Treatment effects on event-related EEG potentials and oscillations in Alzheimer's disease

Comparing levetiracetam and zonisamide effects on rivastigmine anti-Alzheimer's activity in aluminum chloride-induced Alzheimer's-like disease in rats: Impact on α7 nicotinic acetylcholine receptors and amyloid β

BACKGROUND AND AIM

Alzheimer's disease (AD) is the most progressive form of neurodegenerative disease, which severely impairs cognitive function. The leading class of drugs used to treat AD is acetylcholinesterase inhibitors (AChE-Is) as Rivastigmine (RIVA), partially ameliorate its cognitive symptoms. Since epilepsy is a common comorbidity with AD, we explored the potential that new the antiepileptic drugs; Levetiracetam (LEV) and Zonisamide (ZNS) may possess an additional therapeutic benefit to RIVA in AlCl3-induced AD rat model.

MATERIALS AND METHODS

AlCl3 was used to provoke AD in rats which were then supplemented with treatment drugs for 2 weeks. Treated groups were: Control, AlCl3, RIVA, LEV, RIVA + LEV, ZNS and RIVA + ZNS. Then, the behavioral tests; passive avoidance (PA), Morris water maze (MWM) and novel object recognition (NOR) were conducted to assess cognitive behavior and memory. The Hippocampal Aβ assembly was thoroughly examined by histopathology and ELISA. α7 Nicotinic ACh receptors' (α7nAChRs) expression was assessed immunohistochemically and by real-time quantitative polymerase chain reaction (qPCR). Caspase 3 expression was also assessed by real-time qPCR in hippocampal tissues.

RESULTS

AlCl3 administration impaired memory and cognitive functions in rats, augmented hippocampal Aβ deposition, with subsequent neurodegeneration and α7nAChRs down-regulation. LEV, but not ZNS, administration significantly mitigated AlCl3-induced cognitive impairment probably through suppression of amyloid β (Aβ) deposition, enhancement of neurogenesis and α7nAChRs expression. When combined to RIVA, ZNS treatment negatively affected cognition possibly through its impact on hippocampal Aβ and subsequent neuronal damage.

CONCLUSION

Although our results indicated that neither LEV nor ZNS provided any extra benefit to cognitive enhancements in AD rats receiving rivastigmine, LEV demonstrated positive effects individually while ZNS had negative effects when combined with RIVA. As a result, this study suggests the use of LEV rather than ZNS for managing epilepsy in patients with AD given that Alzheimer's and epilepsy can coexist.

Electrophysiological correlates of visual short-term memory binding deficits in community-dwelling seniors at risk of dementia

BACKGROUND

Visual Short-Term Memory Binding (VSTMB) is a preclinical marker of Alzheimer's disease (AD). Reduced early event-related potentials (ERPs) (100-250 ms) over fronto-central (FC) and parieto-occipital (PO) regions have been reported in patients with Mild Cognitive Impairment (MCI) seen in the clinic. We investigated such ERPs in a larger sample of community-dwelling older adults who had not sought medical advice.

METHODS

Participants (n = 215) were assessed with a neuropsychological battery and the VSTMB Task. The latter assessed the ability to detect changes between two consecutive arrays of shapes or colored shapes (the Binding condition). Time-locked EEG signals were collected during the task.

RESULTS

Those who met the MCI criteria (n = 108) showed binding impairment. ERP analyses revealed significant Group x Time Windows interactions. Early ERP showed reduced neural recruitment (MCI < healthy controls (HC)) over the right FC regions, left PO, and right centro-parietal (CP) regions during Binding encoding, and over PO regions bilaterally and left FC during retrieval. Late ERP showed increased neural recruitment (MCI > HC) on left FC and PO regions during retrieval.

CONCLUSIONS

Hyper-recruitment may reflect functional reorganization aimed at behavioral compensation in the early stages of MCI. The role of such amplitude shifts as pointers of transition points in the AD continuum needs further investigation.

Auditory brainstem responses as a biomarker for cognition

A non-invasive, accessible and effective biomarker is critical to the diagnosis, monitoring and treatment of age-related cognitive decline. Recent work has suggested a strong association between auditory brainstem responses (ABR) and cognitive function in aging macaques. Here we show in 118 human participants (66 females; age range=18-92 years; hearing loss = -5 to 70 dB HL) that cognition is associated with both age and hearing level, but this triad relationship is mainly driven by the age factor. After adjusting for age, cognition is still significantly associated with both the ABR wave V amplitude (B, 0.110, 95% CI, 0.018- 0.202; p = 0.020) and latency (B, -0.101, 95% CI, -0.186- -0.016; p = 0.021). Importantly, this age-adjusted ABR-cognition association is primarily driven by older individuals and language-dependent cognitive functions. We also perform the area under the curve (AUC) of the receiver-operating-characteristic analysis and find that the ABR wave V amplitude is best for detecting good cognitive performers (AUC = 0.96) whereas the wave V latency is best for detecting poor ones (AUC = 0.86). The present result not only confirms the previous animal work in humans but also shows the clinical potential of using auditory brainstem responses to improve diagnosis and treatment of age-related cognitive decline.

Parallel electrophysiological abnormalities due to COVID-19 infection and to Alzheimer's disease and related dementia

Many coronavirus disease 2019 (COVID-19) positive individuals exhibit abnormal electroencephalographic (EEG) activity reflecting "brain fog" and mild cognitive impairments even months after the acute phase of infection. Resting-state EEG abnormalities include EEG slowing (reduced alpha rhythm; increased slow waves) and epileptiform activity. An expert panel conducted a systematic review to present compelling evidence that cognitive deficits due to COVID-19 and to Alzheimer's disease and related dementia (ADRD) are driven by overlapping pathologies and neurophysiological abnormalities. EEG abnormalities seen in COVID-19 patients resemble those observed in early stages of neurodegenerative diseases, particularly ADRD. It is proposed that similar EEG abnormalities in Long COVID and ADRD are due to parallel neuroinflammation, astrocyte reactivity, hypoxia, and neurovascular injury. These neurophysiological abnormalities underpinning cognitive decline in COVID-19 can be detected by routine EEG exams. Future research will explore the value of EEG monitoring of COVID-19 patients for predicting long-term outcomes and monitoring efficacy of therapeutic interventions. HIGHLIGHTS: Abnormal intrinsic electrophysiological brain activity, such as slowing of EEG, reduced alpha wave, and epileptiform are characteristic findings in COVID-19 patients. EEG abnormalities have the potential as neural biomarkers to identify neurological complications at the early stage of the disease, to assist clinical assessment, and to assess cognitive decline risk in Long COVID patients. Similar slowing of intrinsic brain activity to that of COVID-19 patients is typically seen in patients with mild cognitive impairments, ADRD. Evidence presented supports the idea that cognitive deficits in Long COVID and ADRD are driven by overlapping neurophysiological abnormalities resulting, at least in part, from neuroinflammatory mechanisms and astrocyte reactivity. Identifying common biological mechanisms in Long COVID-19 and ADRD can highlight critical pathologies underlying brain disorders and cognitive decline. It elucidates research questions regarding cognitive EEG and mild cognitive impairment in Long COVID that have not yet been adequately investigated.

Age-Related Aspects of Sex Differences in Event-Related Brain Oscillatory Responses: A Turkish Study

Earlier research has suggested gender differences in event-related potentials/oscillations (ERPs/EROs). Yet, the alteration in event-related oscillations (EROs) in the delta and theta frequency bands have not been explored between genders across the three age groups of adulthood, i.e., 18-50, 51-65, and >65 years. Data from 155 healthy elderly participants who underwent a neurological examination, comprehensive neuropsychological assessment (including attention, memory, executive function, language, and visuospatial skills), and magnetic resonance imaging (MRI) from past studies were used. The delta and theta ERO powers across the age groups and between genders were compared and correlational analyses among the ERO power, age, and neuropsychological tests were performed. The results indicated that females displayed higher theta ERO responses than males in the frontal, central, and parietal regions but not in the occipital location between 18 and 50 years of adulthood. The declining theta power of EROs in women reached that of men after the age of 50 while the theta ERO power was more stable across the age groups in men. Our results imply that the cohorts must be recruited at specified age ranges across genders, and clinical trials using neurophysiological biomarkers as an intervention endpoint should take gender into account in the future.

Transcranial alternating current stimulation in affecting cognitive impairment in psychiatric disorders: a review

Transcranial alternating current stimulation (tACS) is a non-invasive brain stimulation method that, through its manipulation of endogenous oscillations, can affect cognition in healthy adults. Given the fact that both endogenous oscillations and cognition are impaired in various psychiatric diagnoses, tACS might represent a suitable intervention. We conducted a search of Pubmed and Web of Science databases and reviewed 27 studies where tACS is used in psychiatric diagnoses and cognition change is evaluated. TACS is a safe and well-tolerated intervention method, suitable for multiple-sessions protocols. It can be administered at home, individualized according to the patient''s anatomical and functional characteristics, or used as a marker of disease progression. The results are varying across diagnoses and applied protocols, with some protocols showing a long-term effect. However, the overall number of studies is small with a great variety of diagnoses and tACS parameters, such as electrode montage or used frequency. Precise mechanisms of tACS interaction with pathophysiological processes are only partially described and need further research. Currently, tACS seems to be a feasible method to alleviate cognitive impairment in psychiatric patients; however, a more robust confirmation of efficacy of potential protocols is needed to introduce it into clinical practise.

A distributed theta network of error generation and processing in aging

Based on previous concepts that a distributed theta network with a central "hub" in the medial frontal cortex is critically involved in movement regulation, monitoring, and control, the present study explored the involvement of this network in error processing with advancing age in humans. For that aim, the oscillatory neurodynamics of motor theta oscillations was analyzed at multiple cortical regions during correct and error responses in a sample of older adults. Response-related potentials (RRPs) of correct and incorrect reactions were recorded in a four-choice reaction task. RRPs were decomposed in the time-frequency domain to extract oscillatory theta activity. Motor theta oscillations at extended motor regions were analyzed with respect to power, temporal synchronization, and functional connectivity. Major results demonstrated that errors had pronounced effects on motor theta oscillations at cortical regions beyond the medial frontal cortex by being associated with (1) theta power increase in the hemisphere contra-lateral to the movement, (2) suppressed spatial and temporal synchronization at pre-motor areas contra-lateral to the responding hand, (2) inhibited connections between the medial frontal cortex and sensorimotor areas, and (3) suppressed connectivity and temporal phase-synchronization of motor theta networks in the posterior left hemisphere, irrespective of the hand, left, or right, with which the error was made. The distributed effects of errors on motor theta oscillations demonstrate that theta networks support performance monitoring. The reorganization of these networks with aging implies that in older individuals, performance monitoring is associated with a disengagement of the medial frontal region and difficulties in controlling the focus of motor attention and response selection.

Supplementary Information

The online version contains supplementary material available at 10.1007/s11571-023-10018-4.

Aging alters functional connectivity of motor theta networks during sensorimotor reactions

OBJECTIVE

Both cognitive and primary motor networks alter with advancing age in humans. The networks activated in response to external environmental stimuli supported by theta oscillations remain less well explored. The present study aimed to characterize the effects of aging on the functional connectivity of response-related theta networks during sensorimotor tasks.

METHODS

Electroencephalographic signals were recorded in young and middle-to-older age adults during three tasks performed in two modalities, auditory and visual: a simple reaction task, a Go-NoGo task, and a choice-reaction task. Response-related theta oscillations were computed. The phase-locking value (PLV) was used to analyze the spatial synchronization of primary motor and motor control theta networks.

RESULTS

Performance was overall preserved in older adults. Independently of the task, aging was associated with reorganized connectivity of the contra-lateral primary motor cortex. In younger adults, it was synchronized with motor control regions (intra-hemispheric premotor/frontal and medial frontal). In older adults, it was only synchronized with intra-hemispheric sensorimotor regions.

CONCLUSIONS

Motor theta networks of older adults manifest a functional decoupling between the response-generating motor cortex and motor control regions, which was not modulated by task variables. The overall preserved performance in older adults suggests that the increased connectivity within the sensorimotor network is associated with an excessive reliance on sensorimotor feedback during movement execution compensating for a deficient cognitive regulation of motor regions during sensorimotor reactions.

SIGNIFICANCE

New evidence is provided for the reorganization of motor networks during sensorimotor reactions already at the transition from middle to old age.

State-of-the-art imaging of neuromodulatory subcortical systems in aging and Alzheimer's disease: Challenges and opportunities

Primary prevention trials have shifted their focus to the earliest stages of Alzheimer's disease (AD). Autopsy data indicates that the neuromodulatory subcortical systems' (NSS) nuclei are specifically vulnerable to initial tau pathology, indicating that these nuclei hold great promise for early detection of AD in the context of the aging brain. The increasing availability of new imaging methods, ultra-high field scanners, new radioligands, and routine deep brain stimulation implants has led to a growing number of NSS neuroimaging studies on aging and neurodegeneration. Here, we review findings of current state-of-the-art imaging studies assessing the structure, function, and molecular changes of these nuclei during aging and AD. Furthermore, we identify the challenges associated with these imaging methods, important pathophysiologic gaps to fill for the AD NSS neuroimaging field, and provide future directions to improve our assessment, understanding, and clinical use of in vivo imaging of the NSS.