Model-based and model-free mechanisms in methamphetamine use disorder

People with methamphetamine use disorder (MUD) struggle to shift their behaviour from methamphetamine-orientated habits to goal-oriented choices. The model-based/model-free framework is well suited to understand this difficulty by unpacking the computational mechanisms that support experienced-based (model-free) and goal-directed (model-based) choices. We aimed to examine whether 1) participants with MUD differed from controls on behavioural proxies and/or computational mechanisms of model-based/model-free choices; 2) model-based/model-free decision-making correlated with MUD symptoms; and 3) model-based/model-free deficits improved over six weeks in the group with MUD. Participants with MUD and controls with similar age, IQ and socioeconomic status completed the Two-Step Task at treatment commencement (MUD n = 30, Controls n = 31) and six weeks later (MUD n = 23, Controls n = 26). We examined behavioural proxies of model-based/model-free decisions using mixed logistic regression, and their underlying mechanisms using computational modelling. At a behavioural level, participants with MUD were more likely to switch their choices following rewarded actions, although this pattern improved at follow up. At a computational level, groups were similar in their use of model-based mechanisms, but participants with MUD were less likely to apply model-free mechanisms and less likely to repeat rewarded actions. We did not find evidence that individual differences in model-based or model-free parameters were associated with greater severity of methamphetamine dependence, nor did we find that group differences in computational parameters changed between baseline and follow-up assessment. Decision-making challenges in people with MUD are likely related to difficulties in pursuing choices previously associated with positive outcomes.

Proof-of-concept trial of Goal Management Training+ to improve executive functions and treatment outcomes in methamphetamine use disorder

BACKGROUND

Deficits in executive function are common in methamphetamine use disorder (MUD), likely contributing to difficulties in sustained treatment success. Cognitive remediation interventions are designed to treat such deficits but have not been adapted to the needs of people with MUD. This study presents a proof-of-concept trial to evaluate a new cognitive remediation program for MUD, Goal Management Training⁺ (GMT⁺).

METHODS

This was a cluster-randomised crossover trial comparing GMT⁺ with a psychoeducation-based control (Brain Health Workshop; BHW). GMT⁺ is a therapist-administered group-based cognitive remediation for executive dysfunction comprising four 90-minute weekly sessions and daily journal activities. BHW is a lifestyle psychoeducation program matched to GMT⁺ for therapist involvement, format, and duration. Participants (n = 36; GMT n = 17; BHW n = 19) were recruited from therapeutic communities in Victoria, Australia. Primary outcomes included intervention acceptability, feasibility, and improvements in self-reported executive function. Secondary outcomes included cognitive tests of executive function, severity of methamphetamine dependence, craving, and quality of life. We performed mixed linear modelling and calculated Hedges' g effect sizes.

RESULTS

GMT⁺ participant ratings and program retention indicated high acceptability. There was no difference between GMT⁺ and BHW on self-reported executive function (g = 0.06). Cognitive tasks suggested benefits of GMT⁺ on information gathering (g = 0.88) and delay-discounting (g = 0.80). Severity of methamphetamine dependence decreased more in GMT⁺ (g = 1.47).

CONCLUSIONS

GMT⁺ was well-accepted but did not improve self-reported executive functioning. Secondary outcomes suggested GMT⁺ was beneficial for objective cognitive performance and severity of dependence.

Computational models of exploration and exploitation characterise onset and efficacy of treatment in methamphetamine use disorder

People with Methamphetamine Use Disorder (PwMUD) spend substantial time and resources on substance use, which hinders their ability to explore alternate reinforcers. Gold‐standard behavioural treatments attempt to remedy this by encouraging action towards non‐drug reinforcers, but substance use often persists. We aimed to unravel the mechanistic drivers of this behaviour by applying a computational model of explore/exploit behaviour to decision‐making data (Iowa Gambling Task) from 106 PwMUD and 48 controls. We then examined the longitudinal link between explore/exploit mechanisms and changes in methamphetamine use 6 weeks later. Exploitation parameters included reinforcement sensitivity and inverse decay (i.e., number of past outcomes used to guide choices). Exploration parameters included maximum directed exploration value (i.e., value of trying novel actions). The Timeline Follow Back measured changes in methamphetamine use. Compared to controls, PwMUD showed deficits in exploitative decision‐making, characterised by reduced reinforcement sensitivity, U = 3065, p = 0.009, and less use of previous choice outcomes, U = 3062, p = 0.010. This was accompanied by a behavioural pattern of frequent shifting between choices, which appeared consistent with random exploration. Furthermore, PwMUD with greater reductions of methamphetamine use at 6 weeks had increased directed exploration (β = 0.22, p = 0.045); greater use of past choice outcomes (β = −0.39, p = 0.002) and greater choice consistency (β = −0.39, p = 0.002). Therefore, limited computational exploitation and increased behavioural exploration characterise PwMUD's presentation to treatment, while increased directed exploration, use of past choice outcomes and choice consistency predict greater reductions of methamphetamine use.

Development of Goal Management Training+ for Methamphetamine Use Disorder Through Collaborative Design

BACKGROUND

Methamphetamine use disorder (MUD) is associated with executive dysfunctions, which are linked with poorer treatment outcomes including earlier drop out and relapse. However, current treatments for MUD do not address executive functions. Goal Management Training (GMT) is an evidence-based cognitive remediation program for executive dysfunction, although required modifications to enhance its relevance and application within addiction treatment settings. This study aimed to (1) tailor GMT to the key cognitive deficits and typical treatment duration of MUD; (2) explore consumers' (people with MUD) engagement with the revised program; (3) implement a prototype of the program with consumers; and (4) present the manualized standard administration to clinical service providers.

METHODS

We followed the Medical Research Council Complex Interventions Framework and employed an evidence- and person-based intervention development process. We used a four-phased approach and collaborated with neuropsychology experts, design researchers in healthcare, consumers with MUD, and clinical service providers. Each aim was addressed in a separate study phase; including content refinement and review with neuropsychology experts (phase 1), intervention design and collaboration with consumers (phase 2), prototype development and review with consumers (phase 3), and final program modifications and review with clinical stakeholders (phase 4).

RESULTS

Findings from phase 1 indicated support for targeting four cognitive processes (attention, impulse control, goal setting, and decision-making). Key feedback included the need to help habitualize cognitive strategies and to guide consumers in applying these strategies in emotionally salient situations. Findings from phases 2 and 3 indicated consumer support for the program strategies and materials but highlighted the need to further enhance the personal relevance of specific content and journal activities. Findings from phase 4 provided clinicians support for the revised program but indicated an opportunity to minimize unintended effects. We present the intervention materials for the final revised program, Goal Management Training⁺ (GMT⁺), in line with TIDieR guidelines.

CONCLUSIONS

GMT⁺ targets key cognitive processes and is sensitive to the clinical needs of people with MUD. Our intervention development process was important for informing the active ingredients and materials for GMT⁺, and indicated initial consumer and provider acceptability prior to conducting a clinical trial.

Cognitive boosting interventions for impulsivity in addiction: a systematic review and meta-analysis of cognitive training, remediation and pharmacological enhancement

AIMS

To evaluate and compare the effects of three cognitive boosting intervention approaches (computerised cognitive training, cognitive remediation and pharmacological cognitive enhancers) on measures of impulsive action and impulsive choice.

DESIGN

Systematic review and meta-analysis of publications that reported original controlled trials of cognitive boosting interventions.

SETTING

Studies conducted anywhere in the world. No language restrictions were applied.

PARTICIPANTS

Treatment-seeking adults with substance use disorder or gambling disorder.

MEASUREMENTS

Our primary outcome was a reduction in impulsive action or choice on a validated cognitive measure post-intervention. We assessed risk of bias using the Cochrane Collaboration tool and determined pooled estimates from published reports. We performed random-effects analyses for impulsive action and impulsive choice outcomes and planned moderator analyses.

FINDINGS

Of 2204 unique studies identified, 60 were included in the full-text review. Twenty-three articles were considered eligible for inclusion in the qualitative synthesis and 16 articles were included in our meta-analysis. Articles eligible for pooled analyses included five working memory training (computerised cognitive training) studies with 236 participants, three goal management training (cognitive remediation) studies with 99 participants, four modafinil (cognitive enhancer) studies with 160 participants and four galantamine (cognitive enhancer) studies with 131 participants. Study duration ranged from 5 days to 13 weeks, with immediate follow-up assessments. There were no studies identified that specifically targeted gambling disorder. We only found evidence for a benefit on impulsive choice of goal management training, although only in two studies involving 66 participants (standardised mean difference (SMD) = 0.86; 95% CI = 0.49-1.23; P = 0.02; I²  = 0%, P = 0.95).

CONCLUSION

Cognitive remediation, and specifically goal management training, may be an effective treatment for addressing impulsive choice in addiction. Preliminary evidence does not support the use of computerised cognitive training or pharmacological enhancers to boost impulse control in addiction.

Are methamphetamine users compulsive? Faulty reinforcement learning, not inflexibility, underlies decision making in people with methamphetamine use disorder

Methamphetamine use disorder involves continued use of the drug despite negative consequences. Such 'compulsivity' can be measured by reversal learning tasks, which involve participants learning action-outcome task contingencies (acquisition-contingency) and then updating their behaviour when the contingencies change (reversal). Using these paradigms, animal models suggest that people with methamphetamine use disorder (PwMUD) may struggle to avoid repeating actions that were previously rewarded but are now punished (inflexibility). However, difficulties in learning task contingencies (reinforcement learning) may offer an alternative explanation, with meaningful treatment implications. We aimed to disentangle inflexibility and reinforcement learning deficits in 35 PwMUD and 32 controls with similar sociodemographic characteristics, using novel trial-by-trial analyses on a probabilistic reversal learning task. Inflexibility was defined as (a) weaker reversal phase performance, compared with the acquisition-contingency phases, and (b) persistence with the same choice despite repeated punishments. Conversely, reinforcement learning deficits were defined as (a) poor performance across both acquisition-contingency and reversal phases and (b) inconsistent postfeedback behaviour (i.e., switching after reward). Compared with controls, PwMUD exhibited weaker learning (odds ratio [OR] = 0.69, 95% confidence interval [CI] [0.63-0.77], p < .001), though no greater accuracy reduction during reversal. Furthermore, PwMUD were more likely to switch responses after one reward/punishment (OR = 0.83, 95% CI [0.77-0.89], p < .001; OR = 0.82, 95% CI [0.72-0.93], p = .002) but just as likely to switch after repeated punishments (OR = 1.03, 95% CI [0.73-1.45], p = .853). These results indicate that PwMUD's reversal learning deficits are driven by weaker reinforcement learning, not inflexibility.

Lack of longitudinal changes in cognition in individuals with methamphetamine use disorder during the first 6 weeks after commencing treatment

Background: Methamphetamine use disorder (MUD) associates with cognitive impulsivity deficits. However, few studies have examined longitudinal changes in cognition, and it remains unclear if deficits resolve during early recovery.Objectives: To compare: (1) cognitive function of individuals with MUD at treatment onset and six-weeks later with controls tested over the same period; (2) cognitive changes in MUD-individuals who remained abstinent versus relapsed.Method: We recruited 108 participants meeting DSM-IV-TR criteria for methamphetamine dependence (81 males) and 50 demographically matched controls (38 males); 77 methamphetamine- dependent participants (59 males) and 48 controls (36 males) were retained at follow-up. We administered response inhibition, delay discounting and uncertainty-based decision-making tests at both endpoints. Relapse was defined as methamphetamine concentrations >0.4 ng/mg at follow-up in hair toxicology.Results: We found a significant time-by-group interaction on uncertainty-based decision-making (effect size: η² = .05), although post-hoc tests to disentangle this interaction yielded inconclusive results (p-range = .14-.40; BF₁₀-range = 0.43-1.67). There were no significant time-by-group interactions on response inhibition or delay discounting, with the former likely a null effect (η²-interaction = .003 and .02; BF_incl = 0.23 and 0.71). There were no significant differences in cognitive recovery between individuals who maintained abstinence (n = 12) versus relapsed (n = 65) (η²-range = .003-.04), although evidence was inconclusive toward whether findings reflected true null effects (BF_incl-range = 0.33-0.75).Conclusion: We did not find evidence that MUD-related cognitive impulsivity deficits improve beyond practice effects over 6 weeks. Findings do not support previous, albeit conflicting, evidence of early recovery of cognitive deficits in MUD.

The natural history of the knee following arthroscopic medial meniscectomy

We examined the natural history of arthroscopic medial meniscectomy in knees with an isolated meniscal injury by reviewing 317 of 894 cases following medial meniscectomy. At the time of the initial surgery none of the knees had been operated on, and there was no evidence of ligament injury. The patients were reviewed clinically and radiologically after a mean of 11.5 years (range 10-15). The knee was considered "normal" or "nearly normal" by 91% of patients. In 218 patients the contralateral knee was asymptomatic without history of operation or significant injury and could be used as control for comparison. Radiology showed 22.4% greater excess prevalence of joint space narrowing in the operated compared to the control knee. The factors predisposing to a poor radiological result were age above 35 years, the presence of medial compartment cartilage degeneration at the time of the first arthroscopy, resection of the posterior one-third of the meniscus, and meniscal rim resection. Preoperative participation in sport was a predictor of a better outcome.

Is diagnostic arthroscopy of the hip worthwhile? A prospective review of 328 adults investigated for hip pain

We describe a prospective study of 328 patients undergoing arthroscopy of the hip. Arthrography, CT or MRI was performed when clinically indicated. A preoperative diagnosis was reached in 174 patients (53%), while the remaining 154 were diagnosed as having 'idiopathic hip pain'. In seven patients, access to the hip was inadequate. Arthroscopy altered the diagnosis in 176 hips (53%). The new primary diagnoses were osteoarthritis (75 patients), osteochondral defects (34), torn labra (23), synovitis (11) and loose bodies (9). In 172 hips (52%) an operative procedure was undertaken. In the remaining 84 patients (26%), arthroscopy neither changed the diagnosis nor provided surgical treatment. Arthroscopy of the hip is considered to be of value in assessing and treating the adult patient with pain in the hip of uncertain cause.

Is revision as good as primary hip replacement? A comparison of quality of life

Primary total hip arthroplasty (THA) is one of the most effective ways of improving quality of life (QoL). We have compared the improvement in QoL in 62 patients who had a cemented revision of a THA with that of 62 primary replacements. One year after operation the median QoL score had been significantly improved in both groups; from 0.870 to 0.990 in the primary group (p < 0.0001) and from 0.870 to 0.980 in the revised group (p < 0.0001). There was no significant difference in the improvement in scores between the groups (p = 0.29). When reviewed after four years there was no difference in the pain score for either group (p = 0.89), but that for function had deteriorated significantly. This was associated with revision surgery (p = 0.018) and a low preoperative QoL score (p = 0.004). We conclude that both primary and revision operations give a significant improvement in the QoL but function after revision may be less durable than after a primary arthroplasty.

Coregistration imaging of the foot. A new localisation technique

We describe a new technique, known as coregistration imaging, which superimposes 99mTc isotope bone scans on to plain radiographs. We used the technique selectively in cases in which the nuclear medicine physician, who reported the isotope scan, had difficulty in localising the anatomical site of the abnormality. In the forefoot, coregistration of isotope scans did not help to localise pathology; the scan alone gave sufficient detail. In 17 patients with pain in the hind- and midfoot, isotope scanning identified eight sites of abnormality in those with normal radiographs. In those with more than one abnormality on plain radiographs the isotope scan eliminated 12 sites of suspicion. Coregistration of the images significantly increased the certainty of localisation of disease (p < 0.001). We recommend the selective use of coregistration scanning as a useful technique for investigating patients with pain in the foot and ankle.

The 'dropping' and 'hornblower's' signs in evaluation of rotator-cuff tears

We studied 54 patients operated on for combined supraspinatus and infraspinatus rotator-cuff tears. The presence or absence of the dropping and hornblower's clinical signs of impaired external rotation were correlated with Goutallier stage-3 or stage-4 fatty degeneration of infraspinatus and teres minor. These grades of fatty degeneration have previously been correlated with a poorer outcome from reconstructive surgery. We found that hornblower's sign had 100% sensitivity and 93% specificity for irreparable degeneration of teres minor and the dropping sign 100% sensitivity and 100% specificity for similar degeneration of infraspinatus. In seven patients, teres minor showed hypertrophy. This muscle can give useful function for the activities of daily living in patients with rotator-cuff tears in whom it is intact.

De la Caffinière thumb carpometacarpal replacements. 93 cases at 6 to 16 years follow-up

The results of 93 de la Caffinière thumb joint replacements in 71 patients were reviewed between 6 and 16 years. The survival rate was 89% at 16 years. Eleven thumb joints had failed requiring revision. The commonest reason for failure was aseptic loosening of the trapezial component. The failure rate was higher in men of working age than any other group, which possibly reflects the increased demands on the prosthesis of these patients. We support the use of this implant for degenerative osteoarthritis, but caution against its use in men under 65 years.

Use of a laser guide to reduce screening time for the dynamic hip screw

A prospective, randomized study was used to evaluate a laser guide to aim the image intensifier during the treatment of 52 patients with intertrochanteric fractures of the proximal femur using a dynamic hip screw. The laser guide reduces the fluoroscopic screening time by 40 per cent (P < 0.05). We conclude that laser aiming of the image intensifier has a role in training radiographers, and reducing the dosage of irradiation in theatre procedures.

Vascularity of the neonatal femoral head: in vivo demonstration with power Doppler US

PURPOSE

To detect the intrinsic blood supply of the unossified neonatal femoral head in vivo by using power Doppler ultrasound (US) and to ascertain whether a reduction in blood flow could be demonstrated with hip abduction.

MATERIALS AND METHODS

One hip of 13 neonates was examined with power Doppler sonography. After vessels within the femoral head were identified, the thigh was slowly abducted and the angle at which flow became undetectable was recorded. Spectral Doppler tracings were obtained in all subjects.

RESULTS

Intrinsic blood flow of the femoral head was demonstrated in all subjects. Flow became undetectable during hip abduction in 11 of 13 neonates and reappeared during adduction. The angle at which flow became undetectable varied from 60 degrees to 85 degrees. Spectral Doppler signals demonstrated a mixed arterial and venous trace.

CONCLUSION

Power Doppler US provides a simple real-time assessment of the femoral head blood supply. This may prove helpful in identifying neonates at risk of avascular necrosis, a complication of treatment of hip dysplasia with abduction hip restraints.

Suction tip contamination in the ultraclean-air operating theatre

The surgical suction tip forms a reservoir for microorganisms during total hip replacement in conventional operating theatres. We assessed the colonisation of the tip in an ultraclean-air operating theatre in 39 patients, and found that 41% of them had evidence of bacterial colonisation with one or more bacteria. To avoid contamination we suggest that the suction tip is changed before preparation of the femoral canal and insertion of cement and prosthesis.

Multidimensional fourier transforms and image processing with finite scanning apertures

The Mertz and Gray analysis of image scanning in terms of multidimensional Fourier transforms is reformulated using a different coordinate system. A simplified mathematical notation is used for this analysis leading to scanning equations that emphasize the importance of the scanning apertures. Other image processes involving scanning are described in terms of their multidimensional Fourier transforms. These include a novel two-dimensional screening technique, and its comparison with a simple screening method and with conventional photographic screening processes. The effect on video spectra of aperture filtering and an analysis of television line interlacing are also given. The conditions for the validity of the unidimensional analysis of some of these image processing systems are indicated.

A Further Report on the Remarkable Series of Cases of Molluscum Fibrosum in Children communicated to the Society by Dr. John Murray in 1873

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