An fMRI investigation of the effects of attempted naming on word retrieval in aphasia

In healthy controls, picture naming performance can be facilitated by a single prior exposure to the same picture ("priming"). This priming phenomenon is utilized in the treatment of aphasia, which often includes repeated picture naming as part of a therapeutic task. The current study sought to determine whether single and/or multiple exposures facilitate subsequent naming in aphasia and whether such facilitatory effects act through normal priming mechanisms. A functional magnetic resonance imaging paradigm was employed to explore the beneficial effects of attempted naming in two individuals with aphasia and a control group. The timing and number of prior exposures was manipulated, with investigation of both short-term effects (single prior exposure over a period of minutes) and long-term effects (multiple presentations over a period of days). Following attempted naming, both short-term and long-term facilitated items showed improvement for controls, while only the long-term condition showed benefits at a behavioral level for the participants with aphasia. At a neural level, effects of long-term facilitation were noted in the left precuneus for one participant with aphasia, a result also identified for the equivalent contrast in controls. It appears that multiple attempts are required to improve naming performance in the presence of anomia and that for some individuals with aphasia the source of facilitation may be similar to unimpaired mechanisms engaged outside the language network

Priming Picture Naming with a Semantic Task: An fMRI Investigation

Prior semantic processing can enhance subsequent picture naming performance, yet the neurocognitive mechanisms underlying this effect and its longevity are unknown. This functional magnetic resonance imaging study examined whether different neurological mechanisms underlie short-term (within minutes) and long-term (within days) facilitation effects from a semantic task in healthy older adults. Both short- and long-term facilitated items were named significantly faster than unfacilitated items, with short-term items significantly faster than long-term items. Region of interest results identified decreased activity for long-term facilitated items compared to unfacilitated and short-term facilitated items in the mid-portion of the middle temporal gyrus, indicating lexical-semantic priming. Additionally, in the whole brain results, increased activity for short-term facilitated items was identified in regions previously linked to episodic memory and object recognition, including the right lingual gyrus (extending to the precuneus region) and the left inferior occipital gyrus (extending to the left fusiform region). These findings suggest that distinct neurocognitive mechanisms underlie short- and long-term facilitation of picture naming by a semantic task, with long-term effects driven by lexical-semantic priming and short-term effects by episodic memory and visual object recognition mechanisms

The neural correlates of picture naming facilitated by auditory repetition

Background: Overt repetition of auditorily presented words can facilitate picture naming performance in both unimpaired speakers and individuals with word retrieval difficulties, but the underlying neurocognitive mechanisms and longevity of such effects remain unclear. This study used functional magnetic resonance imaging to examine whether different neurological mechanisms underlie short-term (within minutes) and long-term (within days) facilitation effects from an auditory repetition task in healthy older adults

The neurocognitive substrates of naming facilitation in aphasia: An fMRI investigation.

Naming deficits are commonly experienced post-stroke and, given their high incidence and detrimental consequences, these impairments are frequently targeted in the treatment of aphasia. Evidence suggests that certain techniques can facilitate naming in aphasia, however, the neural mechanisms underpinning training-induced success remain unclear. This thesis aimed to advance our understanding of the mechanisms responsible for naming facilitation in the unimpaired brain and, importantly, to elucidate the neurocognitive substrates of naming facilitation in aphasia. Further, it aimed to determine whether such effects differ based on the type and timing of prior facilitation. The functional magnetic resonance imaging (fMRI) studies forming part of this thesis achieved these aims by utilizing two targeted language tasks that have been demonstrated to be effective facilitation techniques in individuals with aphasia. The level of processing required (either at the semantic or phonological level) in each language task was deliberately manipulated and allowed investigation of the potential locus of any positive effects upon subsequent naming performance. By manipulating the timing of prior facilitation using these tasks, either over the short-term (a period of minutes) or the long-term (a period of several days), the studies were also able to investigate the longevity of any facilitation effects. To our knowledge, no other neuroimaging studies have utilized this design to explore the underlying mechanisms involved in successful overt picture naming following facilitation, with targeted tasks over different timeframes, in individuals with aphasia and healthy controls. The thesis is comprised of four studies: semantic and phonological facilitation studies in both healthy individuals and in aphasia. The semantic studies investigated the behavioural and neurocognitive effects of naming facilitation using a semantic task in the absence of the phonological word form, and the time course of such effects. One experiment using this facilitation technique was conducted upon healthy controls and a second experiment, using exactly the same technique, was conducted upon individuals with aphasia. Although both subject groups benefited behaviourally from facilitation with a semantic task, different patterns of neural activation were evident. Modulation of activity was identified within regions associated with lexical-semantic processing, over the long-term for controls and over both the long- and the short-term for participants with aphasia. However, short-term facilitatory effects for control participants were found in regions linked to episodic memory and object recognition mechanisms. The phonological studies explored the effects of naming facilitation from a phonologically-based auditory repetition task administered in the presence of a picture. An experiment using this technique was conducted with healthy controls and a separate experiment with individuals with aphasia. Greater positive behavioural effects were shown in this phonological study than in the semantic study, for both controls and participants with aphasia. Additionally, the neuroimaging results suggested that the facilitatory effects arising from a phonological task were less selective, engaging regions associated with phonological and semantic processing in both controls and individuals with aphasia. For both subject groups these effects were evident over the long- and the short-term, with the short-term effects for control participants contributed to by modulation of activity in an area known to be involved in phonological processing. In summary, both techniques were effective in facilitating subsequent picture naming in controls and participants with aphasia to varying degrees. Taken together, the facilitation effects of a semantic verification task appeared to be somewhat selective in engaging regions associated with more efficient lexical-semantic processing during subsequent naming. On the other hand, an auditory repetition task was slightly more effective and less selective, engaging regions linked to both semantic and phonological processing, consistent with a strengthening of the connections between the two levels of processing. Although no distinct patterns emerged across individuals with aphasia regarding broader mechanisms of recovery, the results did provide evidence that right hemisphere mechanisms may be supportive of naming facilitation rather than maladaptive, and highlighted the involvement of regions not traditionally associated with language processing, particularly the cerebellum. Together, these experiments suggest that distinct neurocognitive mechanisms underlie the facilitation of naming by semantic and phonological tasks in both subject groups. An advance in our understanding of these mechanisms will inform the therapeutic facilitation of naming in the recovery of word production abilities following neurological injury. Therefore, these findings may aid the development of theoretically driven treatment selection methods and ultimately result in the provision of more targeted therapy for individuals with aphasia

Neural Substrates of Naming Following Semantic Verification in Aphasia

Semantic verification tasks can facilitate naming in healthy and aphasic individuals, however, the neurocognitive mechanisms involved are unclear, This study examined the neural mechanisms underpinning short and long-term semantic facilitation of naming in two individuals with anomia

Tracking the arcuate fasciculus in patients with aphasia

The arcuate fasciculus (AF), a white matter tract linking temporal and inferior frontal language cortices, can be disrupted in stroke patients suffering from aphasia. Using diffusion tensor imaging (DTI) tractography it is possible to track AF connections to neural regions associated with either phonological or semantic linguistic processing. The aim of the current study is to investigate the relationship between integrity of white matter microstructure and specific linguistic deficits

The neural correlates of picture naming facilitated by auditory repetition

Abstract Background Overt repetition of auditorily presented words can facilitate picture naming performance in both unimpaired speakers and individuals with word retrieval difficulties, but the underlying neurocognitive mechanisms and longevity of such effects remain unclear. This study used functional magnetic resonance imaging to examine whether different neurological mechanisms underlie short-term (within minutes) and long-term (within days) facilitation effects from an auditory repetition task in healthy older adults. Results The behavioral results showed that both short- and long-term facilitated items were named significantly faster than unfacilitated items, with short-term items significantly faster than long-term items. Neuroimaging analyses identified a repetition suppression effect for long-term facilitated items, relative to short-term facilitated and unfacilitated items, in regions known to be associated with both semantic and phonological processing. A repetition suppression effect was also observed for short-term facilitated items when compared to unfacilitated items in a region of the inferior temporal lobe linked to semantic processing and object recognition, and a repetition enhancement effect when compared to long-term facilitated items in a posterior superior temporal region associated with phonological processing. Conclusions These findings suggest that different neurocognitive mechanisms underlie short- and long-term facilitation of picture naming by an auditory repetition task, reflecting both phonological and semantic processing. More specifically, the brain areas engaged were consistent with the view that long-term facilitation may be driven by a strengthening of semantic-phonological connections. Short-term facilitation, however, appears to result in more efficient semantic processing and/or object recognition, possibly in conjunction with active recognition of the phonological form.</p

Neuroimaging the short- and long-term effects of repeated picture naming in healthy older adults

Repeated attempts to name pictures can improve subsequent naming for aphasic individuals with anomia, however, the neurocognitive mechanisms responsible for such improvements are unknown. This study investigated repeated picture naming in healthy older adults over a period of minutes (short-term) after one repetition and a period of days (long-term) after multiple repetitions. Compared to unprimed pictures, both repeated conditions showed faster naming latencies with the fastest latencies evident for the short-term condition. Neuroimaging results identified repetition suppression effects across three left inferior frontal gyrus regions of interest: for both the short- and long-term conditions in the pars orbitalis, and for long-term items in the pars triangularis and pars opercularis regions. The whole brain analysis also showed a repetition suppression effect in bilateral pars triangularis regions for the long-term condition. These findings within the inferior frontal gyrus suggest that effects of repeated naming may be driven by a mapping mechanism across multiple levels of representation, possibly reflecting different levels of learning, and lend support to the idea that processing may be hierarchically organised in the left inferior frontal gyrus. The whole brain analysis also revealed repetition suppression for the long-term condition within the posterior portion of bilateral inferior temporal gyri, which may reflect attenuation of integration processes within this region following the learning of task-relevant information