10 research outputs found
Episodic memory performance and associated grey matter volume in older adults with type 2 diabetes mellitus
Type 2 Diabetes Mellitus (DM2) results in peripheral and central nervous system complications. Recent studies suggest that DM2 accelerates age-related cognitive decline and is specifically linked to Alzheimer Disease (AD). A commonly reported impairment reported in DM2 is in learning and memory, and macroscopic brain changes that could mediate memory impairments can be detected by quantifying grey matter volume with Magnetic Resonance Imaging (MRI). This thesis project predicts that older adults in DM2 have impaired learning and memory compared with older adults without DM2. Additionally, the DM2 group would have decreases in grey matter volume of the hippocampus and associated brain regions, which would mediate memory function. The study found that the DM2 group performed significantly worse on two validated neuropsychological measures of learning, recall and recognition. The difference was highly significant in the learning and memory of face-name pairs, suggesting that assessing higher-level memory functions could be a sensitive marker for subtle memory impairments. However, the two groups did not differ in grey matter volume of the hippocampus, the medial temporal lobe, or the hippocampal network. Additionally, grey matter volume was not associated with learning and memory measures. The findings suggest that memory changes in DM2 may not be mediated by brain atrophy, rather could be mediated by microscopic brain changes earlier in AD progression such as beta amyloid accumulation, hyperphosphorylated tau protein, or reduced synaptic plasticity
Cerebellar tDCS: A Novel Approach to Augment Language Treatment Post-stroke
People with post-stroke aphasia may have some degree of chronic deficit for which current rehabilitative treatments are variably effective. Accumulating evidence suggests that transcranial direct current stimulation (tDCS) may be useful for enhancing the effects of behavioral aphasia treatment. However, it remains unclear which brain regions should be stimulated to optimize effects on language recovery. Here, we report on the therapeutic potential of right cerebellar tDCS in augmenting language recovery in SMY, who sustained bilateral MCA infarct resulting in aphasia and anarthria. We investigated the effects of 15 sessions of anodal cerebellar tDCS coupled with spelling therapy using a randomized, double-blind, sham controlled within-subject crossover trial. We also investigated changes in functional connectivity using resting state functional magnetic resonance imaging before and 2 months post-treatment. Both anodal and sham treatments resulted in improved spelling to dictation for trained and untrained words immediately after and 2 months post-treatment. However, there was greater improvement with tDCS than with sham, especially for untrained words. Further, generalization to written picture naming was only noted during tDCS but not with sham. The resting state functional connectivity data indicate that improvement in spelling was accompanied by an increase in cerebro-cerebellar network connectivity. These results highlight the therapeutic potential of right cerebellar tDCS to augment spelling therapy in an individual with large bilateral chronic strokes
Preserved processing of musical syntax in a person with agrammatic aphasia
A growing body of work suggests that processing hierarchical structure in language and in music rely on shared systems (review: Slevc, 2012), however this conclusion is tempered by neuropsychological dissociations between linguistic and musical processing (i.e., aphasia and amusia; review: Peretz, 2006). An influential reconciliation comes from Patel’s (2003) shared syntactic integration resource hypothesis (SSIRH), which suggests that evidence for shared processes reflect reliance on shared syntactic integration processes whereas dissociations result from damage to domain-specific syntactic representations.
The SSIRH thus predicts that patients with deficits in the processing of linguistic syntax–such as agrammatic aphasics–should show parallel deficits in musical structural (harmonic) processing. This prediction is countered by findings of impaired harmonic processing in patients with (apparently) spared linguistic syntactic processing (e.g., Sammler et al., 2011), however evidence for the opposite dissociation–preserved harmonic processing in agrammatic aphasia–is lacking. While there are reports of preserved musical abilities despite global aphasia (Basso & Capitani, 1985) or severe Wernicke’s aphasia (Luria, Tsvetkova, & Futer, 1965), of preserved reading and writing of music in the face of alexia and agraphia (Signoret et al., 1987), and of preserved musical sound naming in the face of severe anomia (Tzortzis et al., 2000), no study (to our knowledge) has demonstrated preserved musical structural processing in an agrammatic patient. In addition, at least one group of agrammatic aphasics did not show normal effects of harmonic priming, and showed a relationship between accuracy on acceptability judgments in language and in music (Patel et al., 2008).
Here, we report a detailed analysis of structural processing in language and in music in HV, a 63 year-old native English-speaking female musician who sustained a left peri-Sylvian stroke. She showed a profile of Broca’s aphasia with agrammatic speech (WAB aphasia quotient = 33.6; Fluency = 2/10, Proportion grammatical sentences = 0.04). We evaluated HV’s linguistic and musical structural processing, as well as that of twelve age-matched control participants, using matched “off-line” acceptability judgment tasks and “on-line” priming tasks.
HV performed much worse than controls when judging sentences that sometimes contained morphosyntactic violations (Crawford’s t = -3.84, p < .01), however she performed as well as controls when judging chord sequences that sometimes contained a chord from a distant key (t = -0.47). Similarly, HV showed no sensitivity to syntactic violations in a word-monitoring task, unlike control participants (t = -4.81, p < .001), however she showed normal harmonic priming effects (t = -0.30). HV thus showed a classical dissociation between linguistic and musical syntactic processing (assessed with Crawford & Garthwaite’s (2005) Revised Standardized Difference Test) for both off-line (t = 2.52, p < .05) and on-line (t = 2.65, p < .05) measures.
To our knowledge, this is the first non-anecdotal report of a patient with agrammatic aphasia demonstrating preserved harmonic processing abilities, posing a challenge for claims of a straightforward link between syntactic processing in language and music
Right Hemisphere Regions Critical for Expression of Emotion Through Prosody
Impaired expression of emotion through pitch, loudness, rate, and rhythm of speech (affective prosody) is common and disabling after right hemisphere (RH) stroke. These deficits impede all social interactions. Previous studies have identified cortical areas associated with impairments of expression, recognition, or repetition of affective prosody, but have not identified critical white matter tracts. We hypothesized that: (1) differences across patients in specific acoustic features correlate with listener judgment of affective prosody and (2) these differences are associated with infarcts of specific RH gray and white matter regions. To test these hypotheses, 41 acute ischemic RH stroke patients had MRI diffusion weighted imaging and described a picture. Affective prosody of picture descriptions was rated by 21 healthy volunteers. We identified percent damage (lesion load) to each of seven regions of interest previously associated with expression of affective prosody and two control areas that have been associated with recognition but not expression of prosody. We identified acoustic features that correlated with listener ratings of prosody (hereafter “prosody acoustic measures”) with Spearman correlations and linear regression. We then identified demographic variables and brain regions where lesion load independently predicted the lowest quartile of each of the “prosody acoustic measures” using logistic regression. We found that listener ratings of prosody positively correlated with four acoustic measures. Furthermore, the lowest quartile of each of these four “prosody acoustic measures” was predicted by sex, age, lesion volume, and percent damage to the seven regions of interest. Lesion load in pars opercularis, supramarginal gyrus, or associated white matter tracts (and not control regions) predicted lowest quartile of the four “prosody acoustic measures” in logistic regression. Results indicate that listener perception of reduced affective prosody after RH stroke is due to reduction in specific acoustic features caused by infarct in right pars opercularis or supramarginal gyrus, or associated white matter tracts
Optimal number of pulses as outcome measures of neuronavigated transcranial magnetic stimulation
•The minimum number of pulses for reliable amplitude and latency of motor evoked potentials was 21 and 23 in response to neuronavigated single-pulse TMS, respectively.•The minimum number of pulses for reliable short-interval intracortical inhibition and intracortical facilitation was 20 and 25, respectively.•Navigated transcranial magnetic stimulation might reduce the number of pulses necessary for reliable measurements.
Identify the optimal number of pulses necessary to achieve reliable measures of motor evoked potentials (MEPs) in transcranial magnetic stimulation (TMS) studies.
Retrospective data was obtained from 54 healthy volunteers (30 men, mean age 61.7±13.1years) who as part of prior studies had completed three blocks of 30 consecutive TMS stimuli using neuronavigation. Data from four protocols were assessed: single-pulse TMS for measures of amplitude and latency of MEPs; paired-pulse TMS for short-interval intracortical inhibition (sICI) and intracortical facilitation (ICF); and single-pulse TMS to assess the effects of intermittent theta burst stimulation (iTBS). Two statistical methods were used: an internal consistency analysis and probability of inclusion in the 95% confidence interval (CI) around the mean MEPs amplitude.
For single-pulse TMS, the minimum number of pulses needed to achieve reliable amplitude and latency MEPs measures was 21 and 23, respectively. For paired-pulse TMS, the minimum number of pulses needed to achieve reliable sICI and ICF measures was 20 and 25, respectively. Finally, the minimum number of pulses needed to achieve reliable amplitude and latency MEPs measures after iTBS was 22 and 23, respectively.
This study provides guidelines regarding the minimum number of pulses needed to achieve reliable MEPs measurements in various study protocols using neuronavigated TMS.
Results from this study have the potential to increase the reliability and quality of future neuronavigated TMS studies
Humans with Type-2 Diabetes Show Abnormal Long-Term Potentiation-Like Cortical Plasticity Associated with Verbal Learning Deficits
BACKGROUND: Type-2 diabetes mellitus (T2DM) accelerates cognitive aging and increases risk of Alzheimer’s disease. Rodent models of T2DM show altered synaptic plasticity associated with reduced learning and memory. Humans with T2DM also show cognitive deficits, including reduced learning and memory, but the relationship of these impairments to the efficacy of neuroplastic mechanisms has never been assessed. OBJECTIVE: Our primary objective was to compare mechanisms of cortical plasticity in humans with and without T2DM. Our secondary objective was to relate plasticity measures to standard measures of cognition. METHODS: A prospective cross-sectional cohort study was conducted on 21 adults with T2DM and 15 demographically-similar non-diabetic controls. Long-term potentiation-like plasticity was assessed in primary motor cortex by comparing the amplitude of motor evoked potentials (MEPs) from single-pulse transcranial magnetic stimulation before and after intermittent theta-burst stimulation (iTBS). Plasticity measures were compared between groups and related to neuropsychological scores. RESULTS: In T2DM, iTBS-induced modulation of MEPs was significantly less than controls, even after controlling for potential confounds. Furthermore, in T2DM, modulation of MEPs 10-min post-iTBS was significantly correlated with Rey Auditory Verbal Learning Task (RAVLT) performance. CONCLUSION: Humans with T2DM show abnormal cortico-motor plasticity that is correlated with reduced verbal learning. Since iTBS after-effects and the RAVLT are both NMDA receptor-dependent measures, their relationship in T2DM may reflect brain-wide alterations in the efficacy of NMDA receptors. These findings offer novel mechanistic insights into the brain consequences of T2DM and provide a reliable means to monitor brain health and evaluate the efficacy of clinical interventions