Conversational assessment using artificial intelligence is as clinically useful as depression scales and preferred by users

BACKGROUND

Depression is prevalent, chronic, and burdensome. Due to limited screening access, depression often remains undiagnosed. Artificial intelligence (AI) models based on spoken responses to interview questions may offer an effective, efficient alternative to other screening methods.

OBJECTIVE

The primary aim was to use a demographically diverse sample to validate an AI model, previously trained on human-administered interviews, on novel bot-administered interviews, and to check for algorithmic biases related to age, sex, race, and ethnicity.

METHODS

Using the Aiberry app, adults recruited via social media (N = 393) completed a brief bot-administered interview and a depression self-report form. An AI model was used to predict form scores based on interview responses alone. For all meaningful discrepancies between model inference and form score, clinicians performed a masked review to determine which one they preferred.

RESULTS

There was strong concurrent validity between the model predictions and raw self-report scores (r = 0.73, MAE = 3.3). 90 % of AI predictions either agreed with self-report or with clinical expert opinion when AI contradicted self-report. There was no differential model performance across age, sex, race, or ethnicity.

LIMITATIONS

Limitations include access restrictions (English-speaking ability and access to smartphone or computer with broadband internet) and potential self-selection of participants more favorably predisposed toward AI technology.

CONCLUSION

The Aiberry model made accurate predictions of depression severity based on remotely collected spoken responses to a bot-administered interview. This study shows promising results for the use of AI as a mental health screening tool on par with self-report measures.

Performance-based attentional control, but not self-reported attentional control, predicts changes in depressive symptoms in short-term psychotherapy

OBJECTIVE

Although impairments in attentional control are pervasive across psychopathology, there is substantial individual differences. In the current study, we examined whether individual differences in self-reported and performance-based measures of attentional control predict changes in depressive symptoms and well-being in a diagnostically diverse sample of patients attending a CBT-based partial hospital program.

METHOD

Participants were 89 patients (56.2% men, 75.3% non-Hispanic White). At baseline, patients completed the self-reported Attentional Control Scale and the Rapid Serial Visual Presentation task (RSVP), a behavioral measure of attentional control. Depressive symptoms were assessed daily using the Patient Health Questionnaire and well-being was assessed using the Mental Health Continuum Short Form.

RESULTS

On average, greater self-reported attentional control was significantly associated with lower depressive symptoms, β = -0.49, t(52) = 4.84, p < .001, 95% CIs [-0.69, -0.29], and greater well-being, β = 0.45, t(53) = 3.90, p < .001, 95% CIs [0.22, 0.67]. More accurate task-based performance was associated with a decline in depressive symptoms over time, β = -0.02, t(32) = 2.50, p = .02, 95% CIs [-0.04, -0.01]. Neither self-reported nor performance-based measures of attentional control predicted changes in well-being. Finally, exploratory analyses suggest that depressive symptoms also improved over time for individuals who underestimated self-reported attentional control abilities relative to task-based performance, β = -0.19, t(32) = 2.23, p = .03, 95% CIs [-0.36, -0.02].

CONCLUSIONS

Results suggest that performance-based attentional control may be an important target for assessment and intervention, as well as a potential mechanism underlying risk and recovery.

Measuring attentional blink magnitude: Reliability and validity of a novel single-target rapid serial visual presentation task index in a psychiatric sample

Rapid serial visual presentation (RSVP) tasks have been frequently used to assess attentional control in psychiatric samples; however, it is unclear whether RSVP tasks exhibits the psychometric properties necessary to assess these individual differences. In the current study, we examined the reliability and validity of single-target computerized RSVP task outcomes in a sample of 63 participants with moderate to severe psychiatric illness. At the group level, we observed the classical attentional blink phenomenon. At the individual level, conventional indices of attentional blink magnitude exhibited poor internal consistency. We empirically evaluated a novel index for assessing attentional blink magnitude using a single-target RSVP task that involves collapsing across experimental trials in which the attentional blink phenomenon occurs and disregarding performance on control trials, which suffer from ceiling effects. We found that this new index resulted in much improved reliability estimates. Both novel and conventional indices provided evidence of convergent validity. Consequently, this novel index may be worth examining and adopting for researchers interested in assessing individual differences in attentional blink magnitude.

Change in negative attention bias mediates the association between attention bias modification training and depression symptom improvement

OBJECTIVE

Attention bias modification training (ABMT) is purported to reduce depression by targeting and modifying an attentional bias for sadness-related stimuli. However, few tests of this hypothesis have been completed.

METHOD

The present study examined whether change in attentional bias mediated a previously reported association between ABMT condition (active ABMT, sham ABMT, assessments only; N = 145) and depression symptom change among depressed adults. The preregistered, primary measure of attention bias was a discretized eye-tracking metric that quantified the proportion of trials where gaze time was greater for sad stimuli than neutral stimuli.

RESULTS

Contemporaneous longitudinal simplex mediation indicated that change in attentional bias early in treatment partially mediated the effect of ABMT on depression symptoms. Specificity analyses indicated that in contrast to the eye-tracking mediator, reaction time assessments of attentional bias for sad stimuli (mean bias and trial level variability) and lapses in sustained attention did not mediate the association between ABMT and depression change. Results also suggested that mediation effects were limited to a degree by suboptimal measurement of attentional bias for sad stimuli.

CONCLUSION

When effective, ABMT may improve depression in part by reducing an attentional bias for sad stimuli, particularly early on during ABMT. (PsycInfo Database Record (c) 2021 APA, all rights reserved).

Rising to the Occasion of This COVID-19-Impacted Nation: Development, Implementation, and Feasibility of the Brief Assessment-Informed Skills Intervention for COVID-19 (BASIC)

The COVID-19 pandemic has had a profound impact on the global economy, physical health, and mental health. This pandemic, like previous viral outbreaks, has resulted in spikes in anxiety, depression, and stress. Even though millions of individuals face the physical health consequences of infection by COVID-19, even more individuals are confronted with the mental health consequences of this pandemic. This significantly increased demand for mental health services cannot be easily met by existing mental health systems, which often rely on courses of therapy to be delivered over months. Single session interventions (SSIs) may be one important approach to meeting this increased demand, as they are treatments designed to be delivered over the course of a single meeting. SSIs have been found to be effective for a range of mental health challenges, with durable effects lasting months to years later. Here, we describe an SSI designed for the COVID-19 pandemic. This Brief Assessment-informed Skills Intervention for COVID-19 (BASIC) program draws upon therapeutic skills from existing empirically supported treatments to target common presenting complaints due to this pandemic. We discuss the process of developing and implementing this intervention, as well as explore feasibility and initial clinical insights. In short, BASIC is an easy-to-adopt intervention that is designed to be effective in a single session, making it well-suited for handling the increased demand for mental health services due to COVID-19.

Efficacy of attention bias modification training for depressed adults: a randomized clinical trial

BACKGROUND

This study examined the efficacy of attention bias modification training (ABMT) for the treatment of depression.

METHODS

In this randomized clinical trial, 145 adults (77% female, 62% white) with at least moderate depression severity [i.e. self-reported Quick Inventory of Depressive Symptomatology (QIDS-SR) ⩾13] and a negative attention bias were randomized to active ABMT, sham ABMT, or assessments only. The training consisted of two in-clinic and three (brief) at-home ABMT sessions per week for 4 weeks (2224 training trials total). The pre-registered primary outcome was change in QIDS-SR. Secondary outcomes were the 17-item Hamilton Depression Rating Scale (HRSD) and anhedonic depression and anxious arousal from the Mood and Anxiety Symptom Questionnaire (MASQ). Primary and secondary outcomes were administered at baseline and four weekly assessments during ABMT.

RESULTS

Intent-to-treat analyses indicated that, relative to assessment-only, active ABMT significantly reduced QIDS-SR and HRSD scores by an additional 0.62 ± 0.23 (p = 0.008, d = -0.57) and 0.74 ± 0.31 (p = 0.021, d = -0.49) points per week. Similar results were observed for active v. sham ABMT: a greater symptom reduction of 0.44 ± 0.24 QIDS-SR (p = 0.067, d = -0.41) and 0.69 ± 0.32 HRSD (p = 0.033, d = -0.42) points per week. Sham ABMT did not significantly differ from the assessment-only condition. No significant differences were observed for the MASQ scales.

CONCLUSION

Depressed individuals with at least modest negative attentional bias benefitted from active ABMT.

Neurocognitive predictors of self-reported reward responsivity and approach motivation in depression: A data-driven approach

BACKGROUND

Individual differences in reward-related processes, such as reward responsivity and approach motivation, appear to play a role in the nature and course of depression. Prior work suggests that cognitive biases for valenced information may contribute to these reward processes. Yet there is little work examining how biased attention, processing, and memory for positively and negatively valenced information may be associated with reward-related processes in samples with depression symptoms.

METHODS

We used a data-driven, machine learning (elastic net) approach to identify the best predictors of self-reported reward-related processes using multiple tasks of attention, processing, and memory for valenced information measured across behavioral, eye tracking, psychophysiological, and computational modeling approaches (n = 202). Participants were adults (ages 18-35) who ranged in depression symptom severity from mild to severe.

RESULTS

Models predicted between 5.0-12.2% and 9.7-28.0% of held-out test sample variance in approach motivation and reward responsivity, respectively. Low self-referential processing of positively valenced information was the most robust, albeit modest, predictor of low approach motivation and reward responsivity.

CONCLUSIONS

Self-referential processing of positive information is the strongest predictor of reward responsivity and approach motivation in a sample ranging from mild to severe depression symptom severity. Experiments are now needed to clarify the causal relationship between self-referential processing of positively valenced information and reward processes in depression.

Examining differential relationships among self-reported attentional control, depression, and anxiety in a transdiagnostic clinical sample

BACKGROUND

Poor attentional control, defined as difficulty focusing attention on a task or shifting attention flexibly between tasks, is a transdiagnostic construct theorized to confer risk for, and maintain, depression and anxiety. Research to date in non-clinical samples has suggested a dissociable relationship between the two factors of self-reported attentional control and psychopathology, with depression being associated with difficulties shifting and anxiety being associated with focusing. However, to our knowledge no study has tested this differential set of relationships in a clinical sample.

METHODS

Adults (N = 493) presenting for psychiatric treatment completed measures of depressive and anxiety symptom severity and self-reported attentional control. Hierarchical linear regression and Zou's (2007) confidence interval method were used to examine the relationship between clinical symptoms and attentional control.

RESULTS

Both shifting and focusing were significantly correlated with anxiety and depressive symptoms in this sample. However, focusing was more strongly associated with clinical symptomatology than shifting, which showed a weak correlation.

LIMITATIONS

All constructs were measured cross-sectionally by self-report questionnaires.

CONCLUSIONS

In contrast to studies conducted in non-clinical samples, attentional focusing appears to be more relevant than attentional shifting in a clinical sample for both depression and anxiety symptoms. These findings lend support to efforts to develop neurocognitive interventions that improve focusing. Replication of these findings, particularly in longitudinal studies, is warranted.

Neural connectivity during affect labeling predicts treatment response to psychological therapies for social anxiety disorder

BACKGROUND

Although psychological treatments for social anxiety disorder (SAD) can be highly effective, many individuals do not respond to treatment. Identifying factors associated with improved outcomes can facilitate individualized treatment choices. We investigated whether patterns of neural connectivity predicted treatment responses and whether treatment type, cognitive behavioral therapy (CBT) or acceptance and commitment therapy (ACT), moderated this effect.

METHODS

Participants with SAD (n = 34) underwent fMRI prior to treatment and completed implicit and explicit emotion regulation tasks. Neural connectivity measures were estimates of amygdala-prefrontal cortex connectivity. Treatment responder status was defined using the 'clinically significant change index' (Loerinc et al., 2015).

RESULTS

Right amygdala-right ventrolateral prefrontal cortex connectivity during implicit emotion regulation was a significant predictor of treatment response (OR = 9.01, 95% CI = 1.77, 46.0, p = .008). Stronger inverse connectivity was associated with greater likelihood of treatment response. There were no significant neural moderators of treatment response to CBT versus ACT.

LIMITATIONS

The primary limitation of this work was the small sample size which restricted the power to detect significant moderation effects, and results should be interpreted as preliminary.

CONCLUSIONS

Amygdala-vlPFC connectivity during affect labeling predicted treatment responder status following CBT or ACT for social anxiety disorder. This suggests that the functioning of neural circuitry supporting emotion regulation capacities may be a 'gateway' to receiving benefit from psychological treatments. Future work should aim to replicate this effect in a larger sample and consider methods for enhancing functional connectivity within this circuitry as a potential treatment adjunct.

Attentional bias modification treatment for depression: Study protocol for a randomized controlled trial

Theoretical models and empirical research point to negatively biased attention as a maintaining factor in depression. Although preliminary studies suggest experimentally modifying attentional biases (i.e., attentional bias modification; ABM) reduces depression symptoms and depression risk, relatively few rigorous studies with clinical samples have been completed. This clinical trial examines the impact of ABM on a sample of adults (N = 123) with elevated depression severity who also exhibit at least modest levels of negatively biased attention prior to treatment. Participants will be randomly assigned to either active ABM, placebo ABM, or an assessment-only control condition. Individuals assigned to ABM will complete 5 trainings per week (2 in-clinic, 3 brief trainings at-home) during a four-week period. Throughout this four-week period, participants will complete weekly assessments of symptom severity and putative treatment mediators measured across different levels of analysis (e.g., eye tracking, behavioral measures, and functional Magnetic Resonance Imaging). This article details the rationale and design of the clinical trial, including methodological issues that required more extensive consideration. Our findings may not only point to an easily-accessible, efficacious treatment for depression but may also provide a meaningful test of whether a theoretically important construct, negatively biased attention, maintains depression.

Network analysis of depression and anxiety symptom relationships in a psychiatric sample

BACKGROUND

Researchers have studied psychological disorders extensively from a common cause perspective, in which symptoms are treated as independent indicators of an underlying disease. In contrast, the causal systems perspective seeks to understand the importance of individual symptoms and symptom-to-symptom relationships. In the current study, we used network analysis to examine the relationships between and among depression and anxiety symptoms from the causal systems perspective.

METHOD

We utilized data from a large psychiatric sample at admission and discharge from a partial hospital program (N = 1029, mean treatment duration = 8 days). We investigated features of the depression/anxiety network including topology, network centrality, stability of the network at admission and discharge, as well as change in the network over the course of treatment.

RESULTS

Individual symptoms of depression and anxiety were more related to other symptoms within each disorder than to symptoms between disorders. Sad mood and worry were among the most central symptoms in the network. The network structure was stable both at admission and between admission and discharge, although the overall strength of symptom relationships increased as symptom severity decreased over the course of treatment.

CONCLUSIONS

Examining depression and anxiety symptoms as dynamic systems may provide novel insights into the maintenance of these mental health problems.

Differential role of CBT skills, DBT skills and psychological flexibility in predicting depressive versus anxiety symptom improvement

OBJECTIVE

Studies have reported associations between cognitive behavioral therapy (CBT) skill use and symptom improvement in depressed outpatient samples. However, little is known regarding the temporal relationship between different subsets of therapeutic skills and symptom change among relatively severely depressed patients receiving treatment in psychiatric hospital settings.

METHOD

Adult patients with major depression (N = 173) receiving combined psychotherapeutic and pharmacological treatment at a psychiatric hospital completed repeated assessments of traditional CBT skills, DBT skills and psychological flexibility, as well as depressive and anxiety symptoms.

RESULTS

Results indicated that only use of behavioral activation (BA) strategies significantly predicted depressive symptom improvement in this sample; whereas DBT skills and psychological flexibility predicted anxiety symptom change. In addition, a baseline symptom severity X BA strategies interaction emerged indicating that those patients with higher pretreatment depression severity exhibited the strongest association between use of BA strategies and depressive symptom improvement.

CONCLUSIONS

Findings suggest the importance of emphasizing the acquisition and regular use of BA strategies with severely depressed patients in short-term psychiatric settings. In contrast, an emphasis on the development of DBT skills and the cultivation of psychological flexibility may prove beneficial for the amelioration of anxiety symptoms.

Validation of the PHQ-9 in a psychiatric sample

BACKGROUND

The PHQ-9 was originally developed as a screener for depression in primary care and is commonly used in medical settings. However, surprisingly little is known about its psychometric properties and utility as a severity measure in psychiatric populations. We examined the full range of psychometric properties of the PHQ-9 in patients with a range of psychiatric disorders (i.e., mood, anxiety, personality, psychotic).

METHODS

Patients (n=1023) completed the PHQ-9 upon admission and discharge from a partial hospital, as well as other self-report measures of depression, anxiety, well-being, and a structured diagnostic interview.

RESULTS

Internal consistency was good (α=.87). The PHQ-9 demonstrated a strong correlation with a well-established measure of depression, moderate correlations with related constructs, a weak correlation with a theoretically unrelated construct (i.e., disgust sensitivity), and good sensitivity to change, with a large pre- to post-treatment effect size. Using a cut-off of ≥13, the PHQ-9 demonstrated good sensitivity (.83) and specificity (.72). A split-half exploratory factor analysis/confirmatory factor analysis suggested a two-factor solution with one factor capturing cognitive and affective symptoms and a second factor reflecting somatic symptoms. Psychometric properties did not differ between male and female participants.

LIMITATIONS

No clinician-rated measure of improvement, and the sample lacked ethnoracial diversity.

CONCLUSIONS

This first comprehensive validation of the PHQ-9 in a large, psychiatric sample supported its use as a severity measure and as a measure of treatment outcome. It also performed well as a screener for a current depressive episode using a higher cut-off than previously recommended for primary care samples.

Who are gynandromorphophilic men? Characterizing men with sexual interest in transgender women

BACKGROUND

Gynandromorphophilia (GAMP) is sexual interest in gynandromorphs (GAMs; colloquially, shemales). GAMs possess a combination of male and female physical characteristics. Thus, GAMP presents a challenge to conventional understandings of sexual orientation as sexual attraction to the male v. female form. Speculation about GAMP men has included the ideas that they are homosexual, heterosexual, or especially, bisexual.

METHOD

We compared genital and subjective sexual arousal patterns of GAMP men with those of heterosexual and homosexual men. We also compared these groups on their self-ratings of sexual orientation and sexual interests.

RESULTS

GAMP men had arousal patterns similar to those of heterosexual men and different from those of homosexual men. However, compared to heterosexual men, GAMP men were relatively more aroused by GAM erotic stimuli than by female erotic stimuli. GAMP men also scored higher than both heterosexual and homosexual men on a measure of autogynephilia.

CONCLUSIONS

Results provide clear evidence that GAMP men are not homosexual. They also indicate that GAMP men are especially likely to eroticize the idea of being a woman.

Psychometric properties of the anxiety sensitivity index-3 in an acute and heterogeneous treatment sample

Anxiety sensitivity (AS) is associated with various forms of psychopathology. The most common measure of AS is the anxiety sensitivity index-3 (ASI-3). The current study examined the psychometric properties and factor structure of the ASI-3 in an acute and comorbid population seeking treatment for a broad range of psychopathology (N=382). Results confirmed a bi-factor structure and suggested that the ASI-3 demonstrates adequate psychometric properties in a transdiagnostic sample. The ASI-3 also showed adequate sensitivity to change over the course of partial hospital treatment. Findings regarding associations between specific anxiety disorders and subscales of the ASI-3 are discussed. Overall, the current results support the use of the ASI-3 to assess AS in heterogeneous treatment-seeking samples. This work is of particular utility for researchers examining the concept of AS transdiagnostically.

Properties of the Dialectical Behavior Therapy Ways of Coping Checklist in a Diagnostically Diverse Partial Hospital Sample

OBJECTIVE

Dialectical behavior therapy (DBT) was developed for treatment of borderline personality disorder (BPD), and adapted forms of DBT are currently used to treat bipolar disorder, eating disorders, anxiety, and depression. This study was designed to validate the Dialectical Behavior Therapy Ways of Coping Checklist (DBT-WCCL) DBT Skills subscale (DSS) for use in a diagnostically heterogeneous sample.

METHOD

We used naturalistic data from 228 patients receiving treatment at a partial hospital program to assess psychometric properties of the DBT-WCCL DSS. We assessed interitem correlations, internal consistency, factor structure, construct validity and sensitivity to change.

RESULTS

Internal consistency, construct validity, and sensitivity to change were good. The measure displayed good convergent and discriminant validity. Factor analysis results were consistent with previous research indicating a 1-factor solution for this subscale.

CONCLUSIONS

Psychometric properties were similar to the original BPD sample, indicating that this measure can be used as an assessment tool for DBT skill use in a diverse psychiatric population.

Abnormal error processing in depressive states: a translational examination in humans and rats

Depression has been associated with poor performance following errors, but the clinical implications, response to treatment and neurobiological mechanisms of this post-error behavioral adjustment abnormality remain unclear. To fill this gap in knowledge, we tested depressed patients in a partial hospital setting before and after treatment (cognitive behavior therapy combined with medication) using a flanker task. To evaluate the translational relevance of this metric in rodents, we performed a secondary analysis on existing data from rats tested in the 5-choice serial reaction time task after treatment with corticotropin-releasing factor (CRF), a stress peptide that produces depressive-like signs in rodent models relevant to depression. In addition, to examine the effect of treatment on post-error behavior in rodents, we examined a second cohort of rodents treated with JDTic, a kappa-opioid receptor antagonist that produces antidepressant-like effects in laboratory animals. In depressed patients, baseline post-error accuracy was lower than post-correct accuracy, and, as expected, post-error accuracy improved with treatment. Moreover, baseline post-error accuracy predicted attentional control and rumination (but not depressive symptoms) after treatment. In rats, CRF significantly degraded post-error accuracy, but not post-correct accuracy, and this effect was attenuated by JDTic. Our findings demonstrate deficits in post-error accuracy in depressed patients, as well as a rodent model relevant to depression. These deficits respond to intervention in both species. Although post-error behavior predicted treatment-related changes in attentional control and rumination, a relationship to depressive symptoms remains to be demonstrated.

Experimentally induced distraction impacts cognitive but not emotional processes in think-aloud cognitive assessment

Studies have examined the impact of distraction on basic task performance (e.g., working memory, motor responses), yet research is lacking regarding its impact in the domain of think-aloud cognitive assessment, where the threat to assessment validity is high. The Articulated Thoughts in Simulated Situations think-aloud cognitive assessment paradigm was employed to address this issue. Participants listened to scenarios under three conditions (i.e., while answering trivia questions, playing a visual puzzle game, or with no experimental distractor). Their articulated thoughts were then content-analyzed both by the Linguistic Inquiry and Word Count (LIWC) program and by content analysis of emotion and cognitive processes conducted by trained coders. Distraction did not impact indices of emotion but did affect cognitive processes. Specifically, with the LIWC system, the trivia questions distraction condition resulted in significantly higher proportions of insight and causal words, and higher frequencies of non-fluencies (e.g., “uh” or “umm”) and filler words (e.g., “like” or “you know”). Coder-rated content analysis found more disengagement and more misunderstanding particularly in the trivia questions distraction condition. A better understanding of how distraction disrupts the amount and type of cognitive engagement holds important implications for future studies employing cognitive assessment methods.

Neuropsychological deficits in major depression reflect genetic/familial risk more than clinical history: a monozygotic discordant twin-pair study

Neuropsychological deficits have been associated with major depression (MD) and persist in some individuals even after symptom remission. However, it is unclear if the deficits are a consequence of MD or are pre-existing and reflect MD vulnerability. We addressed this issue by studying 117 twins from monozygotic (MZ) pairs discordant for lifetime history of DSM-III-R defined MD and 41 twins from MZ pairs in which neither twin had experienced MD. Our assessment included a structured clinical interview and measures from the WMS-III and WAIS-III. The "unaffected" twins from discordant pairs showed the same pattern of performance as their affected cotwins on measures of attention, working memory, verbal memory, and visuo-spatial processing. Compared to twins from pairs with no MD history, twins in discordant pairs had lower performance in the domains of attention, memory, visuo-spatial processing, and general knowledge. However, after adjusting for sex and age, the groups differed only on attention and general knowledge. The similar performance of twins in pairs discordant for MD suggests that familial risk for MD has a greater influence on neuropsychological functioning than individual MD history. Findings of impairment in individuals euthymic for MD are more consistent with pre-existing deficits than scarring effects of MD.

Geophysical, archaeological, and historical evidence support a solar-output model for climate change

Although the processes of climate change are not completely understood, an important causal candidate is variation in total solar output. Reported cycles in various climate-proxy data show a tendency to emulate a fundamental harmonic sequence of a basic solar-cycle length (11 years) multiplied by 2(N) (where N equals a positive or negative integer). A simple additive model for total solar-output variations was developed by superimposing a progression of fundamental harmonic cycles with slightly increasing amplitudes. The timeline of the model was calibrated to the Pleistocene/Holocene boundary at 9,000 years before present. The calibrated model was compared with geophysical, archaeological, and historical evidence of warm or cold climates during the Holocene. The evidence of periods of several centuries of cooler climates worldwide called "little ice ages," similar to the period anno Domini (A.D.) 1280-1860 and reoccurring approximately every 1,300 years, corresponds well with fluctuations in modeled solar output. A more detailed examination of the climate sensitive history of the last 1, 000 years further supports the model. Extrapolation of the model into the future suggests a gradual cooling during the next few centuries with intermittent minor warmups and a return to near little-ice-age conditions within the next 500 years. This cool period then may be followed approximately 1,500 years from now by a return to altithermal conditions similar to the previous Holocene Maximum.

Hydrogen and deuterium loss from the terrestrial atmosphere: a quantitative assessment of nonthermal escape fluxes

A comprehensive one-dimensional photochemical model extending from the middle atmosphere (50 km) to the exobase (432 km) has been used to study the escape of hydrogen and deuterium from the Earth's atmosphere. The model incorporates recent advances in chemical kinetics as well as atmospheric observations by satellites, especially the Atmosphere Explorer C satellite. The results suggest: (1) the escape fluxes of both H and D are limited by the upward transport of total hydrogen and total deuterium at the homopause (this result is known as Hunten's limiting flux theorem); (2) about one fourth of total hydrogen escape is thermal, the rest being nonthermal; (3) escape of D is nonthermal; and (4) charge exchange and polar wind are important mechanisms for the nonthermal escape of H and D, but other nonthermal mechanisms may be required. The efficiency to escape from the terrestrial atmosphere for D is 0.74 of the efficiency for H. If the difference between the D/H ratio measured in deep-sea tholeiite glass and that of standard sea water, delta D = -77%, were caused by the escape of H and D, we estimate that as much water as the equivalent of 36% of the present ocean might have been lost in the past.