Differential Modulation of Local Field Potentials in the Primary and Premotor Cortices during Ipsilateral and Contralateral Reach to Grasp in Macaque Monkeys.

Hand movements are associated with modulations of neuronal activity across several interconnected cortical areas, including the primary motor cortex (M1) and the dorsal and ventral premotor cortices (PMd and PMv). Local field potentials (LFPs) provide a link between neuronal discharges and synaptic inputs. Our current understanding of how LFPs vary in M1, PMd, and PMv during contralateral and ipsilateral movements is incomplete. To help reveal unique features in the pattern of modulations, we simultaneously recorded LFPs in these areas in two macaque monkeys performing reach and grasp movements with either the right or left hand. The greatest effector-dependent differences were seen in M1, at low (≤13 Hz) and γ frequencies. In premotor areas, differences related to hand use were only present in low frequencies. PMv exhibited the greatest increase in low frequencies during instruction cues and the smallest effector-dependent modulation during movement execution. In PMd, δ oscillations were greater during contralateral reach and grasp, and ß activity increased during contralateral grasp. In contrast, ß oscillations decreased in M1 and PMv. These results suggest that while M1 primarily exhibits effector-specific LFP activity, premotor areas compute more effector-independent aspects of the task requirements, particularly during movement preparation for PMv and production for PMd. The generation of precise hand movements likely relies on the combination of complementary information contained in the unique pattern of neural modulations contained in each cortical area. Accordingly, integrating LFPs from premotor areas and M1 could enhance the performance and robustness of brain-machine interfaces.

Multi-muscle synergies in preparation for gait initiation in Parkinson's disease.

OBJECTIVE: We investigated changes in indices of muscle synergies prior to gait initiation and the effects of gaze shift in patients with Parkinson's disease (PD). A long-term objective of the study is to develop a method for quantitative assessment of gait-initiation problems in PD. METHODS: PD patients without clinical signs of postural instability and two control groups (age-matched and young) performed a gait initiation task in a self-paced manner, with and without a quick prior gaze shift produced by turning the head. Muscle groups with parallel scaling of activation levels (muscle modes) were identified as factors in the muscle activation space. Synergy index stabilizing center of pressure trajectory in the anterior-posterior and medio-lateral directions (indices of stability) was quantified in the muscle mode space. A drop in the synergy index in preparation to gait initiation (anticipatory synergy adjustment, ASA) was quantified. RESULTS: Compared to the control groups, PD patients showed significantly smaller synergy indices and ASA for both directions of the center of pressure shift. Both PD and age-matched controls, but not younger controls, showed detrimental effects of the prior gaze shift on the ASA indices. CONCLUSIONS: PD patients without clinically significant posture or gait disorders show impaired stability of the center of pressure and its diminished adjustment during gait initiation. SIGNIFICANCE: The indices of stability and ASA may be useful to monitor pre-clinical gait disorders, and lower ASA may be relevant to emergence of freezing of gait in PD.

A machine learning approach to characterize sequential movement-related states in premotor and motor cortices.

Nonhuman primate (NHP) movement kinematics have been decoded from spikes and local field potentials (LFPs) recorded during motor tasks. However, the potential of LFPs to provide network-like characterizations of neural dynamics during planning and execution of sequential movements requires further exploration. Is the aggregate nature of LFPs suitable to construct informative brain state descriptors of movement preparation and execution? To investigate this, we developed a framework to process LFPs based on machine-learning classifiers and analyzed LFP from a primate, implanted with several microelectrode arrays covering the premotor cortex in both hemispheres and the primary motor cortex on one side. The monkey performed a reach-to-grasp task, consisting of five consecutive states, starting from rest until a rewarding target (food) was attained. We use this five-state task to characterize neural activity within eight frequency bands, using spectral amplitude and pairwise correlations across electrodes as features. Our results show that we could best distinguish all five movement-related states using the highest frequency band (200-500 Hz), yielding an 87% accuracy with spectral amplitude, and 60% with pairwise electrode correlation. Further analyses characterized each movement-related state, showing differential neuronal population activity at above-γ frequencies during the various stages of movement. Furthermore, the topological distribution for the high-frequency LFPs allowed for a highly significant set of pairwise correlations, strongly suggesting a concerted distribution of movement planning and execution function is distributed across premotor and primary motor cortices in a specific fashion, and is most significant in the low ripple (100-150 Hz), high ripple (150-200 Hz), and multiunit frequency bands. In summary, our results show that the concerted use of novel machine-learning techniques with coarse grained queue broad signals such as LFPs may be successfully used to track and decode fine movement aspects involving preparation, reach, grasp, and reward retrieval across several brain regions.NEW & NOTEWORTHY Local field potentials (LFPs), despite lower spatial resolution compared to single-neuron recordings, can be used with machine learning classifiers to decode sequential movements involving motor preparation, execution, and reward retrieval. Our results revealed heterogeneity of neural activity on small spatial scales, further evidencing the utility of micro-electrode array recordings for complex movement decoding. With further advancement, high-dimensional LFPs may become the gold standard for brain-computer interfaces such as neural prostheses in the near future.

Biomechanics of Vertical Posture and Control with Referent Joint Configurations.

Our study compared the results of two methods of analysis of postural sway during human quiet standing, the rambling-trembling (Rm-Tr) decomposition and the analysis of the point of intersection of the ground reaction forces (zIP analysis). Young, healthy subjects were required to stand naturally and with an increased level of leg/trunk muscle co-activation under visual feedback on the magnitude of a combined index of muscle activation (muscle mode). The main findings included the shift of zIP toward higher frequencies and strong correlations between Tr and zIP when the subjects stood with increased muscle co-activation. We interpret the results within the idea of whole-body control with a set of primitives associated with referent coordinates in the joint configuration space.

Synergic control of action in levodopa-naïve Parkinson's disease patients: II. Multi-muscle synergies stabilizing vertical posture.

Postural instability is a major disabling feature in Parkinson's disease (PD). We quantified the organization of leg and trunk muscles into synergies stabilizing the center of pressure (COP) coordinate within the uncontrolled manifold hypothesis in levodopa-naïve patients with PD and age-matched control subjects. The main hypothesis was that changes in the synergic control of posture are present early in the PD process even before levodopa exposure. Eleven levodopa-naïve patients with PD and 11 healthy controls performed whole-body cyclical voluntary sway tasks and a self-initiated load-release task during standing on a force plate. Surface electromyographic activity in 13 muscles on the right side of the body was analyzed to identify muscle groups with parallel scaling of activation levels (M-modes). Data were collected both before ("off-drug") and approximately 60 min after the first dose of 25/100 carbidopa/levodopa ("on-drug"). COP-stabilizing synergies were quantified for the load-release task. Levodopa-naïve patients with PD showed no COP-stabilizing synergy "off-drug", whereas controls showed posture-stabilizing multi-M-mode synergy. "On-drug", patients with PD demonstrated a significant increase in the synergy index. There were no significant drug effects on the M-mode composition, anticipatory postural adjustments, indices of motor equivalence, or indices of COP variability. The results suggest that levodopa-naïve patients with PD already show impaired posture-stabilizing multi-muscle synergies that may be used as promising behavioral biomarkers for emerging postural disorders in PD. Moreover, levodopa modified synergy metrics differently in these levodopa-naïve patients compared to a previous study of patients on chronic antiparkinsonian medications (Falaki et al. in J Electromyogr Kinesiol 33:20-26, 2017a), suggesting different neurocircuitry involvement.

Case Studies in Neuroscience: The central and somatosensory contributions to finger interdependence and coordination: lessons from a study of a "deafferented person".

We tested finger force interdependence and multifinger force-stabilizing synergies in a patient with large-fiber peripheral neuropathy ("deafferented person"). The subject performed a range of tasks involving accurate force production with one finger and with four fingers. In one-finger tasks, nontask fingers showed unintentional force production (enslaving) with an atypical pattern: very large indices for the lateral (index and little) fingers and relatively small indices for the central (middle and ring) fingers. Indices of multifinger synergies stabilizing total force and of anticipatory synergy adjustments in preparation to quick force pulses were similar to those in age-matched control females. During constant force production, removing visual feedback led to a slow force drift to lower values (by ~25% over 15 s). The results support the idea of a neural origin of enslaving and suggest that the patterns observed in the deafferented person were reorganized based on everyday manipulation tasks. The lack of significant changes in the synergy index shows that synergic control can be organized in the absence of somatosensory feedback. We discuss the control of the hand in deafferented persons within the α-model of the equilibrium-point hypothesis and suggest that force drift results from an unintentional drift of the control variables to muscles toward zero values. NEW & NOTEWORTHY We demonstrate atypical patterns of finger enslaving and unchanged force-stabilizing synergies in a person with large-fiber peripheral neuropathy. The results speak strongly in favor of central origin of enslaving and its reorganization based on everyday manipulation tasks. The data show that synergic control can be implemented in the absence of somatosensory feedback. We discuss the control of the hand in deafferented persons within the α-model of the equilibrium-point hypothesis.

Preparation to a quick whole-body action: control with referent body orientation and multi-muscle synergies.

We examined the control of postural stability in preparation to a discrete, quick whole-body sway toward a target and back to the initial position. Several predictions were tested based on the theory of control with referent body orientation and the notion of multi-muscle synergies stabilizing center of pressure (COP) coordinate. Healthy, young adults performed fast, discrete whole-body motion forward-and-back and backward-and-back under visual feedback on the COP. We used two methods to assess COP stability, analysis of inter-trial variance and analysis of motor equivalence in the muscle activation space. Actions were always preceded by COP counter-movements. Backward COP shifts were faster, and the indices of multi-muscle synergies stabilizing COP were higher prior to those actions. Patterns of muscle activation at the motion onset supported the idea of a gradual shift in the referent body orientation. Prior to the backward movements, there was a trend toward higher muscle co-activation, compared to reciprocal activation. We found strong correlations between the sets of indices of motor equivalence and those of inter-trial variance. Overall, the results support the theory of control with referent coordinates and the idea of multi-muscle synergies stabilizing posture by confirming a number of non-trivial predictions based on these concepts. The findings favor using indices of motor equivalence in clinical studies to minimize the number of trials performed by each subject.

Effects of Voluntary Agonist-Antagonist Coactivation on Stability of Vertical Posture.

We explored the effects of voluntary coactivation of agonist-antagonist leg and trunk muscles on stability of vertical posture. Young healthy subjects performed several tasks while standing with no additional muscle coactivation, low coactivation, and high coactivation. Postural stability was estimated using indices of postural sway and of intertrial variance in the space of muscle groups with parallel scaling of activation levels (M-modes). An increase in coactivation led to a significant increase in the postural sway speed reflected in faster rambling and trembling trajectories. Coactivation also led to a relative drop in the variance component that had no effects on the center of pressure coordinate and an increase in the component that shifted the center of pressure. We conclude that additional muscle coactivation does not help to stabilize vertical posture and is more likely to lead to postural destabilization. The results are consistent with an earlier hypothesis on muscle coactivation ensuring abundance (excessive degrees of freedom) at the level of control variables.

Stability of vertical posture explored with unexpected mechanical perturbations: synergy indices and motor equivalence.

We explored the relations between indices of mechanical stability of vertical posture and synergy indices under unexpected perturbations. The main hypotheses predicted higher posture-stabilizing synergy indices and higher mechanical indices of center of pressure stability during perturbations perceived by subjects as less challenging. Healthy subjects stood on a force platform and held in fully extended arms a bar attached to two loads acting downward and upward. One of the loads was unexpectedly released by the experimenter causing a postural perturbations. In different series, subjects either knew or did not know which of the two loads would be released. Forward perturbations were perceived as more challenging and accompanied by co-activation patterns among the main agonist-antagonist pairs. Backward perturbation led to reciprocal muscle activation patterns and was accompanied by indices of mechanical stability and of posture-stabilizing synergy which indicated higher stability. Changes in synergy indices were observed as early as 50-100 ms following the perturbation reflecting involuntary mechanisms. In contrast, predictability of perturbation direction had weak or no effect on mechanical and synergy indices of stability. These observations are interpreted within a hierarchical scheme of synergic control of motor tasks and a hypothesis on the control of movements with shifts of referent coordinates. The findings show direct correspondence between stability indices based on mechanics and on the analysis of multi-muscle synergies. They suggest that involuntary posture-stabilizing mechanisms show synergic organization. They also show that predictability of perturbation direction has strong effects on anticipatory postural adjustment but not corrective adjustments. We offer an interpretation of co-activation patterns that questions their contribution to postural stability.

Systemic effects of deep brain stimulation on synergic control in Parkinson's disease.

OBJECTIVE: We explored effects of deep brain stimulation (DBS) in patients with Parkinson's disease (PD) on the synergic control of fingers in a multi-finger force production task and of muscles in a task involving vertical posture. METHODS: The finger task involved the four fingers of a hand producing accurate total force followed by a targeted quick force pulse. The postural task involved releasing a load from extended arms. The analysis of synergies was performed within the framework of the uncontrolled manifold hypothesis. RESULTS: DBS led to no significant changes in indices of stability during steady-state phases. In contrast, DBS improved indices of agility, quantified as anticipatory synergy adjustments that reduced stability of salient performance variables in preparation to their quick change. There were moderate-to-strong correlations between indices of both stability and agility measured in the multi-finger force production and multi-muscle whole-body action. CONCLUSIONS: Our results point at systemic changes in synergic control in PD. They show that DBS is effective in improving only one components of synergic control related to agility in performance being relatively ineffective for the stability component. SIGNIFICANCE: The results show systemic brain mechanisms of synergies and suggest differential effects of DBS on indices of stability and agility.

Synergies and Motor Equivalence in Voluntary Sway Tasks: The Effects of Visual and Mechanical Constraints.

The authors used two analyses developed within the framework of the uncontrolled manifold hypothesis to quantify multimuscle synergies during voluntary body sway: analysis of intertrial variance and analysis of motor equivalence with respect to the center of pressure (COP) trajectory. Participants performed voluntary sway tasks in the anteroposterior direction at 0.33 and 0.66 Hz. Muscle groups were identified in the space of muscle activations and used as elemental variables in the synergy analyses. Changing mechanical and vision feedback-based constraints led to significant changes in indices of sway performance such as COP deviations in the uninstructed, mediolateral direction and indices of spontaneous postural sway. In contrast, there were no significant effects on synergy indices. These findings show that the neural control of performance and of its stability may involve different control variables and neurophysiological structures. There were strong correlations between the indices of motor equivalence and those computed using the intercycle variance analysis. This result is potentially important for studies of patients with movement disorders who may be unable to perform multiple trials (cycles) at any given task, making analysis of motor equivalence of single trials a viable alternative to explore changes in stability of actions.

Unintentional drifts during quiet stance and voluntary body sway.

We explored unintentional drifts in voluntary whole-body sway tasks following the removal of visual feedback. The main hypothesis was that the unintentional drifts were produced by drifts of referent coordinates for salient performance variables. Young healthy subjects stood quietly on a force platform and also performed voluntary body sway at 0.5 Hz both in the anterio-posterior and medio-lateral directions. Visual feedback on the center of pressure (COP) coordinate was provided and then turned off. During quiet stance trials, the subjects matched the initial COP coordinate with a target shifted by 3 cm anterior, posterior, left, or right from the coordinate during natural standing and activated the right tibialis anterior to 30% of its maximal voluntary contraction. During cyclical voluntary sway task, the nominal sway amplitude was always 4 cm while the midpoint was at one of the four mentioned locations. Removing visual feedback caused COP drifts during quiet stance trials that were consistent across trials performed by a subject but could be in opposite directions across subjects; there was a consistent drop in the activation level of tibialis anterior. During voluntary body sway, removing visual feedback caused a consistent increase in the voluntary sway amplitude and a drift of the midpoint that was consistent within but not across subjects. Motor equivalent and non-motor equivalent inter-cycle motion components were quantified within the space of muscle groups (muscle modes) under visual feedback and at the end of the period without visual feedback. Throughout the trial, there were large motor equivalent motion components, and they increased over the period without visual feedback. The results corroborate the idea that referent coordinate drifts at different levels of the control hierarchy can lead to unintentional drifts in performance. It suggests that directions of COP drifts are defined by two main factors, drift of the body referent coordinate toward the actual coordinate (that can lead to fall) and an opposite drift to ensure body motion to a safer location. Analysis of motor equivalence suggests that postural stability is not compromised during unintentional drifts in performance in contrast to earlier studies of multi-finger tasks. This may be due to the vital importance of postural stability for everyday actions.

Motor equivalence and structure of variance: multi-muscle postural synergies in Parkinson's disease.

We explored posture-stabilizing multi-muscle synergies with two methods of analysis of multi-element, abundant systems: (1) Analysis of inter-cycle variance; and (2) Analysis of motor equivalence, both quantified within the framework of the uncontrolled manifold (UCM) hypothesis. Data collected in two earlier studies of patients with Parkinson's disease (PD) were re-analyzed. One study compared synergies in the space of muscle modes (muscle groups with parallel scaling of activation) during tasks performed by early-stage PD patients and controls. The other study explored the effects of dopaminergic medication on multi-muscle-mode synergies. Inter-cycle variance and absolute magnitude of the center of pressure displacement across consecutive cycles were quantified during voluntary whole-body sway within the UCM and orthogonal to the UCM space. The patients showed smaller indices of variance within the UCM and motor equivalence compared to controls. The indices were also smaller in the off-drug compared to on-drug condition. There were strong across-subject correlations between the inter-cycle variance within/orthogonal to the UCM and motor equivalent/non-motor equivalent displacements. This study has shown that, at least for cyclical tasks, analysis of variance and analysis of motor equivalence lead to metrics of stability that correlate with each other and show similar effects of disease and medication. These results show, for the first time, intimate links between indices of variance and motor equivalence. They suggest that analysis of motor equivalence, which requires only a handful of trials, could be used broadly in the field of motor disorders to analyze problems with action stability.

Dopaminergic modulation of multi-muscle synergies in postural tasks performed by patients with Parkinson's disease.

BACKGROUND: Postural instability is one of most disabling motor symptoms in Parkinson's disease. Indices of multi-muscle synergies are new measurements of postural stability. OBJECTIVES: We explored the effects of dopamine-replacement drugs on multi-muscle synergies stabilizing center of pressure coordinate and their adjustments prior to a self-triggered perturbation in patients with Parkinson's disease. We hypothesized that both synergy indices and synergy adjustments would be improved on dopaminergic drugs. METHODS: Patients at Hoehn-Yahr stages II and III performed whole-body tasks both off- and on-drugs while standing. Muscle modes were identified as factors in the muscle activation space. Synergy indices stabilizing center of pressure in the anterior-posterior direction were quantified in the muscle mode space during a load-release task. RESULTS: Dopamine-replacement drugs led to more consistent organization of muscles in stable groups (muscle modes). On-drugs patients showed larger indices of synergies and anticipatory synergy adjustments. In contrast, no medication effects were seen on anticipatory postural adjustments or other performance indices. CONCLUSIONS: Dopamine-replacement drugs lead to significant changes in characteristics of multi-muscle synergies in Parkinson's disease. Studies of synergies may provide a biomarker sensitive to problems with postural stability and agility and to efficacy of dopamine-replacement therapy.

Anticipatory postural adjustments and anticipatory synergy adjustments: preparing to a postural perturbation with predictable and unpredictable direction.

We explored two aspects of feed-forward postural control, anticipatory postural adjustments (APAs) and anticipatory synergy adjustments (ASAs) seen prior to self-triggered unloading with known and unknown direction of the perturbation. In particular, we tested two main hypotheses predicting contrasting changes in APAs and ASAs. The first hypothesis predicted no major changes in ASAs. The second hypothesis predicted delayed APAs with predominance of co-contraction patterns when perturbation direction was unknown. Healthy subjects stood on the force plate and held a bar with two loads acting in the forward and backward directions. They pressed a trigger that released one of the loads causing a postural perturbation. In different series, the direction of the perturbation was either known (the same load released in all trials) or unknown (the subjects did not know which of the two loads would be released). Surface electromyograms were recorded and used to quantify APAs, synergies stabilizing center of pressure coordinate (within the uncontrolled manifold hypothesis), and ASA. APAs and ASAs were seen in all conditions. APAs were delayed, and predominance of co-contraction patterns was seen under the conditions with unpredictable direction of perturbation. In contrast, no significant changes in synergies and ASAs were seen. Overall, these results show that feed-forward control of vertical posture has two distinct components, reflected in APAs and ASAs, which show qualitatively different adjustments with changes in predictability of the direction of perturbation. These results are interpreted within the recently proposed hierarchical scheme of the synergic control of motor tasks. The observations underscore the complexity of the feed-forward postural control, which involves separate changes in salient performance variables (such as coordinate of the center of pressure) and in their stability properties.

Impaired synergic control of posture in Parkinson's patients without postural instability.

BACKGROUND: Postural instability is one of most disabling motor symptoms in Parkinson's disease. Indices of multi-muscle synergies are new measurements of movement and postural stability. OBJECTIVES: Multi-muscle synergies stabilizing vertical posture were studied in Parkinson's disease patients without clinical symptoms of postural instability (Hoehn-Yahr ≤ II) and age-matched controls. We tested the hypothesis that both synergy indices during quiet standing and synergy adjustments to self-triggered postural perturbations would be reduced in patients. METHODS: Eleven Parkinson's disease patients and 11 controls performed whole-body tasks while standing. Surface electromyography was used to quantify synergy indices stabilizing center of pressure shifts in the anterior-posterior direction during a load-release task. RESULTS: Parkinson's disease patients showed a significantly lower percentage of variance in the muscle activation space accounted for by the first four principal components, significantly reduced synergy indices during steady state, and significantly reduced anticipatory synergy adjustments (a drop in the synergy index prior to the self-triggered unloading). CONCLUSIONS: The study demonstrates for the first time that impaired synergic control in Parkinson's disease can be quantified in postural tasks, even in patients without clinical manifestations of postural instability. Synergy measurements may provide a biomarker sensitive for early problems with postural stability in Parkinson's disease.

Unintentional movements induced by sequential transient perturbations in a multi-joint positional task.

We explored the phenomenon of unintentional movements of a multi-joint effector produced by multiple transient changes in the external force. The subjects performed a position-holding task against a constant bias force produced by a robot and were instructed not to intervene voluntarily with arm movements produced by changes in the robot force. The robot produced a smooth force increase leading to hand movement from the trunk, followed by a dwell time. Then, the force dropped to its initial value leading to hand movement toward the initial position but with an undershot. Such perturbation episodes were repeated four times in a row. The accumulated perturbation and undershoot distances kept increasing without saturation within the sequence of four perturbation episode. The limb apparent stiffness before dwell time increased over sequential perturbations while apparent stiffness after dwell time decreased. We interpret the results as consequences of a drift of the hand referent coordinate (RC) caused by a hypothesized RC-back-coupling mechanism and a coupled drift of the apparent stiffness. The results show that RC-back-coupling continues to lead to unintentional movements over repeated perturbations and is accompanied by a relatively slow re-setting process.

Task-specific stability in muscle activation space during unintentional movements.

We used robot-generated perturbations applied during position-holding tasks to explore stability of induced unintentional movements in a multidimensional space of muscle activations. Healthy subjects held the handle of a robot against a constant bias force and were instructed not to interfere with hand movements produced by changes in the external force. Transient force changes were applied leading to handle displacement away from the initial position and then back toward the initial position. Intertrial variance in the space of muscle modes (eigenvectors in the muscle activations space) was quantified within two subspaces, corresponding to unchanged handle coordinate and to changes in the handle coordinate. Most variance was confined to the former subspace in each of the three phases of movement, the initial steady state, the intermediate position, and the final steady state. The same result was found when the changes in muscle activation were analyzed between the initial and final steady states. Changes in the dwell time between the perturbation force application and removal led to different final hand locations undershooting the initial position. The magnitude of the undershot scaled with the dwell time, while the structure of variance in the muscle activation space did not depend on the dwell time. We conclude that stability of the hand coordinate is ensured during both intentional and unintentional actions via similar mechanisms. Relative equifinality in the external space after transient perturbations may be associated with varying states in the redundant space of muscle activations. The results fit a hierarchical scheme for the control of voluntary movements with referent configurations and redundant mapping between the levels of the hierarchy.

Clinical and histopathological analysis of oral Squamouscell carcinoma of young patients in Mashhad, Iran: A retrospective study and review of literatures

Objectives: Oral Squamous cell carcinoma (OSCC) is primarily a disease that mainly occurs in males in their sixthand seventh decades of life and is rare in young adults.Study Design: In this retrospective study, records of patients under the age of 40, with the diagnosis of OSCC inthe Oral Medicine Department of Mashhad Dental Faculty during the past 13 years were analyzed. Their socioeconomicdata, demographic, clinical and histopathological characteristics, risk factors, familial history were assessedand applicable studies and case reports in the literatures were reviewed. PCR (Polymerase chain reaction)analysis was also done for detection of human papilloma virus (HPV).Results: From 158 cases of OSCC diagnosed in our centre, 21 patients were younger than 40 years. Most of themwere young men (12 cases). There was no significant risk factor in this group. The most common site of involvementwas the tongue. The most common clinical presentation was exophytic lesion with ulcer. No HPV DNA wasdetected in these patients.Conclusion: Characteristics of OSCC in young patients are different from older age group. Major risk factors (smokingand alcohol consumption and HPV) were not etiologic factors for OSCC in young patients in our province (AU)