Background Parkinson’s disease is associated with increased impulsivity, which can be divided into several domains: motor (consisting of proactive and reactive subdomains), reflection, and cognitive ...impulsivity. Evidence suggests that both dopaminergic medication and subthalamic nucleus deep brain stimulation can affect impulsivity. Therefore, we set out to investigate the effects of dopaminergic medication and subthalamic nucleus deep brain stimulation on motor, reflection, and cognitive impulsivity in Parkinson’s disease patients. Methods Twenty Parkinson’s disease patients who underwent subthalamic nucleus deep brain stimulation were tested ON and OFF dopaminergic medication and ON and OFF subthalamic nucleus deep brain stimulation. They performed three different impulsivity tasks: the AX continuous performance task (AX-CPT) to test for motor impulsivity, the Beads task for reflection impulsivity, and the Delay discounting task for cognitive impulsivity. Results The combination of subthalamic nucleus deep brain stimulation and dopaminergic medication led to an increase in motor impulsivity ( p = 0.036), both proactive ( p = 0.045) and reactive ( p = 0.006). There was no effect of either dopaminergic medication or subthalamic nucleus deep brain stimulation on reflection and cognitive impulsivity. Conclusion The combination of dopaminergic medication and subthalamic nucleus deep brain stimulation leads to increased motor, but not cognitive or reflection, impulsivity in patients with Parkinson’s disease. Both proactive and reactive motor impulsivity were impaired by the combination of dopaminergic medication and subthalamic nucleus deep brain stimulation.
Cognitive control has been linked to both the microstructure of individual tracts and the structure of whole-brain networks, but their relative contributions in health and disease remain unclear.
To ...determine the contribution of both localized white matter tract damage and disruption of global network architecture to cognitive control, in older age and Mild Cognitive Impairment (MCI).
Twenty-five patients with MCI and 20 age, sex, and intelligence-matched healthy volunteers were investigated with 3 Tesla structural magnetic resonance imaging (MRI). Cognitive control and episodic memory were evaluated with established tests. Structural network graphs were constructed from diffusion MRI-based whole-brain tractography. Their global measures were calculated using graph theory. Regression models utilized both global network metrics and microstructure of specific connections, known to be critical for each domain, to predict cognitive scores.
Global efficiency and the mean clustering coefficient of networks were reduced in MCI. Cognitive control was associated with global network topology. Episodic memory, in contrast, correlated with individual temporal tracts only. Relationships between cognitive control and network topology were attenuated by addition of single tract measures to regression models, consistent with a partial mediation effect. The mediation effect was stronger in MCI than healthy volunteers, explaining 23-36% of the effect of cingulum microstructure on cognitive control performance. Network clustering was a significant mediator in the relationship between tract microstructure and cognitive control in both groups.
The status of critical connections and large-scale network topology are both important for maintenance of cognitive control in MCI. Mediation via large-scale networks is more important in patients with MCI than healthy volunteers. This effect is domain-specific, and true for cognitive control but not for episodic memory. Interventions to improve cognitive control will need to address both dysfunction of local circuitry and global network architecture to be maximally effective.
V zadnjih letih je t. i. omrežna perspektiva prispevala k boljšemu razumevanju delovanja možganov pri zdravih posameznikih in bolnikih z boleznimi živčevja. Razvoj neinvazivnih slikovnih metod in ...uporaba matematičnih orodij teorije grafov sta omogočila proučevanje zgradbe in delovanja možganskih omrežij. Povezave v strukturnih omrežjih lahko rekonstruiramo s pomočjo difuzijskega magnetnoresonančnega slikanja, funkcijske slikovne metode pa omogočajo proučevanje funkcijskih omrežij. Možganske sposobnosti so odvisne od topologije omrežij, ki omogočajo tako segregacijo funkcije kot tudi integrativno procesiranje informacij. Prispevek je dostopen uvod v osnove teorije grafov in nevroznanosti omrežij. Predstavi mere topologije omrežij in osnovne značilnosti možganskih omrežij pri človeku. Članek pojasni, kako bolezenski procesi prizadenejo delovanje možganov kot omrežja, in prikaže primere prenosa v klinično prakso. Izpostavimo tudi nekaj omejitev in izzivov, s katerimi se srečuje to hitro razvijajoče se področje nevroznanosti.
Abstract
Background
Memory complaints are common in elderly and have various etiologies, including functional cognitive disorder (FCD). Diagnosis of FCD is supported by clinical evidence of ...incongruity with a neurodegenerative disorder and/or evidence of internal inconsistency ‐ the ability to perform a task well at certain times, but with impaired ability at other times. The prevalence of features suggesting FCD in organic disorders is unclear. We assessed the presence of clinical features of internal inconsistency and other possible discriminators of FCD from organic causes in patients with mild cognitive impairment (MCI) and subjective cognitive impairment (SCI).
Method
Patients attending our tertiary memory clinic in a period of one year with SCI or MCI were included. Exclusion criteria were toxic or metabolic causes of cognitive decline, major psychiatric disorders, co‐morbid neurological conditions that could affect cognition, and uncertainty of diagnosis of organic disorder or FCD. Medical records were reviewed for evidence of internal inconsistency and other suggested discriminators between functional and organic etiology. Demographic, cognitive and clinical data were compared between groups.
Result
We evaluated 39 patients with FCD and 57 with organic disorders. MCI was more common in patients with organic disorders. However, most patients with FCD also had MCI. Patients with FCD were younger and performed better on cognitive assessments, but with significant overlap between groups (Table 1). While patients with FCD more commonly attended the appointment alone and reported greater concern about their symptoms than their supporters, these features were unspecific (Table 2). Patients with FCD reported symptoms that could represent normal experiences and provided detailed descriptions of memory lapses more commonly. While less sensitive, memory perfectionism and symptoms occurring only in specific situations were highly specific for FCD.
Conclusion
Differentiation between functional and organic cognitive disorders based on history and examination can be challenging. Features suggesting internal inconsistency and incongruity with neurodegeneration may also appear in organic causes of SCI and MCI. Their varying specificity and sensitivity for FCD need to be taken into account when considering the diagnosis. Improving the identification of FCD could in turn improve identification of patients with prodromal neurodegeneration.
Structure and function of brain networks Berlot, Rok; Grega Repovš
Zdravniški vestnik (Ljubljana, Slovenia : 1992),
03/2019, Letnik:
88, Številka:
3-4
Journal Article
Recenzirano
Odprti dostop
In recent years, the so-called network perspective has led to better understanding of the functioning of the brain in health and disease. The development of non-invasive imaging methods and the use ...of mathematical tools from graph theory allowed for investigating the structure and function of brain networks. Connections within structural networks can be reconstructed using diffusion magnetic resonance imaging, while functional imaging methods allow for investigating functional networks. The capabilities of the brain are based on network topology, which allows both functional segregation and integrative processing of information. This review represents an accessible introduction to the basic principles of graph theory and network neuroscience. We introduce measures of network topology and basic properties of human brain networks. We explain how neurological and psychiatric disorders affect the functioning of the brain as a network and illustrate the relevance of these findings for clinical practice. We also highlight some limitations of the network approach and future challenges to be addressed in this rapidly developing field of neuroscience.
Background
Undetected neurodegeneration is present in many patients with stroke. Clinical consequences of stroke might be partly determined by pre‐existing changes in brain structure. Cortical ...acetylcholine allows favourable adaptation to pathological changes within the limbic system. However, it remains unclear if it acts more broadly, affecting the configuration of the structural connectome. To test this, we aimed to assess the relationship between nucleus basalis of Meynert (NBM) structure and vulnerability of the connectome to simulated strategic lesions in patients with mild cognitive impairment (MCI).
Method
Twenty patients with MCI and 20 healthy elderly controls underwent 3T structural and diffusion‐weighted MRI. Whole‐brain tractograms were represented as network graphs. Lesions of individual nodes were simulated by removing a node and its connections from the graph. The impact of simulated lesions was measured as the proportional change in global efficiency of the connectome. Relationships between NBM volume, global efficiency of intact connectomes and impacts of individual simulated lesions of network nodes were assessed, controlling for demographic variables and atrophy of individual nodes.
Result
Artificial removal of the thalamus and the hippocampus from the connectome had a lower impact on global efficiency in MCI compared to controls. In MCI, NBM volume was correlated with global efficiency of intact connectomes. Higher NBM volumes were associated with reduced impact of thalamic lesions and lesions of the entorhinal and posterior cingulate cortices. These relationships were not present in other cortical or subcortical nodes or in controls.
Conclusion
Reduced vulnerability to damage of the hippocampus and thalamus in MCI suggests that connections essential for efficient network structure “shift” away from these areas. In MCI, preserved NBM is associated with efficient network topology and has a protective effect against the global impact of simulated strategic lesions. By influencing the configuration of the connectome in MCI, the cholinergic system might have a protective effect against the impact of targeted damage. Structural connectome alterations in response to early neurodegeneration represent a potential mechanism for synergy between neurodegeneration and vascular lesions in post‐stroke cognitive impairment and mixed dementia.
PDF
