Basal Ganglia and Switching Motor Programs. In: Mckenzie JS, Kemm RE, Wilcock LN, editors. The Basal Ganglia. Boston: Springer US; 1984. pp. 513-44. [DOI: 10.1007/978-1-4684-1212-3_26]

Cortical oscillatory dysfunction in Parkinson disease during movement activation and inhibition

Response activation and inhibition are functions fundamental to executive control that are disrupted in Parkinson disease (PD). We used magnetoencephalography to examine event related changes in oscillatory power amplitude, peak latency and frequency in cortical networks subserving these functions and identified abnormalities associated with PD. Participants (N = 18 PD, 18 control) performed a cue/target task that required initiation of an un-cued movement (activation) or inhibition of a cued movement. Reaction times were variable but similar across groups. Task related responses in gamma, alpha, and beta power were found across cortical networks including motor cortex, supplementary and pre- supplementary motor cortex, posterior parietal cortex, prefrontal cortex and anterior cingulate. PD-related changes in power and latency were noted most frequently in the beta band, however, abnormal power and delayed peak latency in the alpha band in the pre-supplementary motor area was suggestive of a compensatory mechanism. PD peak power was delayed in pre-supplementary motor area, motor cortex, and medial frontal gyrus only for activation, which is consistent with deficits in un-cued (as opposed to cued) movement initiation characteristic of PD.

Basal ganglia hypoactivity during grip force in drug naïve Parkinson's disease

The basal ganglia (BG) are impaired in Parkinson's disease (PD), but it remains unclear which nuclei are impaired during the performance of motor tasks in early-stage PD. Therefore, this study was conducted to determine which nuclei function abnormally, and whether cortical structures are also affected by early-stage PD. The study also determined if cerebellar hyperactivity is found early in the course of PD. Blood oxygenation level dependent activation was compared between 14 early-stage drug-naïve PD patients and 14 controls performing two precision grip force tasks using functional magnetic resonance imaging at 3 T. The grip tasks used in this study were chosen because both tasks are known to provide robust activation in BG nuclei, and the two tasks were similar except that the 2-s task required more switching between contraction and relaxation than the 4-s task. The 4-s task revealed that PD patients were hypoactive relative to controls only in putamen and external globus pallidus, and thalamus. In the 2-s task, PD patients were hypoactive throughout all BG nuclei, thalamus, M1, and supplementary motor area. There were no differences in cerebellar activation between groups during either task. Regions of interest analysis revealed that the hypoactivity observed in PD patients during the 2-s task became more pronounced over time as patients performed the task. This suggests that a motor task that requires switching can accentuate abnormal activity throughout all BG nuclei of early-stage, drug-naive PD, and that the abnormal activity becomes more pronounced with repeated task performance in these patients.

Telencephalon: Neocortex

The neocortex is an ultracomplex, six-layered structure that develops from the dorsal palliai sector of the telencephalic hemispheres (Figs. 2.24, 2.25, 11.1). All mammals, including monotremes and marsupials, possess a neocortex, but in reptiles, i.e. the ancestors of mammals, only a three-layered neocortical primordium is present [509, 511]. The term neocortex refers to its late phylogenetic appearance, in comparison to the “palaeocortical” olfactory cortex and the “archicortical” hippocampal cortex, both of which are present in all amniotes [509].

Movement precues in planning and execution of aiming movements in Parkinson's disease

Two experiments tested how changing a planned movement affects movement initiation and execution in idiopathic Parkinson's disease (PD) patients. In Experiment 1, PD patients, elderly controls, and young adults performed discrete aiming movements to one of two targets on a digitizer. A precue (80% valid cue and 20% invalid cue of all trials) reflecting the subsequent movement direction was presented prior to the imperative stimulus. All groups produced slower reaction times (RTs) to the invalid precue condition. Only the subgroup of patients with slowest movement time showed a significant prolongation of movement for the invalid condition. This suggests that, in the most impaired patients, modifying a planned action also affects movement execution. In Experiment 2, two-segment aiming movements were used to increase the demand on movement planning. PD patients and elderly controls underwent the two precue conditions (80% valid, 20% invalid). Patients exhibited longer RTs than the controls. RT was similarly increased for the invalid condition in both groups. The patients, however, exhibited longer movement times, lower peak velocities, and higher normalized jerk scores of the first segment in the invalid condition compared to the valid condition. Conversely, the controls showed no difference between the valid and invalid cue conditions. Thus, PD patients demonstrated substantially pronounced movement slowness and variability when required to change a planned action. The results from both experiments suggest that modifying a planned action may continue beyond the initiation phase into the execution phase in PD patients.

The Importance of Graft Placement and Task Complexity for Transplant-Induced Recovery of Simple and Complex Sensorimotor Deficits in Dopamine Denervated Rats

The present study examined the role of graft placement and behavioural task complexity in determining the functional efficacy of intrastriatal grafts of dopamine-rich fetal ventral mesencephalon (VM) placed in the dopamine (DA) depleted striatum. The functional effects of two different striatal placements of VM grafts were evaluated using tests of drug-induced motor asymmetry, simple sensorimotor orienting response, and a more complex sensorimotor integrative task (disengage behaviour), in which the rat has to perform the orienting response while in the act of eating. Rats with complete unilateral 6-hydroxydopamine (6-OHDA) lesions of the mesostriatal DA pathway, received either implants of dissociated fetal VM in the central or ventrolateral portions of the denervated striatum. Nongrafted lesioned rats served as controls. Nine weeks after grafting, the rats were tested on separate days for disengage behaviour, sensorimotor orientation, and amphetamine-induced rotational behaviour. Consistent with previous findings, the two graft placements had differential effects on drug-induced motor asymmetry and sensorimotor responses: the centrally placed VM grafts reversed amphetamine-induced rotational asymmetry but had little effect on the sensorimotor deficit, whereas the ventrolaterally placed grafts reversed the sensorimotor orientation deficits without any effect on the drug-induced rotation. In contrast, fetal VM grafts, regardless of their placement, did not ameliorate the observed deficits in disengage behaviour; that is the grafted rats that had recovered their sensorimotor response in the absence of food were unable to perform the same orienting response while eating. These results provide evidence that functional intrastriatal VM grafts which are capable of restoring sensorimotor responses or motor asymmetry fail to affect lesion-induced deficits in a task that requires more complex sensorimotor integration. It is suggested that the degree of anatomical integration of the grafted DA neurons into the host circuitry will determine the efficacy of the grafts to influence more complex sensorimotor integrative deficits in the DA lesion model.

Collective responses of neostriatal (putamen) neurons during alternative behavior in monkeys

A monkey (Macaca nemestrina) was trained to perform a behavioral program consisting of the selection and execution of a defined sequence of actions according to a visual conditioned signal. Discriminant analysis was used to evaluate the parameters of the collective activity of six simultaneously recorded putamen neurons. The collective activity of the neurons showed significant differences associated with execution by the monkey of left- and right-sided tasks. These differences were seen to be quite consistent in different groups of neurons. Despite the fact that putamen neurons were involved in the performance of nine separately analyzed fragments of the program, differences were seen in two of these: at the moment of taking the decision relating to the direction of movement, and after its completion when a signal indicating the completed result was presented, independently of whether the animal selected the side for the action correctly or incorrectly. In the case of erroneous decisions, the response mosaic differed from that obtained for correct decisions; however, differences due to previously taken decisions regarding the side of action were preserved. These differences were greater at the point of program completion than at the moment of deciding the direction of movement.

The switching model of latent inhibition: an update of neural substrates

Organisms exposed to a stimulus which has no significant consequences, show subsequently latent inhibition (LI), namely, retarded conditioning to this stimulus. LI is considered to index the capacity to ignore irrelevant stimuli and its disruption has recently received increasing interest as an animal model of cognitive deficits in schizophrenia. Initial studies indicated that LI is disrupted by systemic or intra-accumbens injections of amphetamine and hippocampal lesions, and potentiated by systemic administration of neuroleptics. On the basis of these findings, the switching model of LI proposed that LI depends on the subicular input to the nucleus accumbens (NAC). Subsequent studies supported and refined this proposition. Lesion studies show that LI is indeed disrupted by severing the subicular input to the NAC, and further implicate the entorhinal/ventral subicular portion of this pathway projecting to the shell subterritory of the NAC. There is a functional dissociation between the shell and core subterritories of the NAC, with lesions of the former but not of the latter disrupting LI. This suggests that the shell is necessary for the expression and the core for the disruption of LI. The involvement of the NAC has been also demonstrated by findings that LI is disrupted by intra-accumbens injection of amphetamine and potentiated by DA depletion or blockade in this structure. Disruption and potentiation of LI by systemic administration of amphetamine and neuroleptics, respectively, have been firmly established, and in addition, have been shown to be sensitive to parametric manipulations of the LI procedure. LI is unaffected by lesions and DA manipulations of medial prefrontal cortex and lesions of basolateral amygdala. The implications of these findings for LI as an animal model of schizophrenia are discussed.

The role of the striatum in motor learning: dissociations between isometric motor control processes in Parkinson's disease

Studies of Parkinson's disease (PD) have been used to support the hypothesis that the striatum serves procedural learning but interpretation of the results is confounded by extra-striate pathology and coincidental non-procedural cognitive deficits. The motor deficit of PD involves particularly internally cued movement, without visual feedback, because of disruption to frontostriatal circuits. Thus, we used a non-visual isometric task as a sensitive measure of motor learning in early non-demented patients with PD and examined the effects of dopamine replacement. The PD group showed disproportionate under-shooting of the target but normal motor learning. Learning correlated with some cognitive measures but not clinical motor disability or depression. Treatment had no effect on performance, despite clinical improvement. The results indicate dissociations between motor control processes resulting from striatal pathology. Putaminal circuits are involved in force generation and prediction but not critically in motor learning.

Turnover of dopamine and serotonin and their metabolites in the striatum of aged rats

Turnover of dopamine (DA), serotonin [5-hydroxytryptamine (5-HT)], and their metabolites has been measured in adult and aged rats. Turnover rates of 3,4-dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA), and 5-hydroxy-3-indoleacetic acid (5-HIAA) have been assayed from the disappearance rates after blocking by pargyline inhibition of monoamine oxidase (MAO) and from the accumulation rates by probenecid inhibition of the probenecid-sensitive transport system. DA and 5-HT turnover rates have been measured as accumulation rates of 3,4-dihydroxyphenylalanine and 5-hydroxytryptophan, respectively, after central decarboxylase inhibition by 3-hydroxybenzylhydrazine (NSD-1015) and as accumulation rates of DA and 5-HT after pargyline inhibition of MAO. The DA turnover rate after NSD-1015 was 23.9% lower in aged rats than in adults, whereas after pargyline there was no significant difference between the two age groups. The HVA fractional rate constant and turnover after pargyline were lower in aged rats than in adults, and HVA turnover after probenecid was higher in aged rats than in adults. The DOPAC-HVA pathway seems to be reinforced at the expense of DOPAC conjugation. In aged and adult rats whose 5-HT steady-state levels were not statistically different, the 5-HT turnover rate after pargyline and NSD-1015 treatment was lower in aged rats than in adults. An increase of 5-HIAA levels after pargyline and probenecid treatment in aged rats could be due to the handling stress.

The participation of mediator and peptidergic systems of the brain in conditioned reflex mechanisms

New data on the significance of mediator and peptidergic systems of the striatal level in the organization of alimentary conditioned reflexes are presented in this report. The role of acetylcholine-, dopamine-, GABA-and P-ergic systems of the caudate nucleus and the amygdala in the realization of positive and negative conditioned reflexes was investigated. The experiments were carried out on dogs with chemotrodes and microelectrodes implanted in subcortical structures. The results of the experiments with microinjections of the relevant substances into individual subcortical structures showed that activation of the same mediator system in various structures may lead to both unidirectional and multidirectional behavioral effects. On the other hand, the activation of various subcortical mediator systems can lead to identical changes in conditioned reflex activity. The effect of the administration of activators or blockers of a subcortical mediator system depends in many ways on the functional state of the nervous system at the moment of administration and on the localization of the microinjection. It is difficult to predict beforehand the role of various subcortical structures in the organization of integrated behavioral acts. The question of the necessity of studying mediator and peptidergic systems of each subcortical structure in order to understand their significance in the mechanisms of the conditioned reflex is raised.

The programming and execution of movement sequences in Parkinson's disease

Parkinsonian and neurologically normal subjects performed a finger-tapping task in which different sequence lengths had to be executed as rapidly as possible. For each response sequence, reaction time (RT), inter-tap-intervals (ITIs) and error patterns were recorded. It was found that the RT-sequence length relationship as well as the group ITI data were different for the two groups, indicative of impaired programming in the Parkinsonian subjects. This conclusion was supported by a relative dissociation of the first and subsequent taps and by a pattern of progressively increasing errors with longer tap sequences in the Parkinsonians.