scholarly journals A Multiscale, Systems-level, Neuropharmacological Model of Cortico-Basal Ganglia System for Arm Reaching under Normal, Parkinsonian and Levodopa Medication Conditions

2021 ◽  
Author(s):  
Sandeep Sathyanandan Nair ◽  
Vignayanandam Ravindernath Muddapu ◽  
V. Srinivasa Chakravarthy
Keyword(s):  
Basal Ganglia ◽  
Success Rate ◽  
Cell Loss ◽  
Drug Dosage ◽  
Biophysical Model ◽  
Substantia Nigra Pars Compacta ◽  
Reaching Task ◽  
Arm Reaching ◽  
Proposed Model ◽  
Cardinal Symptoms

ABSTRACTThe root cause of Parkinson’s disease (PD) is the death of dopaminergic neurons in Substantia Nigra pars compacta (SNc). The exact cause of this cell death is still not known. Loss of SNc cells manifest as the cardinal symptoms of PD, including tremor, rigidity, bradykinesia, and postural imbalance. To investigate the PD condition in detail and understand the link between loss of cells in SNc and PD symptoms, it is important to have an integrated multiscale computational model that can replicate the symptoms at the behavioural level by evoking the key cellular and molecular underlying mechanisms that contribute to the pathology. In line with this objective, we present a multiscale integrated model of cortico-basal ganglia motor circuitry for arm reaching task, incorporating a detailed biophysical model of SNc dopaminergic neuron. Earlier researchers have shown that fluctuations in dopamine (DA) signals are analogous to reward/punishment signals, thereby prompting application of concepts from reinforcement learning (RL) to modelling the basal ganglia system. In our model, we replace the abstract representations of reward with the realistic variable of extracellular DA released by a network of SNc cells and incorporate it with the RL-based behavioural model, which simulates the arm reaching task. Our results showed that as SNc cell loss increases, the percentage success rate to reach the target decreases, and average time to reach the target increases. With levodopa (L-DOPA) medication, both the success rate and the average time to reach the target improved significantly. The proposed model also exhibits how differential dopaminergic axonal degeneration in basal ganglia results in various cardinal symptoms of PD as manifest in reaching movements. From the model results, we were able to show the side effects of L-DOPA mediation, such as wearing off and peak dosage dyskinesias. Moreover, from the results, we were able to predict the optimum dosage for varying degrees of cell loss and L-DOPA medication. The proposed model has a potential clinical application where drug dosage can be optimized as per patient characteristics. We conclude that our model presents a realistic and efficient way of simulating the PD pathology conditions and the effect of levodopa medication, thereby giving a reliable indicator towards the optimization of the drug dosage.

scholarly journals A Multiscale, Systems-Level, Neuropharmacological Model of Cortico-Basal Ganglia System for Arm Reaching Under Normal, Parkinsonian, and Levodopa Medication Conditions

2022 ◽  
Vol 15 ◽  
Author(s):  
Sandeep Sathyanandan Nair ◽  
Vignayanandam Ravindernath Muddapu ◽  
V. Srinivasa Chakravarthy
Keyword(s):  
Basal Ganglia ◽  
Molecular Mechanisms ◽  
Cell Loss ◽  
Patient Characteristics ◽  
Drug Dosage ◽  
Substantia Nigra Pars Compacta ◽  
Reaching Task ◽  
Arm Reaching ◽  
Cardinal Symptoms ◽  
The Impact

In order to understand the link between substantia nigra pars compacta (SNc) cell loss and Parkinson's disease (PD) symptoms, we developed a multiscale computational model that can replicate the symptoms at the behavioural level by incorporating the key cellular and molecular mechanisms underlying PD pathology. There is a modelling tradition that links dopamine to reward and uses reinforcement learning (RL) concepts to model the basal ganglia. In our model, we replace the abstract representations of reward with the realistic variable of extracellular DA released by a network of SNc cells and incorporate it in the RL-based behavioural model, which simulates the arm reaching task. Our results successfully replicated the impact of SNc cell loss and levodopa (L-DOPA) medication on reaching performance. It also shows the side effects of medication, such as wearing off and peak dosage dyskinesias. The model demonstrates how differential dopaminergic axonal degeneration in basal ganglia results in various cardinal symptoms of PD. It was able to predict the optimum L-DOPA medication dosage for varying degrees of cell loss. The proposed model has a potential clinical application where drug dosage can be optimised as per patient characteristics.

scholarly journals Dopamine neurons encode errors in predicting movement trigger occurrence

2015 ◽  
Vol 113 (4) ◽  
pp. 1110-1123 ◽  
Author(s):  
Benjamin Pasquereau ◽  
Robert S. Turner
Keyword(s):  
Hazard Rate ◽  
Dynamic Environment ◽  
Reaction Times ◽  
Dopamine Neurons ◽  
Substantia Nigra Pars Compacta ◽  
Prediction Errors ◽  
Reaching Task ◽  
Foreperiod Duration ◽  
Arm Reaching ◽  
Other Information

The capacity to anticipate the timing of events in a dynamic environment allows us to optimize the processes necessary for perceiving, attending to, and responding to them. Such anticipation requires neuronal mechanisms that track the passage of time and use this representation, combined with prior experience, to estimate the likelihood that an event will occur (i.e., the event's “hazard rate”). Although hazard-like ramps in activity have been observed in several cortical areas in preparation for movement, it remains unclear how such time-dependent probabilities are estimated to optimize response performance. We studied the spiking activity of dopamine neurons in the substantia nigra pars compacta of monkeys during an arm-reaching task for which the foreperiod preceding the “go” signal varied randomly along a uniform distribution. After extended training, the monkeys' reaction times correlated inversely with foreperiod duration, reflecting a progressive anticipation of the go signal according to its hazard rate. Many dopamine neurons modulated their firing rates as predicted by a succession of hazard-related prediction errors. First, as time passed during the foreperiod, slowly decreasing anticipatory activity tracked the elapsed time as if encoding negative prediction errors. Then, when the go signal appeared, a phasic response encoded the temporal unpredictability of the event, consistent with a positive prediction error. Neither the anticipatory nor the phasic signals were affected by the anticipated magnitudes of future reward or effort, or by parameters of the subsequent movement. These results are consistent with the notion that dopamine neurons encode hazard-related prediction errors independently of other information.

scholarly journals Influence of Energy Deficiency on the Molecular Processes of Substantia Nigra Pars Compacta Cell for Understanding Parkinsonian Neurodegeneration: A Comprehensive Biophysical Computational Model

2020 ◽  
Author(s):  
Vignayanandam R. Muddapu ◽  
V. Srinivasa Chakravarthy
Keyword(s):  
Substantia Nigra ◽  
Computational Model ◽  
Cell Loss ◽  
Alpha Synuclein ◽  
Cellular Systems ◽  
Integrated Modelling ◽  
Substantia Nigra Pars Compacta ◽  
Energy Deficiency ◽  
Proposed Model ◽  
Alpha Synuclein Aggregation

ABSTRACTParkinson’s disease (PD) is the second most prominent neurodegenerative disease around the world. Although it is known that PD is caused by the loss of dopaminergic cells in substantia nigra pars compacta (SNc), the decisive cause of this inexorable cell loss is not clearly elucidated. We hypothesize that “Energy deficiency at a sub-cellular/cellular/systems level can be a common underlying cause for SNc cell loss in PD.” Here, we propose a comprehensive computational model of SNc cell which helps us to understand the pathophysiology of neurodegeneration at subcellular level in PD. The proposed model incorporates a rich vein of molecular dynamics related to SNc neurons such as ion channels, active pumps, ion exchangers, dopamine turnover processes, energy metabolism pathways, calcium buffering mechanisms, alpha-synuclein aggregation, Lewy body formation, reactive oxygen species (ROS) production, levodopa uptake, and apoptotic pathways. The proposed model was developed and calibrated based on experimental data. The influx of glucose and oxygen into the model was controlled, and the consequential ATP variations were observed. Apart from this, the dynamics of other molecular players (alpha-synuclein, ROS, calcium, and dopamine) known to play an important role in PD pathogenesis are also studied. The aim of the study was to see how deficits in supply of energy substrates (glucose and oxygen) lead to a deficit in ATP, and furthermore, deficits in ATP are the common factor underlying the pathological molecular-level changes including alpha-synuclein aggregation, ROS formation, calcium elevation, and dopamine dysfunction. The model suggests that hypoglycemia plays a more crucial role in leading to ATP deficits than hypoxia. We believe that the proposed model provides an integrated modelling framework to understand the neurodegenerative processes underlying PD.

Modest Gaze-Related Discharge Modulation in Monkey Dorsal Premotor Cortex During a Reaching Task Performed With Free Fixation

2002 ◽  
Vol 88 (2) ◽  
pp. 1064-1072 ◽  
Author(s):  
Paul Cisek ◽  
John F. Kalaska
Keyword(s):  
Premotor Cortex ◽  
Cell Activity ◽  
Delay Period ◽  
Gaze Direction ◽  
Dorsal Premotor Cortex ◽  
Experimental Conditions ◽  
Reaching Task ◽  
Oculomotor Behavior ◽  
Arm Reaching ◽  
Gaze Angle

Recent studies have shown that gaze angle modulates reach-related neural activity in many cortical areas, including the dorsal premotor cortex (PMd), when gaze direction is experimentally controlled by lengthy periods of imposed fixation. We looked for gaze-related modulation in PMd during the brief fixations that occur when a monkey is allowed to look around freely without experimentally imposed gaze control while performing a center-out delayed arm-reaching task. During the course of the instructed-delay period, we found significant effects of gaze angle in 27–51% of PMd cells. However, for 90–95% of cells, these effects accounted for <20% of the observed discharge variance. The effect of gaze was significantly weaker than the effect of reach-related variables. In particular, cell activity during the delay period was more strongly related to the intended movement expressed in arm-related coordinates than in gaze-related coordinates. Under the same experimental conditions, many cells in medial parietal cortex exhibited much stronger gaze-related modulation and expressed intended movement in gaze-related coordinates. In summary, gaze direction-related modulation of cell activity is indeed expressed in PMd during the brief fixations that occur in natural oculomotor behavior, but its overall effect on cell activity is modest.

Disrupted basal ganglia output during movement preparation in hemi-parkinsonian mice is consistent with behavioral deficits

2021 ◽  
Author(s):  
Anand Tekriwal ◽  
Mario J. Lintz ◽  
John A Thompson ◽  
Gidon Felsen
Keyword(s):  
Basal Ganglia ◽  
Cell Loss ◽  
Motor Deficits ◽  
Movement Preparation ◽  
Rate Model ◽  
Model Framework ◽  
Behavioral Deficits ◽  
Dopaminergic Cell ◽  
Clinical Observations ◽  
External Stimuli

Parkinsonian motor deficits are associated with elevated inhibitory output from the basal ganglia (BG). However, several features of Parkinson's disease (PD) have not been accounted for by this simple "classical rate model" framework, including the observation in PD patients that movements guided by external stimuli are less impaired than otherwise-identical movements generated based on internal goals. Is this difference due to divergent processing within the BG itself, or to the recruitment of extra-BG pathways by sensory processing? In addition, surprisingly little is known about precisely when, in the sequence from selecting to executing movements, BG output is altered by PD. Here, we address these questions by recording activity in the SNr, a key BG output nucleus, in hemiparkinsonian mice performing a well-controlled behavioral task requiring stimulus-guided and internally-specified directional movements. We found that hemiparkinsonian mice exhibited a bias ipsilateral to the side of dopaminergic cell loss that was stronger when movements were internally specified rather than stimulus guided, consistent with clinical observations in parkinsonian patients. We further found that changes in parkinsonian SNr activity during movement preparation were consistent with the ipsilateral behavioral bias, as well as its greater magnitude for internally-specified movements. While these findings are inconsistent with some aspects of the classical rate model, they are accounted for by a related "directional rate model" positing that SNr output phasically over-inhibits motor output in a direction-specific manner. These results suggest that parkinsonian changes in BG output underlying movement preparation contribute to the greater deficit in internally-specified than stimulus-guided movements.

scholarly journals A dynamical model for the basal ganglia-thalamo-cortical oscillatory activity and its implications in Parkinson’s disease

2020 ◽  
Author(s):  
Eva M. Navarro-López ◽  
Utku Çelikok ◽  
Neslihan S. Şengör
Keyword(s):  
Parkinson’S Disease ◽  
Parkinson's Disease ◽  
Basal Ganglia ◽  
Activity Patterns ◽  
Dynamical Model ◽  
Substantia Nigra Pars Compacta ◽  
Oscillatory Activity ◽  
Subcortical Structures ◽  
Neuron Models ◽  
Neuronal Patterns

AbstractWe propose to investigate brain electrophysiological alterations associated with Parkinson’s disease through a novel adaptive dynamical model of the network of the basal ganglia, the cortex and the thalamus. The model uniquely unifies the influence of dopamine in the regulation of the activity of all basal ganglia nuclei, the self-organised neuronal interdependent activity of basal ganglia-thalamo-cortical circuits and the generation of subcortical background oscillations. Variations in the amount of dopamine produced in the neurons of the substantia nigra pars compacta are key both in the onset of Parkinson’s disease and in the basal ganglia action selection. We model these dopamine-induced relationships, and Parkinsonian states are interpreted as spontaneous emergent behaviours associated with different rhythms of oscillatory activity patterns of the basal ganglia-thalamo-cortical network. These results are significant because: (1) the neural populations are built upon single-neuron models that have been robustly designed to have eletrophysiologically-realistic responses, and (2) our model distinctively links changes in the oscillatory activity in subcortical structures, dopamine levels in the basal ganglia and pathological synchronisation neuronal patterns compatible with Parkinsonian states, this still remains an open problem and is crucial to better understand the progression of the disease.

scholarly journals Neuroprotection in Parkinson’s disease: facts and hopes

2019 ◽  
Vol 127 (5) ◽  
pp. 821-829 ◽  
Author(s):  
András Salamon ◽  
Dénes Zádori ◽  
László Szpisjak ◽  
Péter Klivényi ◽  
László Vécsei
Keyword(s):  
Parkinson’S Disease ◽  
Parkinson's Disease ◽  
Cell Loss ◽  
Substantia Nigra Pars Compacta ◽  
Neuroprotective Agents ◽  
Dopaminergic Cell ◽  
Pathological Mechanism ◽  
Positive Results

AbstractParkinson’s disease (PD) is the second most common neurodegenerative disease worldwide. Behind the symptoms there is a complex pathological mechanism which leads to a dopaminergic cell loss in the substantia nigra pars compacta. Despite the strong efforts, curative treatment has not been found yet. To prevent a further cell death, numerous molecules were tested in terms of neuroprotection in preclinical (in vitro, in vivo) and in clinical studies as well. The aim of this review article is to summarize our knowledge about the extensively tested neuroprotective agents (Search period: 1991–2019). We detail the underlying pathological mechanism and summarize the most important results of the completed animal and clinical trials. Although many positive results have been reported in the literature, there is still no evidence that any of them should be used in clinical practice (Cochrane analysis was performed). Therefore, further studies are needed to better understand the pathomechanism of PD and to find the optimal neuroprotective agent(s).

scholarly journals Chronic Stroke Survivors Improve Reaching Accuracy by Reducing Movement Variability at the Trained Movement Speed

2017 ◽  
Vol 31 (6) ◽  
pp. 499-508 ◽  
Author(s):  
Ulrike Hammerbeck ◽  
Nada Yousif ◽  
Damon Hoad ◽  
Richard Greenwood ◽  
Jörn Diedrichsen ◽  
...  
Keyword(s):  
Chronic Phase ◽  
Training Group ◽  
Chronic Stroke ◽  
Movement Speed ◽  
Stroke Survivors ◽  
Movement Variability ◽  
Reaching Task ◽  
Arm Reaching ◽  
Fast Training ◽  
Elbow Movement

Background. Recovery from stroke is often said to have “plateaued” after 6 to 12 months. Yet training can still improve performance even in the chronic phase. Here we investigate the biomechanics of accuracy improvements during a reaching task and test whether they are affected by the speed at which movements are practiced. Method. We trained 36 chronic stroke survivors (57.5 years, SD ± 11.5; 10 females) over 4 consecutive days to improve endpoint accuracy in an arm-reaching task (420 repetitions/day). Half of the group trained using fast movements and the other half slow movements. The trunk was constrained allowing only shoulder and elbow movement for task performance. Results. Before training, movements were variable, tended to undershoot the target, and terminated in contralateral workspace (flexion bias). Both groups improved movement accuracy by reducing trial-to-trial variability; however, change in endpoint bias (systematic error) was not significant. Improvements were greatest at the trained movement speed and generalized to other speeds in the fast training group. Small but significant improvements were observed in clinical measures in the fast training group. Conclusions. The reduction in trial-to-trial variability without an alteration to endpoint bias suggests that improvements are achieved by better control over motor commands within the existing repertoire. Thus, 4 days’ training allows stroke survivors to improve movements that they can already make. Whether new movement patterns can be acquired in the chronic phase will need to be tested in longer term studies. We recommend that training needs to be performed at slow and fast movement speeds to enhance generalization.

Influence of globus pallidus on arm movements in monkeys. II. Effects of stimulation

1984 ◽  
Vol 52 (2) ◽  
pp. 305-322 ◽  
Author(s):  
F. B. Horak ◽  
M. E. Anderson
Keyword(s):  
Basal Ganglia ◽  
Kainic Acid ◽  
Globus Pallidus ◽  
Visual Target ◽  
Reaction Times ◽  
Arm Movements ◽  
Reaction Time Task ◽  
Inhibitory Process ◽  
Arm Reaching ◽  
Sequential Activation

The effect of changing basal ganglia activity with electrical stimulation in and around the globus pallidus (GP) was studied in monkeys trained to make rapid arm-reaching movements to a visual target in a reaction time task. As was the case following kainic acid (KA) lesions of the globus pallidus (30), stimulation changed movement times (MT) without affecting the pattern of sequential activation of muscles involved in the task or, in most cases, the reaction times (RT). Stimulation in the ventrolateral internal segment of the globus pallidus (GPi) or in the ansa lenticularis reduced movement times, whereas stimulation at many sites in the external pallidal segment (GPe), dorsal GPi, and putamen increased movement times for the contralateral arm. These results are consistent with the hypothesis that arm movements are speeded up when the critical output of GPi is increased and arm movements are slowed down when critical GPi output is reduced, either by an inhibitory process (via stimulation-induced activation of inhibitory elements presynaptic to GPi) or by destroying GPi neurons (via kainic acid). The influence of the basal ganglia on the scaling of electromyographic (EMG) amplitude, as opposed to the spatiotemporal organization of EMG activation, is discussed.

Analysis of skill acquisition process: A case study of arm reaching task

2009 ◽  
Vol 57 (2) ◽  
pp. 167-171 ◽  
Author(s):  
Kahori Kita ◽  
Ryu Kato ◽  
Hiroshi Yokoi ◽  
Tamio Arai
Keyword(s):  
Skill Acquisition ◽  
Acquisition Process ◽  
Reaching Task ◽  
Arm Reaching
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