Mid-frontal Delta/Theta and Cognitive Control

Up to 80% of patients with Parkinson's disease (PD) will suffer from cognitive symptoms, including impaired attention, planning, reasoning, and working memory as well as hallucinations, visuospatial dysfunction, and delusions. These impairments lead to mild cognitive impairment (PD-MCI) and dementia (PDD) in PD. Cognitive symptoms of PD are associated with enormous costs to society. There are no clear biomarkers and few effective treatments for PD-MCI/PDD. Because risk for PD increases dramatically with age, this problem will surge as the population grows older. The mechanisms contributing to PD-MCI/PDD are unknown. The investigators have found that low-frequency (1-8 Hz; or delta/theta bands) brain rhythms might be helpful in diagnosing cognitive dysfunction in PD. This delta/theta activity originates from areas of medial frontal cortex, such as the anterior cingulate, and is detectable by mid-frontal scalp EEG electrodes. We have found that mid-frontal delta/theta brain rhythms are engaged when healthy individuals detect novelty, errors, and conflict, or make decisions. These rhythms are attenuated in PD patients. The working model is that PD patients manifest diverse neuronal and network deficits that impair mid-frontal delta/theta activity, leading to failures in engaging cognitive control. These abnormalities contribute to PD-MCI and PDD.

In this proposal, we combine 'big-data' machine learning tools and new brain-stimulation paradigms to investigate the role of mid-frontal delta/theta rhythms in PD. We will test the overall hypothesis that mid-frontal delta/theta impairments are a mechanism of cognitive dysfunction in PD. We will determine if mid-frontal delta/theta activity predicts PD-MCI/PDD and if subthalamic nucleus deep-brain stimulation (DBS) at delta/theta frequencies improves cognitive control in PD patients. Because these experiments involve EEG recordings across several PD patient populations and brain stimulation, each of these aims will provide independent mechanistic insight into cognitive dysfunction in PD. PD is a complex disease, but if cortical EEG abnormalities are a consistent theme, it might inspire new diagnostic tools or new brain-stimulation therapies for cognitive dysfunction in PD. Results from this proposal could also be important for other neurodegenerative diseases such as dementia with Lewy bodies and Alzheimer's disease.

• We will perform the study on Parkinson's disease (PD) patients. PD patient takes anti-Parkinsonian medication (Levodopa) to improve motor symptoms. Medication can change their cognitive performances and neuronal activity; therefore, we will ask (on the phone) patients to withdraw medication (the night before) so that the next morning they will be off medication. For this study, it is crucial that the washout period is >12 hours. During OFF medication, PD patients will only be slow in walking and performing motor activities. There won't be worse effects since it's a motor disorder. We will stop the experiments if the subject worsens during the washout period, and we will provide him/her medications. At the same time, the subject will be examined by the expert neurologist.
• The purpose of the other experiments that are part of this study is to investigate the functions of the specific brain circuit underlying motor and cognitive tasks. Specifically, we are interested in investigating a well-known brain area that allows humans to interrupt ongoing neural representations interacts with active, ongoing motor processes (action initiation and execution) and cognitive processes within the context of simple laboratory tasks. The interaction between neural regions underlying controlling ongoing motor and cognitive processes allows the brain circuit to improve motor action and thought processes when necessary. Typically, patients with Parkinson's disease are slow to execute motor tasks and also show impairment in cognitive performance. We will combine electroencephalography (EEG) with transcranial magnetic stimulation (TMS) to study the effects of stimulation on neuronal activity.

The study will use TMS to temporarily and reversibly alter the activity of a specific node (brain area) of the wider brain network (specifically, the pre-supplementary motor, pre-motor area, and motor cortical regions), and measure the effects of this stimulation-related alteration on neural and behavioral measurements of motor and cognitive tasks. The brain stimulation methods use different protocols of TMS to evoke internally generated neural discharges through the use of focal magnetic fields.

• All subjects will perform questionnaires related to the cognitive and motor impairments.
• Afterwards, we will record EEG and respiratory data during elementary cognitive tasks such as interval timing, oddball detection, stop-signal, and Simon choice reaction-time tasks and upper- and lower limb motor tasks (flexion and extension (such as key board pressing and pedaling), gait imagery, and observation)and at resting state (during sitting (eyes open and close) and standing on soft pad) from PD patients without PD-MCI/PDD, patients with PD-MCI, patients with PDD, and demographically-matched healthy controls. We will also include patients with Alzheimer's disease (AD) and Lewy body dementia (DLB) as control subjects since they don't have dopamine deficiency. We will also include healthy young and middle age adults as comparison groups to compare neural mechanisms of cognitive control across age groups.
• For another aim, we will record EEG with 4 Hz STN DBS during above tasks (rest, cognitive, and motor tasks ) in PD patients.
• For another study, We will record EEG with TMS during simple upper and lower limb flexion-extension motor task (such as key board pressing and pedaling), cognitive tasks (as above) and resting state (as above) in different group of PD subjects. We will not include PD subjects with DBS in TMS experiments. We will recruit PD subjects on different day only for EEG-TMS experiment.
• We will also be piloting the behavioral tasks with a small group of control subjects and PD patients. This will allow us to optimize the tasks to be used in all other aims.
• We would like to use patients with DBS in VIM thalamus for essential tremor as a control.
• For another study, we will record EEG during tasks in healthy young and middle-aged adults. We will be examining brain circuitry and activity involved with cognitive tasks. We will also be acquiring information from the control young adults' mothers about stress experienced while they were pregnant with their child (the control subjects). The purpose of this study is to examine the relationship between prenatal and early life stress and brain function during adulthood.
• For another study, we will record patient quality of life using questionnaires and interviews after EEG recordings have been completed. This information will then be correlated with prior collected EEGs to assess the relationship between EEG and quality of life in PD patients. We will be recruiting approximately 100 parkinson's patients who have already completed EEG recordings and cognitive tasks for the study for the quality of life project. The prior projects indicate that this amount is enough to discern differences in EEG activity in the regions of concern to establish a relationship between this signal and quality of life surveys.
• For another study, we will study the effects of transcranial Alternating Current Stimulation (HD-tACS) on EEG and behavioral responses. We will do EEG recordings in PD patients during cognitive tasks (the flanker task and the N-back task) and resting condition (as above) during and after tACS. We will be recruiting 24 Parkinson's disease patients.