INTRODUCTION
Attention Deficit Hyperactivity Disorder (ADHD), Combined Type, is an
externalizing disorder characterized by inattention, disinhibition,
impulsivity, and excessive motor activity (Goodyear
& Hynd, 1992). These motor symptoms are evident through
developmentally inappropriate levels of fidgetiness, difficulties staying
seated, inappropriate/excessive movement, difficulties waiting
one's turn, and excessive manipulation of objects (Barkley, 1997a). Anecdotal and observational evidence
indicates that children with ADHD have great difficulty restricting their
behavior to conform to instructions/rules and with deferring
gratification/resisting temptation (Barkley,
1997a). In addition to demonstrating higher activity levels, these
children also exhibit qualitatively more inappropriate and intrusive motor
behaviors (Porrino et al., 1983). Hyperactive
children appear less able to inhibit their motor activity when asked to do
so (Ullman et al., 1978), and demonstrate more
off-task behavior, out of seat behaviors, and forbidden “touching of
objects” than non-hyperactive children (Barkley, 1991, 1997a). Given the
above-noted symptoms, some theorists have proposed that ADHD is uniquely
characterized by overactivity and difficulties with motor regulation
(Halperin et al., 1992), with these symptoms
distinguishing ADHD from other psychiatric conditions.
It has been proposed that some of the challenging behaviors seen in
children with ADHD closely resemble those seen in individuals with
documented frontal lobe pathology (Barkley,
1997a; Chelune et al., 1986; Goodyear & Hynd, 1992). Neuropsychological
investigations have supported a “frontal lobe hypothesis” of
ADHD (Barkley, 1997a; Chelune
et al., 1986; Gorenstein & Mammato,
1989; Grodzinsky & Diamond, 1992;
LaPierre et al., 1995; Pennington & Ozonoff, 1996; Shue & Douglas, 1992). In addition, neuroimaging
investigations have identified abnormal metabolism within frontal-lobe
systems in children with ADHD (Sieg et al.,
1995; Zametkin et al., 1990, 1993), and both structural and functional neuroimaging
studies have suggested dysfunction within frontal-striatal systems in
these children (Alexander et al., 1990; Casey et al., 1997; Casey,
2001; Cummings, 1993; Groenewegen et al., 1997; Lou et
al., 1989; Roeltgen & Schneider,
1991; Tannock et al., 1989; Zametkin et al.,
1993) .
Frontal-striatal circuits, including basal ganglial-thalamocortical
pathways running from the prefrontal cortex through the basal ganglia and
thalamic nuclei, have been associated with the voluntary control of motor
activity and the suppression of inappropriate action/behavior (Kroptov & Etlinger, 1999). Statistically
significant correlations between behavioral inhibition and
frontal-striatal volumes have been obtained in children with ADHD (Casey, 2001), suggesting that dysfunction in these
circuits could be associated with the clinical symptomatology of ADHD.
While frontal-striatal networks likely influence many aspects of behavior,
research suggests that they may be particularly important for controlling
attention, inhibition, and motor intentional behavior (Hynd et al., 1991a). Indeed, some authors have
conceptualized ADHD as a disorder specifically of neural systems
subserving the regulation of motor control (Hynd et al., 1991a, 1991b; Niedermeyer & Naidu, 1997; Niedermeyer & Naidu, 1998). Associations between
motor problems and ADHD have been seen in a number of studies (Tannock, 2000), including tests of fine and gross
motor skills (Carte et al., 1996; Kadesjo & Gillberg, 1998), as well on tasks
requiring motor control and coordination (Mariani &
Barkley, 1997; Piek et al., 1999).
Given the prominence of motor regulation problems in the clinical
symptomatology of ADHD and evidence for dysfunction in frontal-striatal
circuits, we investigated the possibility that some of the motor
disinhibition seen in this population could reflect frontal lobe UB; for a
comprehensive review of the “Utilization Behavior” syndrome,
see Archibald et al. (2001). UB is a phenomenon
noted in individuals with dysfunction in frontal brain systems. First
coined by L'hermitte (1983), the term
“Utilization Behavior” refers to a neurobehavioral syndrome
that reflects instrumentally correct, yet highly exaggerated and
inappropriate, motor responses to environmental cues and objects (Eslinger et al., 1991; L'hermitte, 1986). Patients have been described
as automatically using objects in the environment in a manner that is
“object-appropriate,” but that is inappropriate for the
particular context. According to Eslinger (2002), these patients display “unintended and
disinhibited actions that are solely triggered and compelled by objects in
the environment.” Furthermore, they may be unaware or unconcerned
that their actions may be socially inappropriate. For example, a patient
may pick up a toothbrush and begin to brush his teeth, in response to a
toothbrush being placed in front of him, but in a setting in which
brushing one's teeth would not be appropriate, such as in an
appointment with a doctor. In a neuropsychological evaluation, a patient
with UB might automatically pick up a pen and paper and begin writing
something, in a situation where it is inappropriate or the patient has not
been requested to do so. UB has also been described in the context of a
more global “environmental dependency syndrome,” which is
characterized by deficits in personal control of action, and a striking
over-reliance on the external social/physical environmental for
guiding behavior (Eslinger, 2002; L'hermitte, 1986). Most theoretical perspectives
view this syndrome as due to a loss of frontal executive controls
resulting in an imbalance between frontal systems, important for
internally guiding motor activity/behavior, and parietal systems,
important for responding to external or environmentally based stimuli, and
particularly to visual stimuli (Brazzelli et al.,
1994; Eslinger, 2002; Goldberg & Podell, 1995; L'hermitte, 1986; Shallice et
al., 1989). Research has suggested that the pathophysiology of UB
involves dysfunction within frontal-striatal brain systems (Brazzelli et al., 1994; L'hermitte, 1983; L'hermitte, 1986; Shallice et
al., 1989).
Barkley (1997b) was perhaps the first to
propose that children with ADHD might be conceptualized as experiencing
something like UB given their difficulty with the internal control of
behavior and susceptibility to external circumstances. The primary goal of
this study was to determine if ADHD is associated with UB, either as a
part of or in addition to generally heightened activity levels. It was
hypothesized that children with ADHD would specifically
“utilize” objects in their environment versus just explore or
fiddle with objects. Other questions of interest were also explored, based
on the theoretical neurological underpinnings of UB (see Archibald et al., 2001). These included predicting
whether instructions not to touch the objects would influence UB, and
whether UB would occur more during verbal than visual (motor-free) tasks,
more with objects that were familiar versus unfamiliar, and more
in response to objects that were in sight versus those that were
available and known to the child but not visually present.
METHODS
Participants
The sample consisted of two groups of children, recruited from local
elementary schools, ranging from ages 6 to 12 years, matched by age and
gender. Children were initially screened, through a telephone interview
with parents, to determine their appropriateness for inclusion within this
study. The initial screening interview enquired about a history of
attention problems, learning challenges, and other medical/psychiatric
difficulties. Only children who did not have histories of major medical
problems or psychiatric difficulties were selected for more comprehensive
screening for possible inclusion within the study. Participating children
and their parents were compensated with a small monetary stipend.
Inclusion within the ADHD sample was based on two separate diagnostic
indicators: (1) a previous diagnosis of ADHD by a qualified health care
professional (physician or psychologist), and (2) a current diagnosis
based on a structured interview completed by one of the investigators. The
clinical sample consisted of 32 children (28 males and 4 females) all of
whom met Diagnostic and Statistical Manual, 4th Edition (DSM–IV;
American Psychiatric Association, 1994) criteria
for ADHD, Combined Type, based on the Diagnostic Interview for Children
and Adolescents (DICA; Reich et al., 1997) at
the time of the study. Of children that were screened, 15 children were
not included in the final ADHD sample of 32, as they did not meet full
DSM–IV criteria for ADHD, Combined Type, based on the DICA. Children
with ADHD were tested off their stimulant medications, after a washout
period of at least 24 hr.
The control group consisted of 31 children (27 males and 4 females)
without a history of significant developmental, attention, or behavioral
problems. Parents of children in the control sample also completed the
DICA. Children who were included in the control sample had never been
diagnosed with ADHD, and did not meet current diagnostic criteria for
ADHD, based on the DICA. Control participants were matched with children
in the ADHD sample based on age and gender. The demographic
characteristics of each participant group are outlined in Table 1.
Description of ADHD and control samples—demographic
information
Parents of all participants completed the “Child History
Questionnaire,” which requests information about the child's
medical, behavioral, and educational history. The Wechsler Intelligence
Scale for Children Third Edition (WISC–III) Vocabulary Subtest
(Wechsler, 1991) was used to provide an estimate
of verbal intelligence (VIQ). The WISC–III Vocabulary subtest is
known to be a fairly reliable estimate of verbal intelligence as it
correlates well (r = .87) with overall verbal intellectual
ability (VIQ; Wechsler, 1991). The Raven's
Color Matrices Test (Raven, 1947, 1995) was used
as an estimate of (essentially motor-free) nonverbal intelligence (NVIQ;
Spreen & Strauss, 1998). An overall estimate
of intellectual ability was then calculated by averaging the estimates of
IQ obtained from the WISC–III Vocabulary and the Raven's
Colored Matrices. It should be noted that both the WISC–III
Vocabulary and Raven's tests are thought to correlate moderately well
(r = .70 and r = .79, respectively) with estimates of
general intellectual ability (Spreen & Strauss,
1998; Wechsler, 1991). Although some
children utilized objects during administration of cognitive (verbal)
tasks, they were able to answer the questions and the administration was
deemed valid. Groups were found to differ significantly on the estimate of
verbal intellectual abilities, but did not differ on the estimate of
nonverbal intelligence (NVIQ; see Table 1). As a
consequence, the ADHD and control samples did differ significantly in
estimates of overall intellectual ability. However, estimates based on the
average of verbal and nonverbal abilities for both groups fell solidly
within the average range (M ADHD = 64.08 %ile, SD =
19.73; M Control = 76.92 %ile, SD = 14.78). There were
no children with overall estimates of intelligence below a standard score
of 80. Forty-four percent of the ADHD sample had learning difficulties,
versus none of the controls, but ADHD children with learning
difficulties were not excluded due to the high co-morbidity of learning
difficulties with ADHD.
Procedures
All children were tested individually at the University of Victoria.
The testing room was set up to give children easy access to objects. To
determine if the child's behavior was influenced by the “visual
pull” of objects, objects were placed both within and outside of the
child's line of sight, although all were easily within their reach.
For this purpose a special table was designed, with an “opening
top” similar to a child's school desk, with an 8-inch high
opening in the front by 36-inches wide, allowing access to a shelf (made
of a glass for videotaping from below). This was constructed to allow
children access to objects “in the desk,” which they could
easily touch but that were not visible. At the start of each session, as
children entered the testing room, the table was “open” so
that children were able to look at the objects inside the table. Once the
child was seated, the “opening top” of the testing table was
closed, though the objects were clearly within reach through the large
opening in front. Objects were just above hand level for children seated
with hands in their laps.
To investigate if instruction set/expectation influenced the
children's behavior, half of the sample was randomly assigned to an
“instruction condition” and asked at the beginning of the test
session not to touch any of the objects in or around the table. The other
half of the sample was not given any instructions or directions regarding
the objects. This was the only discussion of the “objects”
that occurred during the testing session.
To see if object familiarity influenced children's behavior,
objects that should have been “familiar” to or commonly used
by children (e.g., scissors, stapler, stopwatch, small telescope, cup,
brush) and items that were “unfamiliar” or rarely used by most
children (e.g., garlic press, wood working tool, clamp, wood planer (blade
removed), wine bottle vacuum, ear syringe, table lamp clamp) were
selected. Objects were placed in one of two locations, inside the table or
on the top right-hand side of the table with an equal number of familiar
and unfamiliar objects either clearly visible (i.e., on top of the table)
or out of sight (i.e., inside the closed testing table). Objects were
positioned in exactly the same location for all participants.
Each session was videotaped using two VHS cameras. The first camera
was mounted high on a wall opposite the testing table and positioned
facing the child, to record behaviors above the table. The second camera
was located underneath the testing table and was angled upwards through
the plate glass shelf of the table. This gave a clear view if a child put
his or her hand(s) inside the table and touched or manipulated any of the
objects inside the table (out of the child's view).
While sitting at the testing table, all children were administered the
WISC–III Vocabulary subtest (Wechsler,
1991) and the Raven's Colored Progressive Matrices test (Raven, 1947, 1995), to compare levels of motor
behavior during verbal versus visual (motor-free) tasks. All
children also participated in an “unsupervised activity”
within the same room. During this activity, participants were left on
their own with instructions to complete, in 10 min, as many simple math
problem sheets as possible.
Behavioral observations were the primary means of evaluating motor
behaviors. Instances of object-directed behaviors (defined as touching of
objects) were coded using Shallice's categorization and coding scheme
(1989), when there was “use of one or more
objects lasting more than 1 s, following the end of a previous instance of
object use by at least 1 s.” As per Shallice's coding scheme
object-directed behaviors were categorized as either: “True
Utilization Behavior,” “Complex Toying,” or
“Toying.”
True Utilization Behavior was defined as “a set of actions
integrated in a typical fashion with respect to the relevant
object(s).” Complex Toying was defined as “the use of two
objects in a linked way, but in an incomplete fashion or not for the
purpose for which both objects were designed,” or
“the use of an object in a purposeful way but not for its
intended purpose.”
Toying was operationally defined as “a single action in which an
object is manipulated but not in any purposeful way or for its intended
use.” Instances of simple Toying, in which children merely fiddled
with objects, were not considered examples of UB as children did not
“utilize” the objects in any purposeful way.
Observations of object-directed behaviors of the participants
indicated that Complex Toying was typically purposeful in relation to
objects, and that it generally occurred when children were not familiar
with the exact function of an object. In this case, children utilized the
object in a manner that would be appropriate for a similar object with
which they were familiar (e.g., using the ear syringe as if it were a pump
or the table clamp as if it were a paper clip). As Complex Toying and True
UB both involved purposeful manipulation of objects (i.e., children seemed
to utilize objects “appropriately” for what they thought the
purpose was), these two categories were considered examples of UB. They
were therefore combined to yield a score called “Total UB,” in
keeping with the coding scheme developed by Shallice et al. (1989).
To assess general motor activity, instances of self-directed motor
behaviors (Self-touching) were also recorded to rule out a general
“activity level” confound. Self-touching was operationalized
as “any behavior in which a child touches his/her upper body,
face area, or clothing for more than 1 s following the end of a previous
instance of Self-touching by at least 1 s.” Occurrences of resting
one's head in one's hands and/or fidgeting with one's
fingers were not considered examples of Self-touching.
Object-directed (Toying, Complex Toying, and True Utilization
Behavior) and self-directed (Self-touching) movements were counted over
the duration of the testing session, which was the same for all
participants. In this study, total behavior counts were recorded by
tallying the number of object-directed (in response to each object) and
self-directed motor behaviors over different activities.
Intraclass correlation coefficients, to assess reliability of
behavioral coding, were obtained on a portion of the sample (20%).
Inter-rater reliability coefficients ranged from .87 to .97 across the
four behaviors of interest (see Table 2).
Inter-rater reliability coefficients
RESULTS
Analyses of Behavior
Intellectual ability was not statistically related to any of the
measures, and therefore was not used as a covariate in the analyses.
To explore the nature of motor behaviors observed within the testing
situation, behavioral ratings of Self-touching, Toying, Complex Toying,
and True UB were analyzed using a MANOVA with four behaviors as the
within-subjects factor and one between-subjects factor (group). Analyses
revealed a statistically significant interaction between the motor
behaviors and group membership (Greenhouse-Geisser corrected
F(3,180) = 3.38, p = .039) and a significant effect of
behaviors (Greenhouse-Geisser corrected F(3,180) = 28.16,
p < .001). See Figure 1. Further
analysis of this interaction using Bonferroni corrected post-hoc
tests revealed no significant differences between the groups on the
Self-touching behaviors (M ADHD = 47.5, SD = 25.94; M
Controls = 38.73, SD = 26.89; t(1,61) = 1.31, p
= .197). Group differences in Toying behavior were marginally significant
(M ADHD = 17.9, SD = 37.92; M Controls = .35,
SD = .61; t(1,61) = 2.47, p = .016). The groups
differed significantly on both Complex toying (M ADHD = 12.84,
SD = 21.45; M Controls = .06, SD = .25;
t(1,61) = 3.32, p = .002) and on True UB (M
ADHD = 35.38, SD = 49.82; M Controls = .26, SD
= 1.44; t(1,61) = 3.92, p < .001) Indeed only two
subjects from the control sample exhibited any object-directed motor
behaviors, one with eight instances of UB, and the other with one instance
of Toying.
Comparison of motor behaviors in ADHD and control participants. Using
Bonferroni corrections for multiple comparisons; *p < .05;
**p < .01; ***p < .001. Error bars are standard
errors.
Given that the group differences in Complex Toying and in True UB were
both highly significant and that both of these behaviors reflected
purposeful use of at least one object in an “appropriate”
manner, we used the Total UB score (Complex Toying plus True UB) for all
further analyses. In addition, given the exceptionally low frequency in
the control group of any behavior that was scored as UB, investigations
into other dimensions of behaviors coded as UB were conducted using data
from the ADHD sample only.
Results of a within-subjects paired t-test revealed that
children with ADHD demonstrated significantly higher levels of Total UB
(M = 48.22, SD = 63.06) than mere Toying (Toying;
M = 17.19, SD = 37.92; t(31) = 3.05, p
< .01). Total UB was significantly higher in response to objects that
were familiar (M = 42.41, SD = 56.81) versus
those that were unfamiliar (M = 5.81, SD = 10.28,
t(31) = 3.99, p < .001; see Figure
2). Children with ADHD were much more likely to utilize objects
that were within their line of sight (M = 46.03, SD =
61.22) compared with those that were out of sight (i.e., inside the
testing table; M = 2.19, SD = 5.56, t(31) =
4.14, p < .001; see Figure 2).
Finally, Total UB was significantly more frequent during the verbal task
(Vocabulary) than during the motor-free visual task (Raven) (M
Vocab = 15.78, SD = 22.50; M Ravens = 2.16, SD
= 8.49; t(1,31) = 3.30, p = .002; see Figure 2).
Comparison of utilization behaviors in the ADHD group across
conditions; **p < .01, ***p < .001. Error bars are
standard errors.
To address concerns that object utilization may be a result of the
children's misunderstanding the purpose of or “rules”
with respect to objects placed in and around the testing table, levels of
Total UB were compared under incidental (no instructions) and
instructional (including a statement “not to touch” objects)
conditions. Using independent samples t-tests, results indicated
that equivalent levels of Total UB occurred when children were given
instructions not to touch the objects as when they were not given any
instructions regarding the objects (M No Instruction = 35.57,
SD = 52.57; M Instruction = 58.06, SD = 70.02;
t(1,31) = 1.00, p = .325).
To better capture variability of UB within the ADHD group, we
characterized children as “Utilizers” or
“Non-Utilizers” using a cut-off criteria. Children in the ADHD
sample who had a Total UB score of greater than 18 (more than twice that
of the highest control subject) were categorized as
“Utilizers.” Using this scheme, 53.1% of the ADHD sample was
so characterized, though considerable variability in the frequency of this
behavior was noted even in children who did exhibit it. There were no
differences between the Utilizers and the Non-Utilizers on a number of key
variables including age, Vocabulary, Raven's, having a diagnosis of
learning disability, or inclusion in a special behavioral classroom (see
Table 3).
Comparison of ADHD “Utilizers” and
“Non-Utilizers” on key variables
To explore the relation between UB and severity of ADHD
symptomatology, Pearson correlations were obtained between Total UB and
numbers of hyperactive and inattentive symptoms reported by parents on the
DICA. Total UB was significantly correlated with number of hyperactive
symptoms as reported on the DICA [r(30) =.45, p =
.014], but not with number of inattentive symptoms
[r(30) =.12, p = .583].
DISCUSSION
The goal of this study was to identify whether some of the
inappropriate/excessive motor activity seen in children with ADHD
could be characterized as UB, either as a part of or in addition to
generally heightened activity levels. The literature suggests that
children with ADHD have difficulty with self-regulation, may be less
controlled by internally represented information, may be more influenced
by external circumstances (Barkley, 1997b), and
may manifest dysfunction in frontal-striatal systems (Casey et al., 1997).
Results indicated that children with ADHD showed significantly higher
levels of Complex Toying and True UB (Total UB), and marginally
significantly more Toying behaviors than did non-ADHD children. In
contrast, the children with ADHD and the non-ADHD children did not differ
on Self-touching behavior. These findings suggest that children with ADHD
are much more likely to reach out and “use” objects in their
environment than are non-ADHD children. Indeed, with the exception of one
participant, children within the control sample did not engage in any
complex toying or True UB, while using a control-referenced criteria,
whereas approximately 53% of the ADHD sample demonstrated UB. On informal
observations during testing, these children also presented as considerably
more active and dysregulated than other children diagnosed with ADHD who
did not display UB. Consistent with these informal observations, levels of
UB within the ADHD sample were significantly and specifically correlated
with the severity of hyperactivity, but not inattention, as reported by
parents on the DICA.
Examination of these UB behaviors within the ADHD sample revealed that
these children were much more likely to truly “utilize”
objects than to fiddle aimlessly with them, or even to engage in Complex
Toying. This suggests that children with ADHD may be displaying behavior
consistent with True UB rather than just simply fidgeting as a result of
generally heightened activity levels. Further corroboration of this was
provided by the finding that children with ADHD did not demonstrate
significantly higher levels of Self-touching behaviors than did non-ADHD
children. Again, this argues against the suggestion that children with
ADHD touch more objects simply because they are generally more active and
tend to touch everything around them. Furthermore, higher levels of UB in
this population did not appear to be simply due to more uncooperative
behaviors or an “implicit” expectation that objects
“should be” used, as has been a concern in previous studies
(Shallice et al., 1989). A comparison of an
“instruction condition” (in which instructions not to use the
objects were provided) and a “no instruction condition”
indicated that instructional set or expectation did not significantly
influence the levels of UB.
Results also indicated that UB was more common in response to objects
that were familiar versus those that were unfamiliar, again
supporting the contention that this behavior is not simply due to
generally heightened activity levels towards all aspects of the
environment. This finding also provides support for theories suggesting
that UB may result from disinhibition/release of preprogrammed
parietal/lateral motor schemata, as a result of dysfunction within
frontal control systems (Archibald et al., 2001;
Shallice et al., 1989). If UB results from a
release of familiar or “preprogrammed” action schemata, one
would expect to see UB in response to objects that are familiar (for which
an individual has developed a schemata), but not in response to unfamiliar
objects.
Finally, some individuals have suggested that UB may result from an
imbalance between a medial and lateral motor system that would result in
high levels of visually driven behavior (Goldberg,
1985). The results of this study provided some support for this
contention in that, first, UB within the ADHD sample occurred much more
often in response to objects that were in sight (on the table), compared
with those that were out of sight (inside the table). These results
suggest that UB could be triggered and compelled by objects in the
environment, possibly due to a release of lateral motor systems that are
associated with an organism's responsiveness to the environment
(Archibald et al., 2001; Eslinger, 2002). Again this supports a strong visual
component to UB, as utilization of objects out of the field of vision
would require some mental representation and theoretically invoke the
medial system. Second, utilization behavior was more likely to occur
during a verbal activity than during visual (though motor-free) activity
when the lateral system was likely otherwise engaged in the task.
Disinhibition of the lateral system is less likely when the visual system
is occupied (Goldberg, 1985), as has been
demonstrated in earlier studies of the UB Syndrome (Shallice et al., 1989). Further investigations of the
association between behaviors classified as UB and performance on motor
measures, which specifically assess functioning of the respective
“lateral and medial” motor systems, would be useful in
clarifying theoretical frameworks for UB.
In sum, the present study provided evidence that some of the
inappropriate and excessive motor behavior in children with ADHD may be
associated with UB. Our results are consistent with theorists such as
Barkley (1997b) who has proposed that children
with ADHD may be less well controlled by internally represented
information and more so by external stimuli. These results are also
consistent with studies suggesting a frontal-striatal basis for ADHD;
evidence for UB provides additional support for a disruption of frontal
motor connections in ADHD, leading to difficulties with motor control
(Niedermeyer & Naidu, 1997) within this
population. Our results are consistent with previous studies documenting
impaired “frontal motor abilities” in children with ADHD
(Grodzinsky & Diamond, 1992; Shue & Douglas, 1992) and with recent neuroimaging
data suggesting that ADHD may result from frontal-motor uncoupling as a
result of dysfunction within frontal-striatal circuits (Casey, 2001; Casey et al.,
1997; Hynd et al., 1991a; Niedermeyer & Naidu, 1997).
It is also important to consider the clinical relevance of some of
these findings. Excessive touching of objects in the environment is a
frequent complaint of parents of children with ADHD, and is typically seen
as “non-compliant” behavior. Given that some of the intrusive
and inappropriate motor behavior seen in children with ADHD (particularly
the excessive utilization of objects in the environment) could be
conceptualized as due to UB, at least some of the challenging behaviors
seen in this population may not be “motivationally” based. The
association between hyperactivity and UB should be further investigated in
future studies, as this could have implications for
treatment/management of ADHD. In addition, further investigation of
the difference between children with ADHD who demonstrate UB
versus those who do not is clearly warranted. From a clinical
perspective, it is important to recognize that not all children with the
diagnosis of ADHD demonstrate UB, and even within those that did, there
was substantial variability in the frequency of this behavior within this
experimental setting. Clearly a significant portion of motor overactivity
in children with ADHD cannot be accounted for as UB and caution should be
exercised when labeling such behaviors.
One clear limitation of this study was the failure to rule out
co-morbid diagnoses, which may also be associated with UB. In the current
investigation, UB in ADHD appeared to be associated with the severity of
hyperactivity and the presence of oppositional and defiant behaviors.
However, it was not possible to determine whether children with
“pure” Oppositional Defiant Disorder (not co-occurring with
ADHD) also exhibit UB, or whether symptoms of ADHD, oppositional
behaviors, and UB, constitute a distinct and more severe subtype of ADHD.
Therefore, this study was not able to determine whether findings of UB in
children with ADHD are indeed specific to this population. Future studies
should investigate UB in children with “pure” ADHD, where
other co-morbid conditions are carefully screened out, and in children
with other disruptive behavior disorders (Oppositional Defiant Disorder,
Conduct Disorder).
