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Background: Deep brain stimulation (DBS) of the subthalamic region is an established therapy for advanced Parkinson's disease (PD). However, patients often require time-intensive post-operative management to balance their coupled stimulation and medication treatments. Given the large and complex parameter space associated with this task, we propose that clinical decision support systems (CDSS) based on machine learning algorithms could assist in treatment optimization. Objective: Develop a proof-of-concept implementation of a CDSS that incorporates patient-specific details on both stimulation and medication. Methods: Clinical data from 10 patients, and 89 post-DBS surgery visits, were used to create a prototype CDSS. The system was designed to provide three key functions: 1) information retrieval; 2) visualization of treatment, and; 3) recommendation on expected effective stimulation and drug dosages, based on three machine learning methods that included support vector machines, Naïve Bayes, and random forest. Results: Measures of medication dosages, time factors, and symptom-specific pre-operative response to levodopa were significantly correlated with post-operative outcomes (P

High-frequency deep brain stimulation (DBS) of the thalamus or basal ganglia represents an effective clinical technique for the treatment of several medically refractory movement disorders (e.g., Parkinson's disease, essential tremor, and dystonia). In addition, new clinical applications of DBS for other neurologic and psychiatric disorders (e.g., epilepsy and obsessive-compulsive disorder) have been vaulted forward. Although DBS has been effective in the treatment of movement disorders and is rapidly being explored for the treatment of other neurologic disorders, the scientific understanding of its mechanisms of action remains unclear and continues to be debated in the scientific community. Optimization of DBS technology for present and future therapeutic applications will depend on identification of the therapeutic mechanism(s) of action. The goal of this review is to address the present knowledge of the effects of high frequency stimulation within the central nervous system and comment on the functional implications of this knowledge for uncovering the mechanism(s) of DBS. Four general hypotheses have been developed to explain the mechanism(s) of DBS: depolarization blockade, synaptic inhibition, synaptic depression, and stimulation-induced modulation of pathologic network activity. Using the results from microdialysis, neural recording, functional imaging, and neural modeling experiments, the authors address the main hypotheses and attempt to reconcile what have been considered conflicting results from different research modalities.

OBJECTIVE Do movements made with an intracortical BCI (iBCI) have the same movement time properties as able-bodied movements? Able-bodied movement times typically obey Fitts' law: [Formula: see text] (where MT is movement time, D is target distance, R is target radius, and [Formula: see text] are parameters). Fitts' law expresses two properties of natural movement that would be ideal for iBCIs to restore: (1) that movement times are insensitive to the absolute scale of the task (since movement time depends only on the ratio [Formula: see text]) and (2) that movements have a large dynamic range of accuracy (since movement time is logarithmically proportional to [Formula: see text]). APPROACH Two participants in the BrainGate2 pilot clinical trial made cortically controlled cursor movements with a linear velocity decoder and acquired targets by dwelling on them. We investigated whether the movement times were well described by Fitts' law. MAIN RESULTS We found that movement times were better described by the equation [Formula: see text], which captures how movement time increases sharply as the target radius becomes smaller, independently of distance. In contrast to able-bodied movements, the iBCI movements we studied had a low dynamic range of accuracy (absence of logarithmic proportionality) and were sensitive to the absolute scale of the task (small targets had long movement times regardless of the [Formula: see text] ratio). We argue that this relationship emerges due to noise in the decoder output whose magnitude is largely independent of the user's motor command (signal-independent noise). Signal-independent noise creates a baseline level of variability that cannot be decreased by trying to move slowly or hold still, making targets below a certain size very hard to acquire with a standard decoder. SIGNIFICANCE The results give new insight into how iBCI movements currently differ from able-bodied movements and suggest that restoring a Fitts' law-like relationship to iBCI movements may require non-linear decoding strategies.

Deep brain stimulation (DBS) is an established therapy for the management of advanced Parkinson's disease (PD). However, the coupled adjustment of pharmacologic therapy and stimulation parameter settings is a time-consuming process and treatment outcomes are not always optimal. In this study, we develop a linear function that relates the DBS parameters, the levodopa dosage, and patient-specific preoperative clinical data with the actual treatment motor outcomes. To this end, we incorporate image-based patient-specific computer models of the volume of tissue activated by DBS in a multilinear regression analysis (6 PD patients; 60 follow up visits). The resulting predictor function was highly correlated with the actual motor outcomes (r = 0.76; p0.05). These results demonstrate that the outcomes of a combined pharmacologic-DBS therapy can be predicted and may facilitate patient-specific treatment optimization for maximal benefits and minimal adverse effects.

BACKGROUND Microelectrode recording helps surgeons accurately localize boundaries of the subthalamic nucleus (STN) and surrounding structures in deep brain stimulation. OBJECTIVE To describe a novel adaptation of the Ben gun device to optimize efficient mapping. METHODS Patients who underwent STN deep brain stimulation over a 3-year period were reviewed. For the final year, the Ben gun was rotated 45° and the target was offset 1.4 mm lateral and anterior in the plane orthogonal to the intended trajectory to allow for simultaneous parallel tracks at target, 2.8 mm anterior (localizing the front of STN), and 2.8 mm lateral (identifying the internal capsule). Before this step, the initial pass consisted of 1 to 2 tracks with the frame center targeted to STN. The primary outcome measure was the number of passes required for accurate localization of the nucleus and boundaries. RESULTS Eighty-three electrodes were implanted in 45 patients (mean age, 62; range, 37-78 years), of which 29 electrodes were placed by the use of the new technique. One electrode (4%) required more than 1 pass using the new technique compared with 36 (67%) using the older technique (P < .01). The distance from original target to final electrode position increased from 0.67 ± 0.13 mm to 1.06 ± 0.15 mm (P < .05) with a greater tendency to move the final electrode position posteriorly. There was no statistically significant difference in benefit from neurostimulation. CONCLUSION This technique facilitates reliable localization of the STN with fewer passes, possibly decreasing the risks associated with more passes and longer duration of surgery.

Deep brain stimulation (DBS) is an established therapy for the management of advanced Parkinson’s disease (PD). However, the coupled adjustment of pharmacologic therapy and stimulation parameter settings is a time-consuming process and treatment outcomes are not always optimal. In this study, we develop a linear function that relates the DBS parameters, the levodopa dosage, and patient-specific preoperative clinical data with the actual treatment motor outcomes. To this end, we incorporate image-based patient-specific computer models of the volume of tissue activated by DBS in a multi-linear regression analysis (6 PD patients; 60 follow up visits). The resulting predictor function was highly correlated with the actual motor outcomes (r = 0.76; p

Sexually active male rats prefer a sexually receptive female to a nonreceptive female, and partner-preference tests provide one way of studying sexual motivation. Surgical deafferentation of the olfactory bulbs from all the known chemosensory systems of the nasal septum renders rats anosmic. In Experiment 1, we show that, although bulb deafferentation of male rats decreases some aspects of sexual performance, most deafferented males copulate and partner preference is not affected. In Experiment 2, we show that large excitotoxin lesions of the preoptic hypothalamus eliminate copulation, an effect that is correlated with damage to the anterior portions of the medial and lateral preoptic area. Lesions also decrease partner preference, an effect that is correlated (r = 0.82) with damage to a small part of the bed nucleus of the stria terminalis. Most males who do not copulate after hypothalamic lesions show a persistent, albeit reduced, preference for receptive females over nonreceptive females. This preference appears to depend on olfactory ability because bulb deafferentation of lesioned, noncopulating males virtually eliminates partner preference.

We describe a case of pseudobulbar crying associated with deep brain stimulation (DBS) in the region of the subthalamic nucleus (STN). Patients with pseudobulbar crying show no other evidence of subjective feelings of depression such as dysphoria, anhedonia, or vegetative signs. This may be accompanied by other symptoms of pseudobulbar palsy and has been reported to occur with ischaemic or structural lesions in both cortical and subcortical regions of the brain. Although depression has been observed to result from DBS in the region of the STN, pseudobulbar crying has not been reported. A single patient who reported the symptoms of pseudobulbar crying after placement of an STN DBS was tested in the off DBS and on DBS conditions. The patient was tested using all four DBS lead contacts and the observations and results of the examiners were recorded. The Geriatric Depression Scale was used to evaluate for depression in all of the conditions. The patient exhibited pseudobulbar crying when on monopolar stimulation at all four lead contacts. The pseudobulbar crying resolved off stimulation. This case describes another type of affective change that may be associated with stimulation in the region of or within the STN. Clinicians should be aware of this potential complication, the importance of differentiating it from stimulation induced depression, and its response to a serotonin reuptake inhibitor, such as sertraline.

Objective. When using an intracortical BCI (iBCI), users modulate their neural population activity to move an effector towards a target, stop accurately, and correct for movement errors. We call the rules that govern this modulation a 'feedback control policy'. A better understanding of these policies may inform the design of higher-performing neural decoders. Approach. We studied how three participants in the BrainGate2 pilot clinical trial used an iBCI to control a cursor in a 2D target acquisition task. Participants used a velocity decoder with exponential smoothing dynamics. Through offline analyses, we characterized the users' feedback control policies by modeling their neural activity as a function of cursor state and target position. We also tested whether users could adapt their policy to different decoder dynamics by varying the gain (speed scaling) and temporal smoothing parameters of the iBCI. Main results. We demonstrate that control policy assumptions made in previous studies do not fully describe the policies of our participants. To account for these discrepancies, we propose a new model that captures (1) how the user's neural population activity gradually declines as the cursor approaches the target from afar, then decreases more sharply as the cursor comes into contact with the target, (2) how the user makes constant feedback corrections even when the cursor is on top of the target, and (3) how the user actively accounts for the cursor's current velocity to avoid overshooting the target. Further, we show that users can adapt their control policy to decoder dynamics by attenuating neural modulation when the cursor gain is high and by damping the cursor velocity more strongly when the smoothing dynamics are high. Significance. Our control policy model may help to build better decoders, understand how neural activity varies during active iBCI control, and produce better simulations of closed-loop iBCI movements.

Gait and balance disturbances in Parkinson's disease (PD) can be debilitating and may lead to increased fall risk. Deep brain stimulation (DBS) is a treatment option once therapeutic benefits from medication are limited due to motor fluctuations and dyskinesia. Optimizing DBS parameters for gait and balance can be significantly more challenging than for other PD motor symptoms. Furthermore, inter-rater reliability of the standard clinical PD assessment scale, Unified Parkinson's Disease Rating Scale (UPDRS), may introduce bias and washout important features of gait and balance that may respond differently to PD therapies. Study objectives were to evaluate clinician UPDRS gait and balance scoring inter-rater reliability, UPDRS sensitivity to different aspects of gait and balance, and how kinematic features extracted from motion sensor data respond to stimulation. Forty-two subjects diagnosed with PD were recruited with varying degrees of gait and balance impairment. All subjects had been prescribed dopaminergic medication, and 20 subjects had previously undergone DBS surgery. Subjects performed seven items of the gait and balance subset of the UPDRS while wearing motion sensors on the sternum and each heel and thigh. Inter-rater reliability varied by UPDRS item. Correlation coefficients between at least one kinematic feature and corresponding UPDRS scores were greater than 0.75 for six of the seven items. Kinematic features improved (p0.05) from DBS-OFF to DBS-ON for three UPDRS items. Despite achieving high correlations with the UPDRS, evaluating individual kinematic features may help address inter-rater reliability issues and rater bias associated with focusing on different aspects of a motor task.

Depression has been estimated to affect 1 in 3 individuals with Parkinson's disease (PD) and can lead to worse health outcomes and decreased quality of life. Anxiety further complicates PD outcomes. Pharmacologic treatments of depression and anxiety can have negative side effects in patients with PD, including exacerbation of PD symptoms. There is a critical need for alternative treatment approaches that address depression and anxiety among patients with PD. Psychosocial or behavioral approaches are known to be effective for depression generally, but only a handful of studies have examined the role of psychosocial treatments of patients with depression in PD.The aim of this article was to review published psychosocial treatment studies of depression and anxiety in patients with PD.The PubMed database was searched for articles published in English before April 2011 using the terms Parkinson's disease, depression, anxiety, psychotherapy, cognitive therapy, behavioral treatment, behavioral therapy, nonpharmacologic treatment, psychoeducation, education, psychosocial treatment, and stress management. Articles included were prospective clinical trials utilizing specific depression or anxiety assessments as primary or secondary outcomes in patients with PD.Nine reports derived from 8 separate studies fit the inclusion criteria and were included in this review. All studies were published between 1997 and 2011, and all but 3 had small sample sizes (40 patients). Interventions included cognitive behavioral therapy (CBT), psychodrama, education, and behavior therapy as well as multidisciplinary rehabilitation. Cognitive behavioral therapy was the most studied and was shown to decrease depressive and anxiety symptoms in patients with PD. Other individual and group therapies may improve depression and anxiety in patients with PD, but the general paucity of studies and study methods limit the interpretation of these results.There have been few studies on psychosocial treatments that specifically assess change in depression and anxiety among patients with PD. While results for CBT and other modes of therapy are promising for acute management of depression and anxiety, longer term effects after treatment have been variable. There is a need for additional studies on psychosocial interventions in people with PD.

Hyperkinetic movement disorders are phenotypically linked by the presence of excess unwanted movements. In addition, they share common, neural pathways involved in voluntary motor control including primary and secondary motor and sensory cortices, the basal ganglia, thalamus, and cerebellum. The pathophysiology of these disorders appears to include similar alterations in physiological properties of neurons in these areas. Phenotypic differences in the hyperkinetic disorders, however, speak to the differing influence and degree of each of these changes and the various motor and, in some cases, non-motor pathways involved in mediating each disorder. In support of the commonality of neural pathways that underlie the development of different hyperkinetic disorders, surgical therapies may target common regions of the brain for the treatment of each of these disorders, and pharmacological therapies are aimed at receptors that regulate these same neural pathways. Much of our understanding of the physiological differences underlying hyperkinetic movement disorders has stemmed from comparisons to hypokinetic movement disorders as well as comparisons across the different hyperkinetic disorders. This chapter will detail (1) the anatomy of the basal ganglia and thalamocortical circuits and their role in the genesis of hyperkinetic disorders and (2) describe current knowledge of the neurophysiological changes that occur in each of these disorders. We will then present a general unified model of hyperkinetic movement disorders using hemiballism, dyskinesia, and dystonia as examples, outlining some of the differences that may occur in each. Tourette syndrome will be discussed separately since it would appear to have greater involvement of non-motor circuits. Finally, we will discuss myoclonus, a condition in which the anatomical areas involved are more diverse. While we often lose site of the role of non-motor and non-basal ganglia pathways in the development of these movement disorders, myoclonus serves as a reminder that many of these disorders have varying degrees of involvement of non-motor pathways and extra-basal ganglia pathology. As such, the presentation of each disorder and its response to the various treatment modalities may differ.

The objective was to develop and evaluate algorithms for quantifying gait and lower extremity bradykinesia in patients with Parkinson's disease using kinematic data recorded on a heel-worn motion sensor unit. Subjects were evaluated by three movement disorder neurologists on four domains taken from the Movement Disorders Society Unified Parkinson's Disease Rating Scale while wearing the motion sensor unit. Multiple linear regression models were developed based on the recorded kinematic data and clinician scores and produced outputs highly correlated to clinician scores with an average correlation coefficient of 0.86. The newly developed models have been integrated into a home-based system for monitoring Parkinson's disease motor symptoms.

This chapter reviews the anatomy, physiology, treatment and cognitive/neuropsychological aspects of movement disorders, of which Parkinson’s disease (PD) and parkinsonism are common manifestations. The neurologic, cognitive and behavioral aspects of movement disorders are covered in detail as are contemporary treatments and treatment outcomes. This chapter starts with an overview of the functional neuroanatomy of movement and discusses normal motor movement and disordered motor movement. We review the role of the basal ganglia and other anatomical areas implicated in movement disorders including Parkinson’s disease and parkinsonism and the role of dopamine and other neurotransmitters in disorders of movement. The next section reviews the clinical presentation of the movement disorders, inclusive of a description of each ­disorders cardinal symptoms and the differentiating characteristics among movement disorders. The cognitive and emotional symptoms associated with movement disorders are also discussed in detail. The later part of this chapter discusses the available treatment for movement disorders such as pharmacotherapy and surgical options and the motor and cognitive outcomes from such treatments. Next, the chapter provides a detailed analysis for the pre-surgical evaluation of patients being considered for surgical treatment, including a review of the pre- and post-operative neuropsychological assessment of patients with movement disorders. We discuss the changes in neuropsychological function that may be predicted post-surgically. Finally, we propose directions for future research in the course and treatment outcomes in motor, cognitive and behavioral symptoms associated with movement disorders.

Publisher Summary The understanding of the pathophysiology of the Parkinson's disease (PD), advances in surgical technique, and the development of imaging technology has led to the development of current surgical approaches for the treatment of this disease. This chapter reviews early empirical studies of surgical therapy and the evolution that has led to present neurosurgical approaches for the treatment of PD. These includes the effects of retrograde anatomical tracing studies in the hands of Hassler, implementation of the stereotaxis, advancements in neuroradiology from early ventriculography to CT and magnetic resonance imaging (MRI). Also important are the implementation of microelectrode physiology, the development of neurostimulator technologies, and now gene and transplant therapies. Advances in neuroscience have played a crucial role in the progress of this field, laying the groundwork for the understanding of the separate functions of the pyramidal and extrapyramidal motor systems, the role of dopaminergic neurons in PD.

Summary Since the early 1930s, physicians have developed and refined various surgical therapies for the treatment of Parkinson's disease. In this review we examine some of the problems associated with early surgical therapies, the development of new techniques and targets, and the results of clinical trials examining the safety and efficacy of these techniques. Ablative techniques include pallidotomy, thalamotomy, and, more recently, subthalamotomy. Because of concern over the high incidence of side-effects associated with bilateral ablative procedures, alternative approaches were explored. Deep brain stimulation (DBS) was subsequently developed and successfully applied in the internal globus pallidus, subthalamic nucleus, and thalamus for the treatment of Parkinson's disease. Recent approaches include biological neurorestorative techniques—surgical therapies with transplantation, gene therapy, and growth factors are all being studied. Although a great deal of work remains to be done, advances in surgical therapies for the treatment of Parkinson's disease are moving forward at an unprecedented pace.

Purpose: Functional MRI (fMRI) can provide insights into the functioning of the sensorimotor system, which is of particular interest in studying people with movement disorders or chronic pain conditions. This creates a demand for manipulanda that can fit and operate within the environment of a MRI scanner. Here, the authors present a magnetomechanical device that delivers a vibrotactile sensation to the skin with a force of approximately 9 N. Methods: MRI compatibility of the device was tested in a 3 T scanner using a phantom to simulate the head. Preliminary investigation into the effectiveness of the device at producing cortical and subcortical activity was also conducted with a group of seven healthy subjects. The vibration was applied to the right extensor carpi ulnaris tendon to induce a kinesthetic illusion of flexion and extension of the wrist. Results: The MRI compatibility tests showed the device did not produce image artifacts and the generated electromagnetic field did not disrupt the static magnetic field of the scanner or its operation. The subject group results showed activity in the contralateral putamen, premotor cortex, and dorsal lateral prefrontal cortex. Ipsilaterally, there was increased activity in the superior and inferior parietal lobules. Areas that activated bilaterally included the thalamus, anterior cingulate, secondary somatosensory areas (S2), temporal lobes, and visual association areas. Conclusions: This device offers an effective tool with precise control over the vibratory stimulus, delivering higher forces than some other types of devices (e.g., piezoelectric actuators). It can be useful for investigating sensory systems and sensorimotor integration.

Objective: Anti-NMDA receptor encephalitis is a paraneoplastic syndrome characterized by neuropsychiatric symptoms, involuntary movements, autonomic instability, and seizures. It is more common in young females and associated with a mature ovarian teratoma. We describe a classic presentation of a young female with mature ovarian teratoma, who had negative imaging on initial investigation for an ovarian neoplasm. Background A 25 year old female presented with seizure episode, headache, fever, and malaise. An extensive medical evaluation and review of her past medical and psychiatric histories were unremarkable. After admission she developed bizarre behaviors, hallucinations, and oral-facial dyskinesias, followed by dysautonomia resulting in transfer to ICU. Soon after, she was intubated for respiratory failure. Results: A lumbar puncture showed lymphocytic pleocytosis, with mildly elevated protein, and normal glucose. Due to concern for Anti-NMDAR encephalitis, a whole body CT and PET scan were obtained and reported unremarkable. Ultrasound and MRI pelvis revealed a “benign” right ovarian cyst. Gynecology was consulted; however, they felt an exploratory laparotomy was not warranted for a benign cyst. Six weeks following admission, Anti-NMDA receptor antibodies were reported positive. A repeat MRI pelvis, with fat saturation and in-out-of phase sequence, showed the right ovarian cyst consistent with a mature ovarian teratoma. She underwent bilateral salpingo-oophorectomy followed by five days of solumedrol, and cytoxan and rituximab a week later. Her mental state and involuntary movements continued to improve and was discharged to rehabilitation. Conclusions: Though, ultrasound is commonly used, MRI is more sensitive and specific for evaluation of adnexal masses. For ovarian teratomas, fat saturation along with in-and-out of phase sequence, should be included to detect the sebaceous content. If all imaging modalities continue to be negative, serial imaging is recommended. If clinical suspicion is high in a young female, exploratory laparoscopy or laparotomy should be considered for an ovarian teratoma. Disclosure: Dr. Ashraf has nothing to disclose. Dr. Janis has nothing to disclose. Dr. Walter has received personal compensation for activities with Deringer-Ney, Inc, Medtronic, Inc, Boehringer Ingelheim Pharmaceuticals and Teva Neuroscience as speaker, consultant and/or participant on an advisory board.

Autonomic dysfunction is common in parkinsonian syndromes, particularly those involving dysregulation of alpha-synuclein, and may result from neurodegeneration in autonomic regulatory regions of the brain or peripherial autonomic ganglia. The most limiting cardiovascular autonomic dysfunction in these diseases is orthostatic hypotension, which is particularly prominent in multiple system atrophy. Postprandial hypotension and supine hypertension, as well as dopaminergic therapy, often complicate the management of orthostatic hypotension in patients with parkinsonian syndromes.

Objective: To investigate whether a single daily dose of testosterone replacement gel has beneficial effects on testosterone deficiency symptoms, cognitive function, nonmotor symptoms of Parkinson disease (PD), and motor symptoms of PD. Background: Recently it has been observed that testosterone replacement therapy improves refractory nonmotor symptoms in testosterone-deficient men with PD. Many of the symptoms of testosterone deficiency are nonspecific and overlap with the nonmotor symptoms of PD, such as decreased enjoyment of life, lack of energy, sexual dysfunction, and depression. Replacement therapy for men with PD and comorbid testosterone deficiency may be an important addition to antiparkinsonian management strategies. Methods: A prospective open-labeled pilot study of testosterone topical gel (5 g of AndroGel; Unimed Pharmaceutical Inc, Deerfield, Ill) administered daily to testosterone-deficient (free testosterone80 pg/mL) men with PD. All 10 patients were followed up for 1 month and 6 patients were followed up for a total of 3 months. Patients were administered a battery of testosterone deficiency questionnaires, cognitive studies, and scales of PD nonmotor and motor function at baseline, 1, and 3 months. Results: With the daily transdermal testosterone gel, patients had an average increase in levels of free testosterone from baseline (53 pg/mL) to a 1-month follow-up visit (131 pg/mL; P=.06) and to a 3-month follow-up visit (98 pg/mL; P=.04). Testosterone deficiency symptoms improved in these patients (St Louis Testosterone Deficiency Questionnaire) from baseline (7.9 deficiency symptoms) to 1 month (5.6 deficiency symptoms, P=.04) and 3 months (5.8 deficiency symptoms, P=.08). The Unified Parkinson’s Disease Rating Scale IV showed improvement at 1 month (P=.008). Additionally, there were trends toward improvement in the following scales: Unified Parkinson’s Disease Rating Scale I at the 3-month follow-up (P = .09), Letter Fluency at the 3-month follow-up (P=.08), and the Hamilton Anxiety Scale at the 1-month follow-up (P=.09). Conclusions: A daily dose of transdermal testosterone gel improved testosterone deficiency symptoms in men with PD. Although there were trends in improvement in other nonmotor and motor symptoms of PD, future placebo control studies will need to be powered to answer these important questions. Whether testosterone deficiency is simply a comorbidity in PD or whether it plays a role in the pathogenesis of disease also remains for future study. Arch Neurol. 2002;59:1750-1753

Shadowgraphy was employed to study snow saltation in boundary-layer wind tunnel experiments with fresh, naturally deposited snow. The shadowgraphy method allowed for a temporally and spatially high-resolution investigation of snow particle characteristics within a measurement area of up to 50 mm × 50 mm. Snow particle size and number characteristics, and their variation with height in the saltation layer, were analysed. The following observations and findings were made for the saltation layer: (1) the particle number decreases exponentially with height, (2) the mean particle diameter is fairly constant, with a very slight tendency to decrease with height, (3) the maximum particle diameter decreases linearly with height, and (4) the snow particle size distribution can be adequately described by gamma probability density functions. The shape and scale parameters of the gamma distribution were found to vary systematically, though only slightly, with height over ground and between experiments with different snowpack characteristics.