Effect of Dexmedetomidine on Perception of Paresthesia during Subthalamic Nucleus Deep Brain Stimulation Surgery for Parkinson's Disease.

Background: Deep brain stimulation (DBS) has become a well-established treatment for the management of Parkinson's disease (PD). The most common method of lead targeting utilizes microelectrode recording (MER) and intraoperative macrostimulation to confirm accurate placement of the lead. This has been significantly aided by the use of dexmedetomidine (DEX) sedation during the procedure. Despite the frequent use of DEX, it has been theorized that DEX may have some effects on the MER during intraoperative testing. The effect on the perception of sensory thresholds during macrostimulation in the form of paresthesia is still unreported. Objectives: To investigate the effect of the sedative DEX on sensory perception thresholds observed in the intraoperative versus postoperative settings for patients undergoing subthalamic nucleus (STN) DBS surgery for PD. Materials and Methods: Adult patients (n = 8) with a diagnosis of PD underwent placement of DBS leads (n = 14) in the STN. Patients were subjected to intraoperative macrostimulation for capsular and sensory thresholds prior to placement of each DBS lead. These were compared to sensory thresholds observed in the postoperative setting during outpatient programming at three depths on each lead (n = 42). Results: In most contacts (22/42) (P = 0.19), sensory thresholds for paresthesia perception were either perceived at a higher voltage or absent during intraoperative testing in comparison to those observed in the postoperative setting. Conclusions: DEX appears to have measurable (though not statistically significant) effect on the perception of paresthesia observed during intraoperative testing.

Direct Comparison of Posterior Subthalamic Area Stimulation versus Subthalamic Nucleus Deep Brain Stimulation in Parkinson's Disease.

In this case report, we describe successful tremor capture via stimulation of the posterior subthalamic area (PSA) for a patient with tremor-predominant Parkinson's disease. In this scenario, the patient had a deep brain stimulation (DBS) lead placed in the PSA of the right hemisphere and a DBS lead placed in the subthalmic nucleus (STN) of the left hemisphere. Therefore, we were able to directly compare tremor capture in the same patient receiving stimulation in two different brain areas. We show that both placements are equally efficacious for tremor suppression, though the DBS lead placed in the PSA required slightly higher current intensity. This comparison in the same patient confirms that stimulation of the PSA can successfully suppress tremor in Parkinson's disease.

Predicting extended hospital stay after deep brain stimulation surgery in Parkinson's patients.

BACKGROUND: The goal of deep brain stimulation (DBS) is to achieve maximal benefit for the patient while minimizing the likelihood of adverse effects. Currently, no standardized criteria exist that predicts extended hospital stay in DBS patients, although careful patient selection is recognized as a very important step for successful DBS therapy. OBJECTIVES AND METHODS: The objective of this study was to identify eight key factors that predicted extended post-operative hospital stay following DBS lead implantation, in an effort to better identify patients that would require minimal hospital stay, resulting in reduced cost and reduced exposure to hospital- related problems. Univariate logistic regression models were used to examine associations between each factor and patients' post-surgical outcomes. RESULTS: Using data collected from 183 patients, we found that 53 patients required a hospital stay longer than two days within one month post-procedure. Those who were 70 years or older and those who had frequent falls were significantly more likely to require extended post-surgical care. Patients that scored three points or higher on our eight-factor assessment scale had a greater likelihood of experiencing an event that would require an extended hospital stay following DBS lead placement, regardless of what three factors were present. CONCLUSIONS: Any PD patient who is 70 years or older, incurring frequent falls, or with more than three points on our scale, should be carefully screened and cautioned about likely prolonged recovery and extended post-operative hospital stay.

Anatomic Review of the Ventral Capsule/Ventral Striatum and the Nucleus Accumbens to Guide Target Selection for Deep Brain Stimulation for Obsessive-Compulsive Disorder.

BACKGROUND: Disturbances in the reward network of the brain underlie addiction, depression, and obsessive-compulsive disorder. The ventral capsule/ventral striatum and nucleus accumbens (NAc) region is a clinically approved target for deep brain stimulation for obsessive-compulsive disorder. METHODS: We performed a comprehensive literature review to define clinically relevant anatomy and connectivity of the ventral capsule/ventral striatum and NAc region to guide target selection for deep brain stimulation. RESULTS: Architecturally and functionally, the NAc is divided into the core and the shell, with each area having different connections. The shell primarily receives limbic information, and the core typically receives information from the motor system. In general, afferents from the prefrontal cortex, hippocampus, and amygdala are excitatory. The dopaminergic projections to the NAc from the ventral tegmental area modulate the balance of these excitatory inputs. Several important inputs to the NAc converge at the junction of the internal capsule (IC) and the anterior commissure (AC): the ventral amygdalofugal pathways that run parallel to and underneath the AC, the precommissural fornical fibers that run anterior to the AC, axons from the ventral prefrontal cortex and medial orbitofrontal cortex that occupy the most ventral part of the IC and embedding within the NAc and AC, and the superolateral branch of the medial forebrain bundle located parallel to the anterior thalamic radiation in the IC. CONCLUSIONS: The caudal part of the NAc passing through the IC-AC junction may be an effective target for deep brain stimulation to improve behavioral symptoms associated with obsessive-compulsive disorder.

Cortical projections to the superior colliculus in grey squirrels (Sciurus carolinensis).

The superior colliculus is an important midbrain structure involved with integrating information from varying sensory modalities and sending motor signals to produce orienting movements towards environmental stimuli. Because of this role, the superior colliculus receives a multitude of sensory inputs from a wide variety of subcortical and cortical structures. Proportionately, the superior colliculus of grey squirrels is among the largest in size of all studied mammals, suggesting the importance of this structure in the behavioural characteristics of grey squirrels. Yet, our understanding of the connections of the superior colliculus in grey squirrels is lacking, especially with respect to possible cortical influences. In this study, we placed anatomical tracer injections within the medial aspect of the superior colliculus of five grey squirrels (Sciurus carolinensis) and analysed the areal distribution of corticotectal projecting cells in flattened cortex. V1 projections to the superior colliculus were studied in two additional animals. Our results indicate that the superior colliculus receives cortical projections from visual, higher order somatosensory, and higher order auditory regions, as well as limbic, retrosplenial and anterior cingulate cortex. Few, if any, corticotectal projections originate from primary motor, primary somatosensory or parietal cortical regions. This distribution of inputs is similar to the distribution of inputs described in other rodents such as rats and mice, yet the lack of inputs from primary somatosensory and motor cortex is features of corticotectal inputs more similar to those observed in tree shrews and primates, possibly reflecting a behavioural shift from somatosensory (vibrissae) to visual navigation.

Distributions of Cells and Neurons across the Cortical Sheet in Old World Macaques.

According to previous research, cell and neuron densities vary across neocortex in a similar manner across primate taxa. Here, we provide a more extensive examination of this effect in macaque monkeys. We separated neocortex from the underlying white matter in 4 macaque monkey hemispheres (1 Macaca nemestrina, 2 Macaca radiata, and 1 Macaca mulatta), manually flattened the neocortex, and divided it into smaller tissue pieces for analysis. The number of cells and neurons were determined for each piece across the cortical sheet using flow cytometry. Primary visual cortex had the most densely packed neurons and primary motor cortex had the least densely packed neurons. With respect to differences in brain size between cases, there was little variability in the total cell and neuron numbers within specific areas, and overall trends were similar to what has been previously described in Old World baboons and other primates. The average hemispheric total cell number per hemisphere ranged from 2.9 to 3.7 billion, while the average total neuron number ranged from 1.3 to 1.7 billion neurons. The visual cortex neuron densities were predictably higher, ranging from 18.2 to 34.7 million neurons/cm2 in macaques, in comparison to a range of 9.3-17.7 million neurons/cm2 across cortex as a whole. The results support other evidence that neuron surface densities vary across the cortical sheet in a predictable pattern within and across primate taxa.

Cortical cell and neuron density estimates in one chimpanzee hemisphere.

The density of cells and neurons in the neocortex of many mammals varies across cortical areas and regions. This variability is, perhaps, most pronounced in primates. Nonuniformity in the composition of cortex suggests regions of the cortex have different specializations. Specifically, regions with densely packed neurons contain smaller neurons that are activated by relatively few inputs, thereby preserving information, whereas regions that are less densely packed have larger neurons that have more integrative functions. Here we present the numbers of cells and neurons for 742 discrete locations across the neocortex in a chimpanzee. Using isotropic fractionation and flow fractionation methods for cell and neuron counts, we estimate that neocortex of one hemisphere contains 9.5 billion cells and 3.7 billion neurons. Primary visual cortex occupies 35 cm(2) of surface, 10% of the total, and contains 737 million densely packed neurons, 20% of the total neurons contained within the hemisphere. Other areas of high neuron packing include secondary visual areas, somatosensory cortex, and prefrontal granular cortex. Areas of low levels of neuron packing density include motor and premotor cortex. These values reflect those obtained from more limited samples of cortex in humans and other primates.

Transcranial magnetic stimulation for chronic pain.

Current data suggest that transcranial magnetic stimulation (TMS) has the potential to be an effective and complimentary treatment modality for patients with chronic neuropathic pain syndromes. The success of TMS for pain relief depends on the parameters of the stimulation delivered, the location of neural target, and duration of treatment. TMS can be used to excite or inhibit underlying neural tissue that depends on long-term potentiation and long-term depression, respectively. Long-term randomized controlled studies are warranted to establish the efficacy of repetitive TMS in patients with various chronic pain syndromes.

Three counting methods agree on cell and neuron number in chimpanzee primary visual cortex.

Determining the cellular composition of specific brain regions is crucial to our understanding of the function of neurobiological systems. It is therefore useful to identify the extent to which different methods agree when estimating the same properties of brain circuitry. In this study, we estimated the number of neuronal and non-neuronal cells in the primary visual cortex (area 17 or V1) of both hemispheres from a single chimpanzee. Specifically, we processed samples distributed across V1 of the right hemisphere after cortex was flattened into a sheet using two variations of the isotropic fractionator cell and neuron counting method. We processed the left hemisphere as serial brain slices for stereological investigation. The goal of this study was to evaluate the agreement between these methods in the most direct manner possible by comparing estimates of cell density across one brain region of interest in a single individual. In our hands, these methods produced similar estimates of the total cellular population (approximately 1 billion) as well as the number of neurons (approximately 675 million) in chimpanzee V1, providing evidence that both techniques estimate the same parameters of interest. In addition, our results indicate the strengths of each distinct tissue preparation procedure, highlighting the importance of attention to anatomical detail. In summary, we found that the isotropic fractionator and the stereological optical fractionator produced concordant estimates of the cellular composition of V1, and that this result supports the conclusion that chimpanzees conform to the primate pattern of exceptionally high packing density in V1. Ultimately, our data suggest that investigators can optimize their experimental approach by using any of these counting methods to obtain reliable cell and neuron counts.

Histological features of layers and sublayers in cortical visual areas V1 and V2 of chimpanzees, macaque monkeys, and humans.

The layers and sublayers of primary visual cortex, or V1, in primates are easily distinguishable compared to those in other cortical areas, and are especially distinct in anthropoid primates - monkeys, apes, and humans - where they also vary in histological appearance. This variation in primate-specific specialization has led to a longstanding confusion over the identity of layer 4 and its proposed sublayers in V1. As the application of different histological markers relate to the issue of defining and identifying layers and sublayers, we applied four traditional and four more recent histological markers to brain sections of V1 and adjoining secondary visual cortex (V2) in macaque monkeys, chimpanzees, and humans in order to compare identifiable layers and sublayers in both cortical areas across these species. The use of Nissl, neuronal nuclear antigen (NeuN), Gallyas myelin, cytochrome oxidase (CO), acetylcholinesterase (AChE), nonphosphorylated neurofilament H (SMI-32), parvalbumin (PV), and vesicular glutamate transporter 2 (VGLUT2) preparations support the conclusion that the most popular scheme of V1 lamination, that of Brodmann, misidentifies sublayers of layer 3 (3Bß and 3C) as sublayers of layer 4 (4A and 4B), and that the specialized sublayer of layer 3 in monkeys, 3Bß, is not present in humans. These differences in interpretation are important as they relate to the proposed functions of layer 4 in primate species, where layer 4 of V1 is a layer that receives and processes information from the visual thalamus, and layer 3 is a layer that transforms and distributes information to other cortical areas.

Epileptic baboons have lower numbers of neurons in specific areas of cortex.

Epilepsy is characterized by recurrent seizure activity that can induce pathological reorganization and alter normal function in neocortical networks. In the present study, we determined the numbers of cells and neurons across the complete extent of the cortex for two epileptic baboons with naturally occurring seizures and two baboons without epilepsy. Overall, the two epileptic baboons had a 37% average reduction in the number of cortical neurons compared with the two nonepileptic baboons. The loss of neurons was variable across cortical areas, with the most pronounced loss in the primary motor cortex, especially in lateral primary motor cortex, representing the hand and face. Less-pronounced reductions of neurons were found in other parts of the frontal cortex and in somatosensory cortex, but no reduction was apparent in the primary visual cortex and little in other visual areas. The results provide clear evidence that epilepsy in the baboon is associated with considerable reduction in the numbers of cortical neurons, especially in frontal areas of the cortex related to motor functions. Whether or not the reduction of neurons is a cause or an effect of seizures needs further investigation.

Cell and neuron densities in the primary motor cortex of primates.

Cell and neuron densities vary across the cortical sheet in a predictable manner across different primate species (Collins et al., 2010b). Primary motor cortex, M1, is characterized by lower neuron densities relative to other cortical areas. M1 contains a motor representation map of contralateral body parts from tail to tongue in a mediolateral sequence. Different functional movement representations within M1 likely require specialized microcircuitry for control of different body parts, and these differences in circuitry may be reflected by variation in cell and neuron densities. Here we determined cell and neuron densities for multiple sub-regions of M1 in six primate species, using the semi-automated flow fractionator method. The results verify previous reports of lower overall neuron densities in M1 compared to other parts of cortex in the six primate species examined. The most lateral regions of M1 that correspond to face and hand movement representations, are more neuron dense relative to medial locations in M1, which suggests differences in cortical circuitry within movement zones.

Use of flow cytometry for high-throughput cell population estimates in brain tissue.

The large size of primate brains is an impediment to obtaining high-resolution cell number maps of the cortex in humans and non-human primates. We present a rapid, flow cytometry-based cell counting method that can be used to estimate cell numbers from homogenized brain tissue samples comprising the entire cortical sheet. The new method, called the flow fractionator, is based on the isotropic fractionator (IF) method (Herculano-Houzel and Lent, 2005), but substitutes flow cytometry analysis for manual, microscope analysis using a Neubauer counting chamber. We show that our flow cytometry-based method for total cell estimation in homogenized brain tissue provides comparable data to that obtained using a counting chamber on a microscope. The advantages of the flow fractionator over existing methods are improved precision of cell number estimates and improved speed of analysis.

Development of motor maps in rats and their modulation by experience.

While a substantial literature demonstrates the effect of differential experience on development of mammalian sensory cortices and plasticity of adult motor cortex, characterization of differential experience on the functional development of motor cortex is meager. We first determined when forelimb movement representations (motor maps) could be detected in rats during postnatal development and then whether their motor map expression could be altered with rearing in an enriched environment consisting of group housing and novel toys or skilled learning by training on the single pellet reaching task. All offspring had high-resolution intracortical microstimulation (ICMS)-derived motor maps using methodologies previously optimized for the adult rat. First, cortical GABA-mediated inhibition was depressed by bicuculline infusion directly into layer V of motor cortex and ICMS-responsive points were first reliably detected on postnatal day (PND) 13. Without relying on bicuculline disinhibition of cortex, motor maps emerged on PND 35 and then increased in size until PND 60 and had progressively lower movement thresholds. Second, environmental enrichment did not affect initial detection of responsive points and motor maps in non-bicuculline-treated pups on PND 35. However, motor maps were larger on PND 45 in enriched rat pups relative to pups in the standard housing condition. Rats in both conditions had similar map sizes on PNDs 60, 75, and 90. Third, reach training in rat pups resulted in an internal reorganization of the map in the hemisphere contralateral, but not ipsilateral, to the trained forelimb. The map reorganization was expressed as proportionately more distal (digit and wrist) representations on PND 45. Our data indicate that both environmental enrichment and skilled reach training experience can differentially modify expression of motor maps during development.

Optimal parameters for microstimulation derived forelimb movement thresholds and motor maps in rats and mice.

Intracortical microstimulation (ICMS) is a technique that was developed to derive movement representations (motor maps) of the motor cortex, and was originally used in cats and the capuchin monkey. In more modern experiments, ICMS has been used in rats and mice to assess and interpret plasticity of motor maps in response to experimental manipulation; however, a systematic determination of the optimal ICMS parameters necessary to derive baseline motor maps in rats and mice has not been published. In the present manuscript, we describe two experiments. We first determined the optimal stimulation frequency, pulse number, neocortical depth, and current polarity to achieve the minimum current intensity (movement threshold) to elicit forelimb movements in rats and mice. We show that experimentally naïve rats and mice differ on several of these ICMS parameters. In the second experiment, we measured movement thresholds and map size in states of enhanced neocortical inhibition by the administration of diazepam, as well as neocortical sensitization as the result of repeated seizures. We conclude that movement thresholds are inversely related to motor map size, and that treatments result in a widespread shift the balance between excitation and inhibition in motor neocortical layer 5 influences both movement thresholds and map size.

Neuron densities vary across and within cortical areas in primates.

The numbers and proportion of neurons in areas and regions of cortex were determined for a single cortical hemisphere from two prosimian galagos, one New World owl monkey, one Old World macaque monkey, and one baboon. The results suggest that there is a common plan of cortical organization across the species examined here and also differences that suggest greater specializations in the Old World monkeys. In all primates examined, primary visual cortex (V1) was the most neuron-dense cortical area and the secondary visual areas had higher-than-average densities. Primary auditory and somatosensory areas tended to have high densities in the Old World macaque and baboon. Neuronal density varies less across cortical areas in prosimian galagos than in the Old World monkeys. Thus, cortical architecture varies greatly within and across primate species, but cell density is greater in cortex devoted to the early stages of sensory processing.

Seizures, but not lowered seizure thresholds, results in larger neocortical motor maps and concomitant disruptions in skilled motor behaviour.

Kindling of the sensorimotor neocortex has been found to result in reorganization of the somatotopic map of movement representations as well as disruptions of skilled forelimb behaviours. It has been suggested that the repeated seizures induced during kindling altered motor maps, thereby disrupting the motor engram necessary for the production of skilled movements. However, kindling leads to neural changes other than those associated with repeated seizures, and the role of these comorbid effects is often overlooked. Our lab has developed a stimulation paradigm, which allows for the dissociation of the two main effects of kindling; repeated seizures and the reduction of afterdischarge (seizure) threshold. In the current study, we have utilized this paradigm to examine the effects of electrical stimulation on motor maps and skilled forelimb behaviour. We found that repeated seizures with no concomitant reduction of afterdischarge threshold resulted in large motor maps, as well as task specific deficits in skilled forelimb use and deficiencies in task acquisition. Rats that had reduced seizure thresholds and few seizures did not show alterations in map size or skilled forelimb use. These results suggest that movement disturbances following kindling are the result of repeated seizures, and not other stimulation-induced effects such as reduction of afterdischarge threshold. These results also corroborate the relationship between the integrity of movement representations and the ability to perform skilled motor tasks.

A rapid and reliable method of counting neurons and other cells in brain tissue: a comparison of flow cytometry and manual counting methods.

It is of critical importance to understand the numbers and distributions of neurons and non-neurons in the cerebral cortex because cell numbers are reduced with normal aging and by diseases of the CNS. The isotropic fractionator method provides a faster way of estimating numbers of total cells and neurons in whole brains and dissected brain parts. Several comparative studies have illustrated the accuracy and utility of the isotropic fractionator method, yet it is a relatively new methodology, and there is opportunity to adjust procedures to optimize its efficiency and minimize error. In the present study, we use 142 samples from a dissected baboon cortical hemisphere to evaluate if isotropic fractionator counts using a Neubauer counting chamber and fluorescence microscopy could be accurately reproduced using flow cytometry methods. We find greater repeatability in flow cytometry counts, and no evidence of constant or proportional bias when comparing microscopy to flow cytometry counts. We conclude that cell number estimation using a flow cytometer is more efficient and more precise than comparable counts using a Neubauer chamber on a fluorescence microscope. This method for higher throughput, precise estimation of cell numbers has the potential to rapidly advance research in post-mortem human brains and vastly improve our understanding of cortical and subcortical structures in normal, injured, aged, and diseased brains.

Motor map expansion in the pilocarpine model of temporal lobe epilepsy is dependent on seizure severity and rat strain.

Functional alterations in movement representations (motor maps) have been observed in some people with epilepsy and, under experimental control, electrically-kindled seizures in rats also result in persistently larger motor maps. To determine if a single event of status epilepticus and its latent consequences can affect motor map expression, we assessed forelimb motor maps in rats using the pilocarpine model of temporal lobe epilepsy. We examined both pilocarpine-induced seizures, and status epilepticus (SE) in two strains that differ in their propensity for epileptogenesis; Wistar and Long-Evans. Pilocarpine was administered intraperitoneally at dosages that resulted in equivalent proportions of seizures, SE, and survival in both strains. Rats from both strains were given saline injections as a control. Diazepam was administered to all rats to attenuate seizure activity and promote survival. All rats had high-resolution movement representations derived using standard intracortical microstimulation methodologies at 48 h, 1 week, or 3 weeks following treatment. Pilocarpine-induced seizures only gave rise to motor map enlargement in Wistar rats, which also showed interictal spiking, and only at 3 weeks post-treatment indicating altered motor map expression in this strain following a latent or maturational period. Pilocarpine-induced SE yielded larger motor maps at all time points in Wistar rats but only a transient (48 h) map expansion in Long-Evans rats. Our results demonstrate that seizures and SE induced by a convulsant agent alter the functional expression of motor maps that is dependent on seizure severity and a genetic (strain) predisposition to develop epileptiform events.

Functional brain mapping at 9.4T using a new MRI-compatible electrode chronically implanted in rats.

There is a need for acute and chronic stimulation of the brain within the MRI for studies of epilepsy, as well as deep brain stimulation for movement and behavioral disorders. This work describes the production and characteristics of carbon fiber-based electrodes for acute and chronic stimulation in the brain. Increasing MRI field strengths are making it increasingly difficult to introduce foreign objects without a susceptibility artifact. We describe the production of, and the characteristics of carbon fiber-based electrodes. These are biocompatible and can be implanted for chronic studies. We show the use of these electrodes at 9.4T for studying functional activation. Data are presented showing regional connectivity. Activation not only occurs near the electrode, but at sites distant and often contralateral to the electrode. In addition, there were sites showing strong negative activation to stimulation both with direct stimulation and during a kindling-associated seizure.