Investigating silent pauses in connected speech: integrating linguistic, neuropsychological, and neuroanatomical perspectives across narrative tasks in post-stroke aphasia

Introduction

Silent pauses are regarded as integral components of the temporal organization of speech. However, it has also been hypothesized that they serve as markers for internal cognitive processes, including word access, monitoring, planning, and memory functions. Although existing evidence across various pathological populations underscores the importance of investigating silent pauses' characteristics, particularly in terms of frequency and duration, there is a scarcity of data within the domain of post-stroke aphasia.

Methods

The primary objective of the present study is to scrutinize the frequency and duration of silent pauses in two distinct narrative tasks within a cohort of 32 patients with chronic post-stroke aphasia, in comparison with a control group of healthy speakers. Subsequently, we investigate potential correlation patterns between silent pause measures, i.e., frequency and duration, across the two narrative tasks within the patient group, their performance in neuropsychological assessments, and lesion data.

Results

Our findings showed that patients exhibited a higher frequency of longer-duration pauses in both narrative tasks compared to healthy speakers. Furthermore, within-group comparisons revealed that patients tended to pause more frequently and for longer durations in the picture description task, while healthy participants exhibited the opposite trend. With regard to our second research question, a marginally significant interaction emerged between performance in semantic verbal fluency and the narrative task, in relation to the location of silent pauses-whether between or within clauses-predicting the duration of silent pauses in the patient group. However, no significant results were observed for the frequency of silent pauses. Lastly, our study identified that the duration of silent pauses could be predicted by distinct Regions of Interest (ROIs) in spared tissue within the left hemisphere, as a function of the narrative task.

Discussion

Overall, this study follows an integrative approach of linguistic, neuropsychological and neuroanatomical data to define silent pauses in connected speech, and illustrates interrelations between cognitive components, temporal aspects of speech, and anatomical indices, while it further highlights the importance of studying connected speech indices using different narrative tasks.

Clinical feasibility of diffusion microstructure imaging (DMI) in acute ischemic stroke

BACKGROUND

Diffusion microstructure imaging (DMI) is a fast approach to higher-order diffusion-weighted magnetic resonance imaging that allows robust decomposition and characterization of diffusion properties of brain tissue into intra-axonal, extra-axonal, and a free water-compartment. We now report the application of this technique to acute ischemic stroke and demonstrate its potential applicability to the daily clinical routine.

METHODS

Thirty-eight patients diagnosed with acute ischemic stroke were scanned using an accelerated multi-shell diffusion-weighted imaging protocol (median delay between onset and MRI scan of 113 min). DMI metrics were calculated and the apparent diffusion coefficient (ADC) derived from conventional diffusion-weighted imaging was used for comparison. The resulting DMI parameter maps were analysed for their potential to improve infarct core delineation, and a receiver-operating characteristic (ROC) analysis was subsequently performed for automated infarct segmentation.

RESULTS

Robust parameter maps for diffusion microstructure properties were obtained in all cases. Within the ischemic tissue, an increase in the volume fraction of the intra-axonal compartment was accompanied by a volume fraction reduction in the other two compartments. Moreover, diffusivity was reduced in all three compartments, with intra-axonal diffusivity showing the highest degree of contrast. The intra-axonal diffusion coefficient maps were subsequently found to perform better than single-shell ADC-derived segmentation in terms of automatic segmentation of the infarct core (area under the curve = 0.98 vs 0.92).

CONCLUSIONS

The alterations to the ischemic core detected by DMI are in line with the "beading-model" of non-uniform neurite swelling under ischemic conditions. When compared to conventional single-shell diffusion-weighted imaging, DMI metrics are associated with improved discriminative power for delineating and characterizing ischemic changes. This might allow a more detailed assessment of infarct age, severity of damage, the degree of reversibility, and outcome.

Displaying the autonomic processing network in humans - a global tractography approach

Regulation of the internal homeostasis is modulated by the central autonomic system. So far, the view of this system is determined by animal and human research focusing on cortical and subcortical grey substance regions. To provide an overview based on white matter architecture, we used a global tractography approach to reconstruct a network of tracts interconnecting brain regions that are known to be involved in autonomic processing. Diffusion weighted imaging data were obtained from subjects of the human connectome project (HCP) database. Resulting tracts are in good agreement with previous studies assuming a division of the central autonomic system into a cortical (CAN) and a subcortical network (SAN): the CAN consist of three subsystems that encompass all cerebral lobes and overlap within the insular cortex: a parieto-anterior-temporal pathway (PATP), an occipito-posterior-temporo-frontal pathway (OPTFP) and a limbic pathway. The SAN on the other hand connects the hypothalamus to the periaqueductal grey and locus coeruleus, before it branches into a dorsal and a lateral part that target autonomic nuclei in the rostral medulla oblongata. Our approach furthermore reveals how the CAN and SAN are interconnected: the hypothalamus can be considered as the interface-structure of the SAN, whereas the insula is the central hub of the CAN. The hypothalamus receives input from prefrontal cortical fields but is also connected to the ventral apex of the insular cortex. Thus, a holistic view of the central autonomic system could be created that may promote the understanding of autonomic signaling under physiological and pathophysiological conditions.

Ventral tegmental area connections to motor and sensory cortical fields in humans

In humans, sensorimotor cortical areas receive relevant dopaminergic innervation—although an anatomic description of the underlying fiber projections is lacking so far. In general, dopaminergic projections towards the cortex originate within the ventral tegmental area (VTA) and are organized in a meso-cortico-limbic system. Using a DTI-based global tractography approach, we recently characterized the superolateral branch of the medial forebrain bundle (slMFB), a prominent pathway providing dopaminergic (and other transmitters) innervation for the pre-frontal cortex (Coenen et al., NeuroImage Clin 18:770–783, 2018). To define the connections between VTA and sensory–motor cortical fields that should contain dopaminergic fibers, we use the slMFB as a key structure to lead our fiber selection procedure: using a similar tracking-seed and tractography algorithm, we describe a dorsal extension of this slMFB that covers sensorimotor fields that are dorsally appended to pre-frontal cortical areas. This “motorMFB”, that connects the VTA to sensorimotor cortical fields, can be further segregated into three sub-bundles with a seed-based fiber-selection strategy: A PFC bundle that is attendant to the pre-frontal cortex, passes the lateral VTA, runs through the border zone between the posterior and lateral ventral thalamic nucleus, and involves the pre- and postcentral gyrus. An MB bundle that is attendant to the mammillary bodies runs directly through the medial VTA, passes the lateral ventral thalamic nucleus, and involves the pre- and postcentral gyrus as well as the supplementary motor area (SMA) and the dorsal premotor cortex (dPMC). Finally, a BC bundle that is attendant to the brainstem and cerebellum runs through the lateral VTA, passes the anterior ventral thalamic nucleus, and covers the SMA, pre-SMA, and the dPMC. We, furthermore, included a fiber tracking of the well-defined dentato-rubro-thalamic tract (DRT) that is known to lie in close proximity with respect to fiber orientation and projection areas. As expected, the tract is characterized by a decussation at the ponto-mesencephal level and a projection covering the superior-frontal and precentral cortex. In addition to the physiological role of these particular bundles, the physiological and pathophysiological impact of dopaminergic signaling within sensorimotor cortical fields becomes discussed. However, some limitations have to be taken into account in consequence of the method: the transmitter content, the directionality, and the occurrence of interposed synaptic contacts cannot be specified.

Post-stroke insomnia in community-dwelling patients with chronic motor stroke: Physiological evidence and implications for stroke care

Questionnaire studies suggest that stroke patients experience sustained problems with sleep and daytime sleepiness, but physiological sleep studies focussing specifically on the chronic phase of stroke are lacking. Here we report for the first time physiological data of sleep and daytime sleepiness obtained through the two gold-standard methods, nocturnal polysomnography and the Multiple Sleep Latency Test. Data from community-dwelling patients with chronic right-hemispheric stroke (>12 months) were compared to sex- and age-matched controls. Behavioural and physiological measures suggested that stroke patients had poorer sleep with longer sleep latencies and lower sleep efficiency. Patients further spent more time awake during the night, and showed greater high-frequency power during nonREM sleep than controls. At the same time the Multiple Sleep Latency Test revealed greater wake efficiency in patients than controls. Importantly these findings were not due to group differences in sleep disordered breathing or periodic limb movements. Post-stroke insomnia is presently not adequately addressed within the care pathway for stroke. A holistic approach to rehabilitation and care provision, that includes targeted sleep interventions, is likely to enhance long-term outcome and quality of live in those living with chronic deficits after stroke.

Vergleich von MRT- und SPECT-Befunden bei Patienten mit zerebraler Mikroangiopathie

Lacunar infarctions and periventricular hypodensity are assumed to be typical CT patterns of cerebral microangiopathy (MA). In 17 patients with such findings and in 6 controls without any signs of central nervous system disease cranial CT, MRT and 99mTc-HMPAO-SPECT were employed. In 7 patients with CT findings of minor MA demonstrated in comparison to controls no significant difference. In 10 cases with CT findings of pronounced MA periventricular rCBF was significantly reduced compared to controls. rCBF of temporal and parietal cortex were not diminished compared to controls. In 14 patients studied with MRT deep white matter lesions were found which appeared solitary, multiple or confluent. Employing 99mTc-HMPAO-SPECT, cerebral MA revealed rCBF reduction in periventricular brain tissue by cerebellar standardization.

Combined SPECT Imaging of Regional Cerebral Blood Flow (99mTc-HexamethylPropyleneamine Oxime, HMPAO) and Blood Volume (99mTc-RBC) to Assess Regional Cerebral Perfusion Reserve in Patients with Cerebrovascular Disease

In 53 patients with cerebrovascular disease (CVD), regional cerebral blood flow (CBF) and blood volume (CBV) were imaged by SPECT within one session. Slice division (CBF: CBV) yielded distribution of regional cerebral perfusion reserve (CPR). Semiquantitative evaluation was obtained from manually set ROIs by interhemispherical ratios (for CBF, CBV and CPR), using 2 SD from a normal group (n = 10) as a threshold. Sensitivities were 59% for CBF, 94% for CBV and 83% for CPR. Combined sensitivity was 98%. Establishing three constellations for CBF, CBV and CPR, regionally normal CBFs but quantitatively increased CBVs (+69%) and decreased CPRs (−31 %) were found in relatively early stages of CVD. Very advanced cases showed decreased CBFs (−65%), CBVs (−40%), CPRs (−49%) and a surrounding penumbra. In 87% (46/53 patients), such Theologically postulated constellations could be demonstrated. We conclude that combined CBF and CBV SPECT, assisted by CPR images, is a promising tool to detect CVD and to assess its individual regional severity.

Rolle der Positronen-Emissions-Tomographie (PET) und Single-Photon-Emissions-Tomographie (SPECT) bei der sogenannten »Multiple Chemical Sensitivity« (MCS)

Die funktionell bildgebenden Verfahren SPECT und PET werden zunehmend genutzt, um die Existenz eines Syndroms der erworbenen Chemikalienüberempfindlichkeit »Multiple Chemical Sensitivity« (MCS) nachzuweisen. In der Folge spielen SPECT und PET-Befunde auch im Rahmen von Gutachten bei Berufskrankheiten-Anzeigen als Beweismittel eine große Rolle. In der vorliegenden Arbeit wird die zu diesem Thema existierende Literatur einer kritischen Betrachtung unterzogen. Die Autoren kommen zu dem Schluß, daß die gegenwärtig verfügbaren Daten nicht ausreichen, um die Existenz eines solchen Syndroms nachzuweisen. Die niedrige Spezifität der beschriebenen Veränderungen macht es sehr schwierig, einen kausalen Zusammenhang zu der toxischen Exposition herzustellen, und schränkt den Wert von PET und vor allem SPECT bei gutachterlichen Fragestellungen in diesem Zusammenhang ein.

Clinical applications of single photon emission tomography in neuromedicine

This article gives in his second part a critical review of the clinical applications of SPECT with perfusion markers and receptor ligands in dementing disorders and psychosis. In addition this review discusses clinical applications of SPECT investigations with perfusion markers in inflammatory diseases of the central nervous system and in brain trauma.

Clinical applications of single photon emission tomography in neuromedicine

Single photon emission tomography is, because of its availability and the relatively low costs, the functional imaging modality currently most widely used for clinical applications in the brain. Beside the application of radiopharmaceuticals for the assessment of regional cerebral blood flow there is an increasing clinical use of more selective SPECT-radiopharmaceuticals, like amino acid analogs or receptor ligands. This article gives in his first part a critical review of the clinical applications of SPECT in neuro-oncology, epilepsy, basal ganglia disorders and cerebrovascular disease.

Motor cortex excitability and fatigue in multiple sclerosis: a transcranial magnetic stimulation study

We investigated electrophysiological correlates of fatigue in patients with multiple sclerosis (MS). Transcranial magnetic stimulation (TMS) was used to explore motor excitability in three groups of subjects: MS patients with fatigue (MS-F), MS patients without fatigue (MS-NF) and healthy control subjects. All participants had to perform a fatiguing hand-grip exercise. TMS was performed prior to and after the exercise. Prior to the motor task, MS-F patients had less inhibition in the primary motor cortex compared to both other groups. Postexercise, intracortical inhibition was still reduced in the MS-F patients compared to the MS-NF patients. In MS-F patients the postexercise time interval for normalization of the motor threshold was correlated with the fatigue severity. We conclude that MS patients with fatigue have an impairment of inhibitory circuits in their primary motor cortex. The results also indicate that fatigue severity is associated with an exercise-induced reduction of membrane excitability.

Transcranial sonography and [18F]fluorodeoxyglucose positron emission tomography for the differential diagnosis of parkinsonism: a head-to-head comparison

BACKGROUND AND PURPOSE

Brain imaging with positron emission tomography using [(18) F]fluorodeoxyglucose (FDG-PET) and transcranial B-mode sonography (TCS) improves the differential diagnosis of parkinsonism. The diagnostic merits of these approaches in identifying and differentiating atypical parkinsonian syndromes (APS) are compared.

METHODS

Data were included from 36 patients with clinically suspected APS who underwent PET and TCS. FDG-PET scans were analyzed by visual assessment (including voxel-based statistical maps) of a priori defined disease-specific metabolic patterns. Sonographers achieved diagnoses according to pre-defined criteria for echogenicities of the substantia nigra and lenticular nucleus, and third ventricle diameter. Patients with APS were identified and allocated to the subgroups multiple system atrophy (MSA), progressive supranuclear palsy (PSP) or corticobasal degeneration (CBD).

RESULTS

After a median follow-up period of 9 months, the final clinical diagnoses (reference standard) were Parkinson's disease, n = 15; MSA, n = 9; PSP, n = 7; and CBD, n = 5 (n = 21 APS in total). Six patients (4 APS) showed an insufficient bone window for TCS. In the remaining 30 patients, sensitivity/specificity for diagnosing APS were 82%/100% and 82%/85% for FDG-PET and TCS, respectively. Diagnostic accuracies did not differ between FDG-PET (90%) and TCS (83%; P = 0.69). Likewise, overall accuracy of subgroup classification (non-APS, MSA, PSP and CBD) did not differ between modalities (FDG-PET 87% and TCS 83%; P = 1.00).

CONCLUSIONS

FDG-PET and TCS show comparable accuracies for differential diagnosis of neurodegenerative parkinsonism. This preliminary study supports the use of TCS and warrants further prospective validation.