Sluggish Cognitive Tempo,Internalizing Symptoms,and Executive Function in Adults With ADHD

Abstract

Objective: We sought to characterize relationships between sluggish cognitive tempo (SCT) and both internalizing symptoms and executive functioning in adults with ADHD. Method: A total of 102 adults with ADHD completed clinical interviews and clinical rating scales. Hierarchical regression analyses were conducted to ascertain the independent predictive power of SCT symptoms for deficits in executive function (EF) after considering severity of ADHD inattentive and hyperactive-impulsive symptoms and internalizing symptoms. Results: SCT correlated with ADHD inattentive symptoms and dimensional measures of depression and anxiety but not with clinical diagnosis of depression or anxiety. SCT predicted EF deficits over and above the effects of internalizing and ADHD symptoms. This relationship between SCT and EF was limited to the subset of participants (n = 48) receiving stimulant treatment. Conclusion: SCT in adults with ADHD is associated with internalizing symptoms, ADHD inattentive symptoms, and, independently, with EF deficits. Further research is needed to ascertain why this relationship occurred primarily in adults concurrently receiving stimulants.

Keywords

ADHD sluggish cognitive tempo depression anxiety executive function

Sluggish cognitive tempo (SCT) is a term for a cluster of symptoms that includes hypoactivity, drowsiness, daydreaminess, lethargy, and apathy, and that has been proposed to better characterize the clinical presentation of a subgroup of those with attention and concentration problems (Carlson, Lahey, & Neeper, 1986; McBurnett, Pfiffner, & Frick, 2001). SCT was considered for inclusion as a symptom domain of the Predominantly Inattentive subtype in the Diagnostic and Statistical Manual of Mental Disorders (4th ed.; DSM-IV; American Psychiatric Association [APA], 1994). Two symptoms were tested (“drowsy” and “daydreams”) and were ultimately not included because they were found to have high positive but low negative predictive validity for the Inattentive dimension in the DSM-IV field trials (Frick et al., 1994). A third symptom, forgetfulness, was also considered as a potential SCT symptom but was found to have both positive and negative predictive validity, and so was included as an ADHD inattentive symptom in DSM-IV.

Early factor analytic research revealed that SCT symptoms constituted a factor distinct from that of the inattentive and hyperactive-impulsive symptoms of ADHD, and suggested that elevations on this factor uniquely characterized the ADHD, Predominantly Inattentive (ADHD-I) subtype (McBurnett et al., 2001). Subsequent research partially corroborated these results, establishing that symptoms of SCT, as rated by parents and teachers, emerged as a separate, third factor when entered into analyses that included ratings of inattentive and hyperactive-impulsive symptoms of ADHD (Becker, Langberg, Luebbe, Dvorsky, & Flannery, 2014; Garner, Marceaux, Mrug, Patterson, & Hodgens, 2010; Lee, Burns, Snell, & McBurnett, 2014; Willcutt et al., 2014). A recent meta-analysis, considering 23 independent studies including 19,000 participants, has confirmed that SCT constitutes a factor distinct both from the ADHD-I and ADHD Hyperactive-Impulsive (ADHD-HI) symptom dimensions (Becker et al., 2016). In addition and as predicted, given the nature of the symptoms, SCT has been shown in several studies in children and in a recent meta-analysis to correlate more highly with the inattentive than the hyperactive-impulsive dimension of ADHD (Becker et al., 2016; Frick et al., 1994; Lee et al., 2014).

The relationship of SCT to ADHD-I is not yet fully clear, however, with some studies not only finding higher SCT ratings in ADHD-I than ADHD, Combined (ADHD-C) presentation (Garner et al., 2010; Willcutt et al., 2014) but also finding that ADHD-C had higher SCT ratings than did the controls (Willcutt et al., 2014). Moreover, dividing ADHD-I into subgroups with high versus low SCT symptoms did not yield corresponding differences in gender, age of onset, or parent ratings of internalizing or externalizing symptomatology (Harrington & Waldman, 2010). Rather unexpectedly, Barkley (2013) found more frequent cases of high SCT among children and adolescents with ADHD-C (55%) when compared with those with ADHD-I (31%) or ADHD-HI presentation (21%). Intriguingly, recent studies of community samples of children (Barkley, 2013) and adults (Barkley, 2012b) found that high SCT occurred in some participants in the absence of ADHD, which, the authors suggested, may indicate that SCT represents a separate disorder with high overlap with ADHD, rather than a subtype of ADHD. In summary, SCT symptoms appear to have a greater association with inattentive than with hyperactive/impulsive symptoms, but do not aid in differentiating ADHD-I from ADHD-C.

SCT and Internalizing Symptoms in Children and Adolescents

Research in children and adolescents has also addressed the possibility that SCT is a manifestation of anxiety or depression, which it phenotypically resembles. Symptoms of SCT emerged as a separate factor even when entered into analyses that included symptoms of anxiety and depression in addition to those of ADHD, indicating that SCT is not simply a proxy for these internalizing disorders in children (Willcutt et al., 2014). This finding was confirmed in meta-analysis (Becker et al., 2016). However, SCT does appear to co-occur with internalizing disorders in children with a greater frequency than does ADHD alone (Garner et al., 2010; Lee et al., 2014; Willcutt et al., 2014). Furthermore, the presence of SCT predicted internalizing symptoms and social problems even after controlling for its association with ADHD symptomatology (Becker & Langberg, 2013; Marshall, Evans, Eiraldi, Becker, & Power, 2014). In a study of children, inattentive ADHD symptoms and parent-reported depression were uniquely associated with SCT symptoms, but child-reported depression did not carry an independent association with SCT (Garner, Mrug, Hodgens, & Patterson, 2013). Barkley (2013) compared groups of children/adolescents with SCT-only, ADHD-only, ADHD + SCT, and typical children and found that the two groups with SCT had higher rates of depression than typical children, which was not true for the ADHD-only group. The SCT groups did not, however, have higher rates of anxiety (Barkley, 2013). The conclusion thus far is that there is an association between SCT and internalizing disorders, particularly depression, but that they are not completely overlapping constructs.

SCT and Executive Function (EF) in Children and Adolescents

Several studies have examined the extent to which SCT contributes to the prediction of EF deficits in youth after accounting for inattentive symptoms. Using parent ratings on the Barkley Deficits in Executive Functioning Scale–Children and Adolescents (BDEFS-CA), a questionnaire measure of EF, Barkley showed that the set of Diagnostic and Statistical Manual of Mental Disorders (5th ed.; DSM-5; APA, 2013) ADHD inattentive symptoms explained by far the greatest proportion of the variance, with SCT contributing only a very small additional percentage—approximately 5% of the variance on the self-organization/problem-solving dimension (Barkley, 2012a, 2013). Similar results were reported by Becker and Langberg (2014), in a study of 52 adolescents with ADHD using the Metacognitive Index of the teacher- and parent-rated Behavior Rating Inventory of Executive Function (BRIEF), which encompasses initiation, working memory, planning, organization, and self-monitoring (Gioia, Isquith, Guy, & Kenworthy, 2000). On the contrary, a Spanish study of 76 youth aged 6 to 17 years found that correlations between SCT and several EF domains measured on the BRIEF (emotional control, working memory, planning/organization, and organization of materials) remained significant after controlling for ADHD symptoms (Araujo Jiménez, Jané Ballabriga, Bonillo Martin, Arrufat, & Serra Giacobo, 2015). None of these three studies accounted for the effects of depression and anxiety in their regression analyses, but all found a modest independent correlation between SCT and some, but not all, domains of EF.

Among studies that did consider internalizing comorbidity, a study of 165 children aged 7 to 11 years with ADHD-I found a correlation between organization problems measured by the Children’s Organizational Skills Scale and one of the three SCT factors—“sleepy/tired”—that remained significant after partialing out the effect of depression severity across both parent and teacher reports (Abikoff et al., 2013; McBurnett et al., 2014). A smaller study of children aged 7 to 12 years compared 19 children with ADHD-I and SCT with 68 children with ADHD but not SCT—and reported that children with SCT and ADHD-I had fewer problems with sustained attention but greater problems with EF as measured by the BRIEF (Capdevila-Brophy et al., 2014). After adjusting for anxiety and depression, only the relationship between high SCT and deficits in self-monitoring remained stronger than in the low SCT group.

Contrasting with these findings are the results of several large studies using neuropsychological test measures of EFs, which did not find significant correlations with SCT (Bauermeister, Barkley, Bauermeister, Martinez, & McBurnett, 2012; Wahlstedt & Bohlin, 2010; Willcutt et al., 2014).

In summary, studies measuring EFs using self-report rating scales in children and young adults tend to find a relationship with SCT, though generally a weaker relationship than that between EF and ADHD-I symptoms. This relationship is not found when using neuropsychological tests of EF, which may reflect the lesser ecological validity of EF tests compared with EF rating scales in both children (Isquith, Roth, & Gioia, 2013) and adults (Barkley & Fischer, 2011; Barkley & Murphy, 2010).

SCT in Adults

Several studies have examined the relationship between SCT and EF in large samples of undergraduate psychology college students, and two have studied adults beyond college age. In a study of 768 college students, SCT emerged as a separate factor, independent of ADHD symptoms (Becker et al., 2014), and was associated with depression and anxiety in another study of 158 students (Flannery, Becker, & Luebbe, 2016). Furthermore, SCT predicted unique variance in social impairment, an effect that was mediated via emotional dysregulation (Flannery et al., 2016). Interestingly, Wood reported that high SCT occurred without ADHD in 9.8% of their sample of 458 students (Wood, Lewandowski, Lovett, & Antshel, 2014), consistent with the possibility that SCT may exist as a separate disorder.

Two studies examined the relationship between SCT and EF in large samples of college students (Jarrett, Rapport, Rondon, & Becker, 2017; Wood et al., 2014). Symptoms of ADHD, depression, anxiety, as well as EF and SCT were assessed via self-report. Both studies showed that SCT contributed unique variance to EF subscales of self-organization/problem solving and emotional self-regulation on the Barkley Deficits in Executive Function Scale (BDEFS; Jarrett et al., 2014), whereas ADHD inattentive symptoms more strongly predicted self-management to time. SCT contributed to the Total EF score more than (Wood et al., 2017) or equally (Jarrett et al., 2017) with ADHD-I. Jarrett et al. (2017) also tested participants on visual working memory, set-shifting, and attention and found no relationship between these neuropsychological test results and either SCT or ADHD symptoms.

Only two studies of which we are aware have studied SCT in adults beyond college age. In one, Barkley (2012b) recruited a representative sample of 1,249 U.S. adults, 18-96 years of age. Participants were divided into those with and without ADHD (on the basis of a self-rated scale of DSM-IV ADHD symptoms) and those high and low in SCT (based on a nine-item self-rated scale comprised of items from earlier studies of children). This procedure identified 46 participants with ADHD but without SCT, and 39 with both ADHD and SCT. A subgroup of 33 were found to have SCT but not ADHD, corroborating findings in youth that suggested that SCT may occur without ADHD (Barkley, 2013). As was reported for children, SCT did not appear to sort strictly with the ADHD-I subtype, occurring in 68% of those with ADHD-I, 65% of those with ADHD-C, and 10% of those with ADHD-HI. Self-reported occupational impairment was higher in those with SCT-only than in those with ADHD-only, and highest in those with both. Educational impairment was equivalent in those with SCT, with or without ADHD, and higher than in those with ADHD-only. More clearly than in youth, SCT conferred impairment in EF (on the BDEFS) over and above that associated with ADHD. Specifically, those with both ADHD and SCT were more impaired in time management, self-organization, self-restraint (inhibition), regulation of emotion, and motivation than were those with ADHD or SCT alone.

A second study found a negative association between SCT and quality of life in a nonclinical, community sample of 983 adults (Combs, Canu, Broman Fulks, & Nieman, 2014). Although this study did not assess EF directly, the broad quality of life measure suggested the presence of functional impairment. These results, taken together, suggest that the symptoms of SCT negatively affect EF more in adults than in youth. However, the relationship with internalizing disorders is not yet clear.

In summary, although SCT is relatively well studied in children and adolescents, there is a paucity of data concerning ADHD in adults, particularly with respect to relationships with internalizing disorders and with executive functioning. Furthermore, as research to date in adults has measured SCT in population- or community-based samples, it is particularly important to examine these issues in clinically referred and comprehensively evaluated adults.

We therefore tested the following hypotheses to better characterize SCT in a sample of clinically referred and diagnosed adults with ADHD: Given the nature of SCT and given previous research in children, we postulated that SCT would be more highly correlated with the inattentive dimension of ADHD symptoms than with the hyperactive/impulsive dimension. Based on studies in youth, and on our own clinical observations, we predicted that among clinically diagnosed adult participant with ADHD and high SCT, there would be a higher percentage of ADHD-I than among those with ADHD and low SCT. We predicted that adults with ADHD and high SCT scores would have both higher rates of clinical diagnosis of depression or anxiety and higher scores on dimensional ratings of internalizing disorders compared with adults with ADHD and low SCT scores. Finally, we hypothesized that SCT would predict greater impairments in EFs after controlling for severity of ADHD symptoms and internalizing symptomatology.

Method

Participants were drawn from among adults referred to and comprehensively evaluated at a specialty service for ADHD at a tertiary referral medical center in an urban setting of a large metropolitan area. The institutional review board (IRB) at the medical center approved the study. Participants constituted all individuals evaluated between August 2012 and March 2014, who met criteria for a DSM-IV or DSM-5 diagnosis of ADHD via two unstructured clinical interviews that established current and lifetime symptoms of ADHD and other possible differential or comorbid diagnoses. In the first visit, evaluators ascertained current symptoms, context, and impairment. In the second, they obtained developmental, academic, and social history from childhood through adulthood to examine onset and trajectory of symptoms of ADHD and any other presenting symptoms (and associated impairment) to determine the relative primacy of ADHD and comorbid symptoms. Evaluations were performed by experienced staff clinicians. Most interviews were conducted prior to release of DSM-5, therefore Diagnostic and Statistical Manual of Mental Disorders (4th ed., text rev.; DSM-IV-TR; APA, 2000) definitions were used. The DSM-based clinical diagnosis of ADHD was corroborated by a T-score equal to or greater than 63 (i.e., 1.3 standard deviation above the mean) on the subscale Conners’ Adult ADHD Rating Scale (CAARS), DSM-IV Inattentive Symptoms Subscale E (CAARS-E). Study subjects did not include any participant with history of schizophrenia, bipolar disorder, or borderline personality disorder; history of neurological disorders such as epilepsy, mental retardation, or traumatic brain injury; active substance abuse; or report of active suicidal ideation. Of evaluated participants, one was deemed ineligible due to diagnosis of thought disorder (judged equivalent to psychotic disorder, not otherwise specified), and one for a history of traumatic brain injury. No evaluated participants met criteria for other exclusionary diagnoses. Eighteen participants were excluded because they did not meet ADHD and/or CAARS-E inclusion criteria.

A depressive disorder was counted as present if a participant met criteria for any of the disorders that fall within the Depressive Disorders category in DSM-5 except Depressive Disorder Due to Another Medical Condition or Substance/Medication-Induced Depressive Disorder. Similarly, an anxiety disorder was counted as present if a participant met criteria for any of the disorders that fall within the Anxiety Disorders category in DSM-5 except Anxiety Disorder Due to Another Medical Condition or Substance/Medication-Induced Anxiety Disorder. All participants completed the following clinical rating scales: the CAARS, from which two subscales were used for this study—CAARS-E and Subscale F, DSM-IV Hyperactive-impulsive symptoms (CAARS-F; Conners, Erhart, & Sparrow, 1999); Barkley’s nine-item SCT rating scale (Barkley, 2012a); the Beck Depression Inventory–II (BDI-II; Beck, Steer, & Brown, 1996); and State-Trait Anxiety Inventory (STAI; Spielberger, Gorsuch, Vagg, & Jacobs, 1983) as dimensional measures of internalizing disorder symptoms; and the BDEFS self-report, from which all subscales were used: self-management to time, self-organization/problem solving, self-motivation, self-regulation of emotions, Total EF, and ADHD-EF index—this last, index subscale indicates the likelihood that the respondent has ADHD (Barkley, 2011).

All data analyses were conducted using SPSS software, Version 23. SCT was examined both as a categorical variable and as a continuous/dimensional variable. For SCT as a categorical variable, an SCT symptom was considered to be present if rated as 2 (pretty much) or 3 (very much) on a scale of 0 to 3. Those with five or more symptoms were considered “high SCT.” The validity of this division is supported by the fact that it matched the criterion identified as the 95th percentile for SCT symptom burden in a recent large, nonclinical sample of adults, and therefore was used as a cutoff for high SCT in that study (Barkley, 2012b). High and low SCT groups were compared based on demographic characteristics and categorical diagnoses using Pearson’s chi-square.

Pearson’s correlations were conducted to examine the relationships among SCT, ADHD symptoms, internalizing symptoms, and executive dysfunction. Hierarchical linear regression was conducted to ascertain the predictive utility of SCT vis-à-vis executive dysfunction after considering the contributions of ADHD symptoms and internalizing symptoms. Independent variables were forced into the analysis in the following order: Block 1: Age, Block 2: DSM-IV Inattentive symptoms (CAARS-E), Block 3: DSM-IV Hyperactive-impulsive symptoms (CAARS-F), Block 4: Internalizing symptoms as captured in the total scores on the BDI-II and State/Trait Anxiety Indices, and Block 5: SCT. A separate model was constructed for each of the BDEFS EF subscales. In addition, we repeated the regression analyses after splitting the sample by those taking and not taking stimulants at the time of evaluation due to the possibility that stimulant use may affect the relationship between SCT and EF.

Results

Demographic statistics are reported in Table 1. The final sample consisted of 102 participants ranging in age from 18 to 64 years (M = 37.8, SD = 11.6), of whom 48 had a symptom score less than 5 and were considered “low SCT.” The remaining 54 participants were considered “high SCT.” The mean SCT score in the “low SCT” group was 10.08 (SD = 3.0), while the mean SCT score of the “high SCT” group was 18.41 (SD = 3.36). In the sample as a whole, 62 (61%) were classified as ADHD-I and 37 (36%) as ADHD-C. One participant had ADHD-HI and two had Unspecified ADHD. Most participants (93%) self-identified as Caucasian, and 81% had at least a bachelor’s degree. The high SCT group participants were significantly younger than the low SCT group: mean age was 34.69 years (SD = 10.5) versus 41.25 years (SD = 11.8), respectively, t(100) = 2.97, p = .004. Age was therefore used as a covariate in subsequent analyses. The high SCT group also had significantly fewer advanced degrees, but this was not included as a covariate because it was judged likely to be an outcome of SCT, given the previously reported functional impairments in adults (Barkley, 2012b; Combs et al., 2014). The groups did not differ significantly in gender, race/ethnicity, or marital status.

Table 1.

Demographic Characteristics.

Characteristic	Frequency (%)		Pearson χ	p
Characteristic	High SCT (n = 54)	Low SCT (n = 48)	Pearson χ	p
Gender			1.18	.278
Male	28 (52%)	30 (63 %)
Female	26 (48%)	18 (37%)
Race/ethnicity			5.75	.218
Asian	1 (2%)	3 (6%)
Black, non-Hispanic	1 (2%)	1 (2%)
Black, Hispanic	0	0
White, non-Hispanic	51 (94%)	41 (86%)
White, Hispanic	0	3 (6%)
Multiple	1 (2%)	0
Education			13.19	.033
High school or equivalent	10 (19%)	8 (17%)
Technical	1 (2%)	0
Bachelor’s	32 (59%)	17 (35%)
Master’s	8 (15%)	10 (21%)
Doctorate or professional	3 (5%)	12 (25%)
Unknown	0	1 (2%)
Marital status			3.42	.332
Married	22 (41%)	27 (57%)
Divorced	4 (7%)	2 (4%)
Never married	26 (48%)	16 (33%)
Cohabiting	2 (4%)	3 (6%)

Note. SCT = sluggish cognitive tempo.

High and low SCT groups were compared with respect to proportions of ADHD subtype diagnoses and of comorbid internalizing disorder diagnoses (Table 2). Rates of ADHD subtypes were closely comparable in the two groups: 41% and 31% for ADHD-C in the high and low SCT groups, respectively, versus 59% and 63% for ADHD-I. There was no significant difference between the low and high SCT groups in the proportions of individuals with depressive or anxiety disorders.

Table 2.

Frequencies of ADHD and Internalizing Diagnoses in High and Low SCT Groups.

DSM diagnosis	Frequency (%)		Pearson χ²	p
DSM diagnosis	High SCT (n = 54)	Low SCT (n = 48)	Pearson χ²	p
ADHD subtype			4.05	.256
Combined	22 (41%)	15 (31%)
Predominantly inattentive	32 (59%)	30 (63%)
Hyperactive-impulsive	0	1 (2%)
Unspecified	0	2 (4%)
Internalizing disorders
Depressive disorder	22 (41%)	16 (33%)	0.60	.440
Anxiety disorder	18 (33%)	12 (25%)	0.85	.357
Depressive or anxiety disorder	24 (44%)	20 (42%)	0.08	.777

Note. SCT = sluggish cognitive tempo; DSM = Diagnostic and Statistical Manual.

Results of hierarchical multiple regression analyses are presented in Table 3. Standardized beta coefficients associated with the full model equation for each BDEFS variable are presented in Table 4. All variance inflation factor (VIF) values indicated acceptable levels of multicollinearity (1 < VIF < 4 for all independent variables across all models). Significance of the change in F (Table 3) indicated that, after entering age, CAARS-E contributed significantly to the models for all BDEFS subscales and indices. CAARS-F added additional variance to the equations for self-organization/problem solving, self-restraint, and self-regulation of emotions. The internalizing scales, entered next, contributed significant variance to self-motivation, self-regulation of emotions, and Total EF, but not to the ADHD-EF Index. Finally, and most importantly for our hypotheses, both the significance of change in F values (Table 3) and the standardized coefficients (Table 4) indicated that SCT contributed unique variance to the measurement of self-organization/problem solving and Total EF summary score, but not to the other subscales of time management, self-restraint, self-motivation, or the index score. This pattern of results held true whether SCT was entered before or after entry of internalizing symptoms (not shown). When entered last in the model, after SCT, internalizing symptomatology continued to significantly predict self-motivation and self-regulation; however, it no longer predicted to Total EF, indicating that SCT accounted for more of the variance in Total EF.

Table 3.

Hierarchical Multiple Regression Models Predicting BDEFS Subscale Scores From Age, CAARS-E (DSM-IV Inattentive), BDI-II, STAI State/Trait, and SCT Scores.

Predictor	Self-management to time	Self-organization/problem solving	Self-restraint	Self-motivation	Self-regulation of emotions	Total EF	ADHD Index
Age
R²	.07	.02	.00	.00	.00	.01	.03
ΔF	6.33*	2.10	0.01	0.00	0.11	.47	2.18
df1,2	1,84	1,84	1,84	1,84	1,84	1,84	1,80
ADHD-I
R²	.13	.14	.16	.06	.11	.13	.13
ΔF	5.89*	11.30**	15.22***	5.59*	10.30**	12.07**	9.43**
df1,2	1,83	1,83	1,83	1,83	1,83	1,83	1,79
ADHD-HI
R²	.15	.19	.38	.07	.21	.13	.16
ΔF	1.51	5.40*	29.05***	0.22	9.73**	0.13	2.71
df1,2	1,82	1,82	1,82	1,82	1,82	1,82	2,78
Internalizing scales
R²	.18	.22	.39	.17	.42	.22	.22
ΔF	1.08	0.72	0.78	3.30*	9.66***	2.87*	1.88
df1,2	3,79	3,79	3,79	3,79	3,79	3,79	3,75
SCT
R²	.19	.28	.40	.17	.42	.26	.22
ΔF	0.53	6.86*	1.11	0.03	0.63	4.15*	0.57
df1,2	1,78	1,78	1,78	1,78	1,78	1,78	1,74

Note. Sample size for all analyses is 86 except for BDEFS ADHD-EF Index, for which sample size is 82. Internalizing scales are the BDI-II and STAI. BDEFS = Barkley Deficits in Executive Functioning Scale; CAARS-E = Conners’ Adult ADHD Rating Scale DSM-IV Inattentive Symptoms Subscale E; BDI-II = Beck Depression Inventory–II; STAI = State-Trait Anxiety Inventory; SCT = sluggish cognitive tempo; EF = executive function; ADHD-I = Conners’ Adult ADHD Rating Scale Self-Report Long Form Subscale E, DSM-IV Inattentive Symptoms; ADHD-HI = Self-Report Long Form Subscale F: DSM-IV Hyperactive-Impulsive Symptoms; DSM = Diagnostic and Statistical Manual.

†

p < .10. *p < .05. **p < .01. ***p < .001.

Table 4.

Standardized Beta Values for Variables in Full Hierarchical Regression Model Predicting BDEFS Subscale Scores From Age, ADHD Symptoms, Internalizing Symptoms, and SCT.

Predictor	BDEFS subscale
Predictor	Self-management to time	Self-organization/problem solving	Self-restraint	Self-motivation	Self-regulation of emotions	Total EF summary score	ADHD-EF index
Age	.24*	.17^†	.001	−.04	.03	.08	.17
ADHD-I	.27*	.33**	.20^†	.28*	−.01	.19	.14
ADHD-HI	−.14	−.26*	.50***	−.06	.29**	.01	.16
BDI-II	.22	.08	.03	.43**	.01	.13	−.09
STAI-State	−.19	.08	.16	−.39*	.17	−.18	.25
STAI-Trait	.04	−.08	−.03	.04	.34*	.26	.07
SCT Total	.09	.29*	−.11	.02	.08	.23*	.09
Total R²	.19	.28	.40	.17	.42	.26	.22

Note. Sample size for all analyses is 86 except for BDEFS ADHD-EF Index, for which sample size is 82. BDEFS = Barkley Deficits in Executive Functioning Scale; SCT = sluggish cognitive tempo; EF = executive function; ADHD-I = Conners’ Adult ADHD Rating Scale Self-Report Long Form Subscale E, DSM-IV Inattentive Symptoms; ADHD-HI = Conners’ Adult ADHD Rating Scale Self-Report Long Form Subscale F: DSM-IV Hyperactive-Impulsive Symptoms; DSM = Diagnostic and Statistical Manual; BDI-II = Beck Depression Inventory–II; STAI = State-Trait Anxiety Inventory.

†

p < .10. *p < .05. **p < .01. ***p < .001.

Inspection of the standardized coefficients (Table 4) indicates that among the internalizing scales, BDI-II and STAI-State have significant predictive power for self-motivation (STAI-State in the negative direction) whereas STAI-Trait has significant predictive power for self-regulation of emotions. Partial correlations were conducted to ascertain with which internalizing variables SCT was most highly correlated. Results revealed significant correlations between SCT and STAI-Trait after controlling for STAI-State and BDI-II (r = .23, p = .026). Furthermore, correlations between SCT and BDI-II and STAI-State were each nonsignificant after controlling for the other internalizing scale, indicating that the primary comorbidity between SCT and internalizing symptoms is with trait anxiety.

We found that 48 (47%) of the sample reported taking stimulants at the time of evaluation, while 54 (53%) of the sample did not. The groups did not differ significantly in age, gender, race/ethnicity, educational level, marital status, or proportion of DSM subtype or frequency of depression or anxiety disorders. The groups differed significantly in CAARS-E and BDEFS self-regulation of emotions scores but not on any other clinical rating scales. The group reporting stimulant use had a mean CAARS-E score of 78.2 (SD = 8.1), while the group not reporting stimulant use had a mean score of 81.7 (SD = 8.1, p = .029). The group reporting stimulant use had a mean BDEFS self-regulation of emotions score of 77.0 (SD = 25.2), while the group not reporting stimulant use had a mean score of 63.5 (SD = 29.7, p = .022). Zero-order correlations between SCT and other clinical rating scales differed, as reported in Table 5. SCT was significantly correlated with BDEFS self-organization only for the group taking stimulants. Conversely, SCT correlated significantly with BDI-II, STAI-State and STAI-Trait, and BDEFS-self-regulation of emotion only for the group not taking stimulants.

Table 5.

Zero-Order Correlations (Pearson’s r) Between Independent Variables and BDEFS Subscales.

	Age	ADHD-I	ADHD-HI	BDI-II	STAI-State	STAI-Trait	SCT	BDEFS Time	BDEFS Organization	BDEFS Restraint	BDEFS Motivation	BDEFS Emotion	BDEFS Total EF	BDEFS ADHD Index
Age	1
ADHD-I	.245^† .132	1
ADHD-HI	.033−.044	.408 .401	1
BDI-II	.102−.015	.290* .310*	.223.161	1
STAI-State	.130.056	.289^† .465**	−.078.399**	.487 .742	1
STAI-Trait	.262^† .020	.467 .471	.166.254^†	.572 .695	.690 .845	1
SCT	−.053−.337*	.345* .302*	.216.138	.227.349**	.089.293*	.190.441**	1
BDEFS Time	.311* .207	.085.481**	−.087−.010	.218.179	−.008.136	.281^† .076	.099.135	1
BDEFS Organization	.313* .050	.389** .312*	−.115−.008	.213.226	.260.207	.290^† .206	.427** .263^†	.325* .085	1
BDEFS Restraint	.076−.002	.356* .440**	.606 .553	.253.143	.177.340*	.293^† .261^†	−.015.191	−.018.141	.035.226	1
BDEFS Motivation	.017−.039	.101.362*	.009.101	.374* .123	.054.047	.180.151	.169.126	.189.153	.114.076	.324* .255^†	1
BDEFS Emotion	.070.006	.288^† .408**	.239.473**	.294^† .463**	.285^† .610**	.395* .652**	.216.302*	.295^† −.037	.255^† .357*	.493 .486	.185.103	1
BDEFS Total EF	.262−.095	.197.499**	−.026.337*	.221.376**	.115.337*	.338* .419**	.333* .393**	.727** .285^†	.610 .587	.163.533**	.358* .405**	.559 .548	1
ADHD Index	.393* .106	.187.444**	.006.372*	.315* .170	.196.379*	.329* .358*	.013.271^†	.719** .337*	.342* .047	.308^† .485**	.376* .111	.283.417**	.593** .321*	1

Note. Within each row, the first reported value is for participants taking stimulants (n = 48) and the second value is for participants not taking stimulants (n = 54). Internalizing scales include BDI-II, STAI-State, and STAI-Trait. BDEFS = Barkley Deficits in Executive Functioning Scale; ADHD-I = Conners’ Adult ADHD Rating Scale Subscale E: DSM-IV Inattentive symptoms; ADHD-HI = Conners’ Adult ADHD Rating Scale Subscale F: DSM-IV Hyperactive-Impulsive symptoms; BDI-II = Beck Depression Inventory–II; STAI = State-Trait Anxiety Inventory; SCT = sluggish cognitive tempo; BDEFS = Barkley Deficits in Executive Functioning Scale; BDEFS Time = BDEFS Self-Management to Time; BDEFS Organization = BDEFS Self-Organization/Problem-Solving; BDEFS Emotion = BDEFS Emotional Self-Regulation; EF = executive function.

†

p < .10. *p < .05. ** p < .01.

When the regressions were repeated separately for the groups taking and not taking stimulants, the independent predictive value of SCT symptoms for BDEFS self-organization remained significant only in the group taking stimulants (change in R² = .093, p = .027). In this group, there was also a nonsignificant trend when adding SCT to the model predicting Total EF (change in R² = .110, p = .083). For the group not taking stimulants, none of the BDEFS models improved significantly after adding SCT.

Discussion

The results of this study of SCT in a clinically referred sample of adults with ADHD of a wide age range demonstrate that SCT correlates significantly with ADHD inattentive symptoms, internalizing symptoms, and EF deficits. Our results supported a stronger association between SCT and inattentive symptoms than between SCT and hyperactive-impulsive symptoms, as has been previously described in children (Frick et al., 1994; Lee et al., 2014). However, as in the previous study of adults, the rates of clinical diagnosis of ADHD-I and ADHD-C did not differ significantly between the high SCT and low SCT groups (Barkley, 2012b). Previous studies in children have thus far generally found higher SCT ratings in ADHD-I than in ADHD-C (Garner et al., 2010; Willcutt et al., 2014), but not to a degree sufficient to increase accuracy of subtype identification (Harrington & Waldman, 2010).

Correlations between SCT and dimensional measures of depression and anxiety were significant for the subgroup not receiving stimulants, but rates of mood and anxiety disorders did not significantly differ between participants high and low in SCT. This finding extends to adults the connection between SCT and internalizing symptoms previously observed in children (Becker et al., 2014; Capdevila-Brophy et al., 2014; Garner et al., 2010; Garner et al., 2013; Lee et al., 2014; Willcutt et al., 2014).

Results of hierarchical regression revealed that DSM-IV Inattentive symptomatology was the only variable that contributed to all EF subscales, and was the sole variable that predicted self-management to time. After accounting for inattentive symptoms, DSM-IV Hyperactive-Impulsive symptomatology contributed additional variance to EF subscales related to self-restraint and self-regulation, both of which are associated with poor impulse control. After consideration of ADHD symptoms, internalizing symptoms contributed additional unique variance to self-regulation of emotions, and self-motivation. The characteristics measured by self-regulation of emotion and self-motivation on the BDEFS thus appear to be largely emotionally driven and are more highly associated with internalizing psychopathology than with ADHD-related executive dysfunction.

Given our initial specific aims, the most noteworthy finding to emerge from this study is the significant relationship between SCT and executive dysfunction as measured by the BDEFS self-organization/problem-solving subscale and the total EF summary subscale. Our study replicates the previous findings of a relationship between SCT and deficits in self-organization/problem solving in college students (Jarrett et al., 2017) and the parallel, though weaker, findings in children and adolescents (Barkley, 2013). Organization was also among the EF deficits found to be associated with SCT symptoms by some groups using the BRIEF (Araujo Jiménez et al., 2015; Becker & Langberg, 2014). Importantly, the current study demonstrates the predictive utility of SCT vis-à-vis these indices of executive dysfunction over and above correlations between SCT and ADHD or internalizing symptoms.

Intriguingly, after splitting the sample by reported stimulant use, SCT’s independent predictive value for self-organization/problem solving remained significant only in the group taking stimulants. As this is an observational study without premedication measurements, it is not possible to say whether this is an effect of stimulant use or of other characteristics that differed between those taking versus not taking stimulants. Speculatively, an explanation for this finding could be that by reducing core ADHD Inattentive symptoms (CAARS-E), stimulant use unmasks more specific executive dysfunction, increasing the patient’s awareness and making it more available to the patient for self-rating.

The beta coefficients from the hierarchical regression models also indicate that specific internalizing symptoms had specific associations with different BDEFS subscales. Namely, BDI-II and STAI-State were predictive of self-motivation (STAI-State in the negative direction) and STAI-Trait were predictive of self-regulation of emotions. It is interesting in this context that among the internalizing variables, SCT was primarily correlated with trait anxiety, rather than with depression or with state anxiety. These findings were not directly related to our hypotheses regarding SCT, but nevertheless contribute to a better characterization of specific relationships between BDEFS subscales and non-ADHD symptom scales.

In summary, the current study adds to a growing body of evidence that SCT contributes additional impairment in EF that is not accounted for by comorbid ADHD or internalizing symptoms and that this impairment is primarily in the domain of organization and problem solving. This finding may help to explain the functional impairment in work and education associated with SCT in adults (Barkley, 2012b) as well as the report of a negative association between SCT and quality of life in adults (Combs et al., 2014). Furthermore, it is consistent with our finding in this sample of lower educational attainment in adults with high SCT. This finding needs further replication before firm conclusions can be made regarding any specific relationship between SCT symptoms and educational attainment in adults with ADHD.

Overall, these results demonstrate that SCT in adults is not exclusively a proxy for ADHD symptom severity or internalizing symptomatology. Rather, SCT symptoms predict independent executive functioning impairment above and beyond that predicted by ADHD and internalizing symptoms. Further research will be necessary to ascertain why this result primarily occurs in adults concurrently treated with stimulants.

Limitations of this study include the fact that structured diagnostic interviews were not used to establish diagnoses and that symptoms were measured by self-report. However, the use of CAARS-E symptoms as an inclusion criterion adds validity to the clinical diagnoses. In addition, the results found for this well-educated, treatment-seeking sample may not be fully generalizable to the entire population of adults with ADHD. Conclusions also cannot be generalized to persons without ADHD.

Footnotes

Declaration of Conflicting Interests

The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The author(s) received no financial support for the research, authorship, and/or publication of this article.

Author Biographies

John E. Leikauf, MD, is a child and adolescent psychiatry fellow at Stanford University School of Medicine.

Mary V. Solanto, PhD, was most recently associate professor, Departments of Psychiatry and of child and adolescent psychiatry at New York University School of Medicine.

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