Here we address the contentious issue of how nouns and verbs are represented in the brain. The co-occurrence of noun and verb deficits with damage to different neural regions has led to the view that they are differentially represented in the brain. Recent neuroimaging evidence and inconsistent lesion–behavior associations challenge this view. We have suggested that nouns and verbs are not differentially represented in the brain, but that different patterns of neural activity are triggered by the different linguistic functions carried by nouns and verbs. We test these claims in a functional magnetic resonance imaging study using homophones—words which function grammatically as nouns or verbs but have the same form and meaning—ensuring that any neural differences reflect differences in grammatical function. Words were presented as single stems and in phrases in which each homophone was preceded by an article to create a noun phrase (NP) or a pronoun to create a verb phrase (VP), thus establishing the word's functional linguistic role. Activity for single-word homophones was not modulated by their frequency of usage as a noun or verb. In contrast, homophones marked as verbs by appearing in VPs elicited greater activity in the left posterior middle temporal gyrus (LpMTG) compared to homophones marked as nouns by occurring in NPs. Neuropsychological patients with grammatical deficits had lesions which overlapped with the greater LpMTG activity found for VPs. These results suggest that nouns and verbs do not invariably activate different neural regions; rather, differential cortical activity depends on the extent to which their different grammatical functions are engaged.

Neuropsychological impairments of English past tense processing inform a key debate in cognitive neuroscience concerning the nature of mental mechanisms. Dual-route accounts claim that regular past tense comprehension deficits reflect a specific impairment of morphological decomposition (e.g., jump + ed), disrupting the automatic comprehension of word meaning accessed via the verb stem (e.g., jump). Single-mechanism accounts claim that the deficits reflect a general phonological impairment that affects perception of regular past tense offsets but which might preserve normal activation of verb semantics. We tested four patients with regular past tense deficits and matched controls, using a paired auditory semantic priming/lexical decision task with three conditions: uninflected verbs (hope/wish), regular past tense primes (blamed/accuse), and irregular past tense primes (shook/tremble). Both groups showed significant priming for verbs with simple morphophonology (uninflected verbs and irregular past tenses) but the patients showed no priming for verbs with complex morphophonology (regular past tenses) in contrast to controls. The findings suggest that the patients are delayed in activating the meaning of verbs if a regular past tense affix is appended, consistent with a dual-route account of their deficit.

How objects are represented and processed in the brain is a central topic in cognitive neuroscience. Previous studies have shown that knowledge of objects is represented in a featurebased distributed neural system primarily involving occipital and temporal cortical regions. Research with nonhuman primates suggest that these features are structured in a hierarchical system with posterior neurons in the inferior temporal cortex representing simple features and anterior neurons in the perirhinal cortex representing complex conjunctions of features (Bussey & Saksida, 2002; Murray & Bussey, 1999). On this account, the perirhinal cortex plays a crucial role in object identification by integrating information from different sensory systems into more complex polymodal feature conjunctions. We tested the implications of these claims for human object processing in an event-related fMRI study in which we presented colored pictures of common objects for 19 subjects to name at two levels of specificity-basic and domain. We reasoned that domain-level naming requires access to a coarsergrained representation of objects, thus involving only posterior regions of the inferior temporal cortex. In contrast, basic-level naming requires finer-grained discrimination to differentiate between similar objects, and thus should involve anterior temporal regions, including the perirhinal cortex. We found that object processing always activated the fusiform gyrus bilaterally, irrespective of the task, whereas the perirhinal cortex was only activated when the task required finer-grained discriminations. These results suggest that the same kind of hierarchical structure, which has been proposed for object processing in the monkey temporal cortex, functions in the human.