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Attention Deficit Hyperactivity Disorder and the Frontal Lobe Syndrome KAREN

L. SHUE AND VIRGINIA I. McGill

DOUGLAS

University

The usefulness of frontal lobe (FL) dysfunction as a conceptual model for Attention Deficit Hyperactivity Disorder (ADHD) was investigated. Twenty-four ADHD and 24 normal control (NC) children were tested using two batteries of tasks. The first was sensitive to FL deficits in motor control and problem solving skills. The second consisted of memory tasks sensitive to temporal lobe dysfunction. ADHD children differed significantly from NCs on measures of FL function, but not on tests of temporal lobe functions. Where norms were available for normal children on the same FL tests, ADHDs performed like 6- to 7-year-olds, despite their mean age of 10 years and minimum age of 8 years. The differential performance of ADHDs on tasks sensitive to FL and temporal lobe dysfunction supports the hypothesis that ADHD deficits are analogous to FL dysfunction and demonstrates that the children’s deficits do not reflect generalized cognitive im0 IYY2 Academic Press. Inc pairment.

Attention Deficit Hyperactivity Disorder (ADHD) is one of the most frequently diagnosed behavior problems in the pediatric population. The major symptoms are attentional deficits, impulsivity, and excessive activity levels (Diagnostic and Statistical Manual III-R, American Psychiatric Association, 1987). Several authors have pointed to striking parallels between the behaviors of ADHD children and those of adults with frontal lobe damage (Gualtieri & Hicks, 1985; Mattes, 1980; Pontius, 1973; Stamm & Kreder, 1979). More recently, a few investigators have administered tests associated with frontal lobe (FL) dysfunction to ADHD samples (Boucugnani & Jones, 1989; Chelune, Ferguson, Koon, & Dickey, 1986; Gorenstein, Mammato, & Sandy, 1989). The tests were chosen to focus Address correspondence and reprint requests to Karen L. Shue, Ph.D., C. Psych., Repatriation Community Programs, Chedoke Hospital (Patterson Bldg.), Chedoke-McMaster Hospitals, Box 2000, Hamilton, Ontario, Canada LSN 325. This research was supported by Medical Research Council of Canada Grant MA6913 to V. I. Douglas and by a Medical Research Council of Canada Studentship to K. L. Shue. 104 0278-2626192 $5.00 Copyright 0 1992 by Academic Press. Inc. All rights of reproduction in any form reserved.

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on deficits typically associated with FL dysfunction: cognitive flexibility, problem solving, and distractibility. Chelune et al. (1986) compared the performance of ADHD and normal control (NC) children on the Wisconsin Card Sorting Test (WCST). Their battery also included measures of sequential processing and cognitive flexibility, which they consider central to FL dysfunction. On the WCST, they found significant ADHD-NC differences on three of four measures, including categories achieved, perseverative errors, and percentage of correct responses; the groups did not differ on number of failures to maintain set. Chelune et al. did not report results for nonperseverative errors. Findings from the sequential processing tasks did not show a clear pattern. On the cognitive flexibility measures, ADHDs made more errors than NCs on only one, the Color-Forms Test, and the two groups did not differ on time measures on either task. In interpreting their findings, Chelune et al. emphasized the high incidence of perseverative errors made by the ADHD group on the WCST. They suggested that their results pointed to an underlying dysfunction of the inhibitory forebrain system. Gorenstein et al. (1989) selected a group of Inattentive-Overactive (IO) children on the basis of teachers’ ratings on criteria which closely resembled those for ADHD. They compared this group with a NC group on a battery of six tests. Three of their tests, the WCST, the Necker Cube illusion, and the Sequential Matching Memory Test, had previously shown deficits in FL patients. The remaining tests were chosen to assess susceptibility of cognitive processesto competing responses, by comparing baseline and “disruption” trials. These included the Trail-Making Test (TM: Parts A and B), the Stroop Color-Word Test, and the Sequential Memory Test for Children, which was developed by Gorenstein et al. On the WCST, the I-O group made more perseverative errors. Group differences were not found on nonperseverative errors or on total categories achieved. There was also a significant difference between groups on the Sequential Matching Memory Test and a near-significant difference on Necker reversals. The I-O group generally performed more poorly on both baseline and disruption trials on the three tasks that incorporated baseline and disruption measures. Further statistical analyses established that the performance of the I-O group on disruption trials was significantly worse than that of controls, even with baseline performance taken into account. Gorenstein et al. used these results to argue for a prefrontaltype deficit involving “a diminished ability to sustain cognitive activity in the face of competing responses.” This interpretation, however, does not account for the differences found on baseline trials. Boucugnani and Jones (1989) compared ADHD and control groups on the WCST, TM-B, Stroop, and two WISC-R subtests. They reported significant ADHD-normal differences on four measures from the WCST, including perseverative responses, perseverative errors, categories com-

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pleted, and percentage of correct responses. These investigators did not report findings on nonperseverative errors. The ADHD group also performed more poorly than controls on the time measure of TM-B and made fewer correct responses on the Color-Word (distraction) card of the Stroop. Findings were not reported for baseline measures of either of these tasks. Boucugnani and Jones interpreted their results as reflecting problems with perseveration, disinhibition, and attention, as well as the more complex skills involved in response planning, organization, and follow-through. They argued that their results supported a frontal lobe dysfunction hypothesis of ADHD. The studies to be reported further explored possible parallels between ADHD and frontal lobe dysfunction. We were particularly interested in establishing whether deficits shown by ADHD children on frontal lobe tests reflect a specific neuropsychological performance pattern associated with frontal lobe dysfunction, or whether they merely reflect part of a more generalized dysfunctional pattern. To pursue this question, we chose two types of measures. The first was a battery of tasks previously shown to be sensitive to diverse aspects of frontal lobe dysfunction. The second was a battery of relatively simple memory measures on which FL patients typically do not show deficits, but patients with temporal lobe dysfunction perform poorly. The first study included four measures of motor control and two measures of complex problem solving skills. A Go-No Go (GNG) task was used to assesssimple motor inhibition. Drewe (1975), and Guitton, Buchtel, and Douglas (1982) have reported that FL patients are unable to suppress responding to a “no go” stimulus. There is also evidence that ADHD children show difficulties inhibiting responses on more complex tasks with similar response requirements such as the Continuous Performance Test, Delayed Reaction Time tasks, etc. (e.g., Hoy, Weiss, Minde, & Cohen, 1978; Douglas & Peters, 1979; Neuchterlein, 1983). In addition, Trommer, Hoeppner, Lorber, and Armstrong (1988) tested ADHD children on a GNG task with an interstimulus interval (ISI) of 3 sec. They reported that, in contrast to NC and ADD children without hyperactivity, ADHD children did not improve their performance across trials; omission errors actually increased across trials in the ADHD group. A decrement in performance over time has sometimes been reported in ADHD children on attentional tasks (for a review, see Douglas & Peters, 1979). It is possible that the relatively long ISIS used by Trommer et al. may have heightened demands on sustained attentional performance rather than impulse control. Thus, we used briefer ISIS (1 set) to increase task demands for inhibitory control. Our motor measures also included a Conflicting Motor Response Test (CM; Luria, 1973) and an Incompatible Conditional Discrimination (ICD; Drewe, 1975) task. Luria (1973) and Drewe (1975) found that when FL

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patients were asked to perform motor responses opposite to those modeled by an examiner, they tended to respond echopraxically, imitating the model despite their ability to retain and repeat task instructions correctly. FL patients were not impaired on tasks requiring direct imitation. ADHD children have not been tested on tasks of this type. Our final motor control measure was the Trail-Making Test. Reitan (1964) reported that FL patients showed no difference from NC or non-FL brain-damaged subjects on time taken to complete TM-A, but took longer than both control groups to complete TM-B. We tested our subjects on both TM-A and TM-B. Previous investigators have reported that ADHDs show significantly poorer performance on the TM and related tests as assessedby time and error measures (Clarkson & Hayden, 1971; Gorenstein et al., 1989; Homatidis & Konstantareous, 1981). To assess higher level problem solving abilities, we used the WCST and the Self-Ordered Pointing (SOP) task (Petrides & Milner, 1982). Petrides and Milner developed the SOP to assessresponse organization and planning. They found that FL patients showed deficits, while patients with damage restricted to other cortical areas did not. On the WCST, we scored both perseverative and nonperseverative errors. We considered the nonperseverative measure to be important because some theorists have emphasized the failure of FL patients on the problem solving aspects of the WCST and related tasks, as opposed to “perseverative” responding per se (e.g., Pribram, 1973; Shallice, 1982; Petrides, 1989). Although Gorenstein et al. (1989) interpreted their finding that I-O children made more perseverative, but not more nonperseverative, errors than controls as evidence of a pattern similar to that seen in FL patients, some researchers have reported more errors of both kinds in FL patients (Drewe, 1974; Robinson, Heaton, Lahman, & Stilson, 1980). As in the ADHD studies reviewed, other investigators have failed to report data on nonperseverative errors in their FL groups (Cavazutti, Fischer, Welch, Belli, & Winston, 1983; Milner, 1963, 1964). Several recent investigators have examined developmental changes in behaviors attributed to frontal lobe functioning. Using normal children ages 6 to 12 years, Chelune and Baer (1986), Passler, Isaac, and Hynd (1985), and Becker, Isaac, and Hynd (1988) found different developmental patterns on different FL tasks. In contrast to motor control skills, in which normal children consistently showed optimal performance levels by 6 to 7 years, cognitive problem solving skills showed major developmental changes between 10 to 12 years. Efficiency and quality of strategies used on these tasks improved gradually. Moreover, the performance of children younger than 8 years resembled findings from studies of FL patients (Becker et al., 1988; Chelune & Baer, 1986; Eimas, 1970; Kagan et al,, 1979; Passler et al., 1985). Chelune et al. (1986) addressed the issue of developmental changes in

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ADD children on the WCST. They reported that their ADD group made appropriate gains, but at a level approximately 2 years behind their agematched cohorts. Boucugnani and Jones (1989) also suggested that differences between their ADHD and NC groups could be explained by a developmental lag hypothesis. Thus, we were interested in evaluating the developmental level of our group in the context of available normative data. STUDY 1

The purpose of Study 1 was to compare the performances of ADHD and normal children on a battery of motor control and problem solving tasks on which FL patients have shown performance deficits. Method Subjects The samples included 24 ADHD children (21 males, 3 females) and 24 NC children aged 8 to 12 years. Groups were matched on sex, receptive vocabulary IQ Peabody Picture Vocabulary Test (PPVT), and age. Informed consent was obtained from all children and their parents.

Selection Criteria and Procedures ADHD subjects. Each ADHD child had been referred to the Hyperactivity Project at the Montreal Children’s Hospital for attentional and impulsivity problems. To be included in the study, children had to meet the DSM-III diagnostic criteria for ADDH and DSMIIIR criteria for ADHD. In addition, they had to receive ratings of 1.5 or greater on the Hyperactivity Index of both the Revised Conner’s Teacher Rating Scale (TRS) and Parent Rating Scale (PRS; Goyette, Connors, & Ulrich, 1978). Interviews with the mothers established that the children’s problems were chronic and pervasive. In addition, the symptoms could not be attributed to demonstrated brain damage, epilepsy, psychosis, or anxiety. Subject’s IQs had to be above 80 as measured by the PPVT. All children receiving stimulant medication (N = 9) had not been medicated for at least 20 hr before testing. Normal controls. Normal control subjects were recruited from the same school as the ADHDs and were matched on sex, age (within 6 months), and IQ, but did not show behavioral or emotional difficulties. Parents of potential control children were contacted by telephone and a short interview was carried out to verify that the child did not show attention, impulse control, or activity problems and did not have a history of emotional difficulties, brain damage, epilepsy, or psychosis. None of the children were taking psychotropic medication. Scores on both the PRS and TRS had to be below 1.5 on the Hyperactivity Index of the scale. Means and standard deviations for the ADHD and NC groups on age, IQ, TRS and PRS ratings are shown in Table 1. T tests showed no significant differences between ADHD and NC groups in age or IQ. As expected, the ADHD children received significantly worse ratings than the NC children on the TRS, f(46) = 18.20, p < .OOOl, and the PRS, t(46) = 13.21, p < .OOOl.

General Procedure Subjects were tested individually in their schools in a single session lasting approximately 1 hr. Tests were administered in one of three orders. Orders were randomly determined

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TABLE 1 DEMOGRAPHICCHARACTERISTICSOF ADHD AND NORMAL CONTROL GROUPS (MEANS AND STANDARD DEVIATIONS) Group

Age (months)

IQ

TRS

PRS

ADHD

123.54

96.42

2.27*

2.12*

(N = 24)

[ 18.823

[ 10.931

[ .40]

1.431

;:

123.71 [ 18.481

96.88 [11.57]

0.3 [.35]

0.56 [.39]

= 24)

Nore. TRS, Teacher rating scale; PRS, Parent rating scale. * p < .OOOl.

with the restriction that tests involving similar materials did not immediately follow one another. In addition, order of administration of the Compatible and Incompatible Conditional Discrimination (CCD; ICD) tasks was counterbalanced.

Test Materials and Administration Go-No Go task. This task requires rapid discrimination of “go” (S +) and iino go” (S-) signals. Stimuli included 40 cards with pictures of an apple (S + ; 20 cards) or ice cream cone (S - ; 20 cards). Subjects were required to press a response key as quickly as possible when presented with the S + , but to refrain from pressing in response to the S - Based on Trommer et al.‘s (1988) results and those of a pilot study, very brief (I XC) interstimulus intervals were used in order to increase task demands. Responses to the S- were scored as errors. Conflicting Motor Response Tess (Adapted from the Luria-Christensen battery; Christensen, 1975). Subjects were told: “If I show you my finger. you show me your fist. If I show you my fist, you show me your finger.” The two gestures were presented 40 times at a rate of one gesture per second. Echopraxic errors were recorded. Compatible and Incompatible Conditional Discrimination tasks. Stimuli included 20 blue and pink cards. The examiner presented the cards at a rate of one card per second. In CCD, subjects were asked to name and point to a response card which was the same color as the stimulus card. In ICD, subjects were asked to name and point to the differently colored card. On both tasks. they were required to name the color of the card to which they pointed. Order of administration of CCD and ICD was counterbalanced. Verbal and motor errors were scored. Trail-Making Test-Forms A and B. In TM-A, subjects are required to sequentially connect randomly placed numbers as quickly as possible. In TM-B, subjects must alternately connect sequential numbers and letters as quickly as possible. The adult version was administered, using standardized instructions (Reitan, 1986). Time taken for correct completion and number of errors were recorded. Wisconsin Card Sorting Test. The standard method of administration and scoring was used (Heaton, 1981). Five measures of performance were recorded: (1) number of categories achieved (O-6); (2) “extra correct” responses: number of cards correctly sorted, but not a part of the 10 consecutive correct responses; (3) perseverativc errors: errors which would have been correct for the previous category; (4) nonperseverative errors: any incorrect placement not of a perseverative nature; and (5) unique errors: those not matching the card with which they were paired in color, form, or number. Self-Ordered Pointing task. Subjects were presented with stacks of 21.5 x 2%cm pages on which matrices of 6, 8, IO. or 12 representational pictures or abstract designs were drawn.

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TABLE 2 MEANSAND STANDARDDEVIATIONSOFADHD AND NORMALCONTROLGROUPSON MOTOR CONTROLMEASURES ADHD Go-No Go task Errors Conflicting Motor Response Test Errors

2.75

c.01

4.83 [2.60]

2.04 [1.78]

4.34

.05. T tests on the mean number of digits recalled forward and backward yielded no differences on either of the Digit Span measures (DS-F: t(38) = .20, p > .05; DS-B: t(38) = 1.28, p > .05). WMS: Delayed recall of LM and PA. T tests, computed for recall of the LM stories and PA lists following the 30-min delay, yielded no significant differences between the groups for either dependent variable. However, a trend on the delayed recall of PA, F(1, 38) = 3.74, p < .06, reflected somewhat higher recall in the NC group (NC mean = 9.67; ADHD mean = 8.95 of 10). Location Recall task. T tests revealed no group differences on either the number of objects recalled immediately after viewing the array, t(38) = 1.51, p > .05, or on the average displacement of objects from their positions in the original array, t(38) = 1.00, p > .05. Using the method of Smith and Milner (1981, 1984) to assessdifferences in price estimation, a cutoff point was set at + 2 standard deviations from the mean of the price estimates given by the NC children for each object. Estimates falling outside this range were considered errors. Twenty children in the ADHD group made a total of 74 errors; while seven NC children made a total of 15 errors. x2 analysis indicated a significant difference in the number of subjects making errors (x2 = 4.68, p < .05).

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SYNDROME

TABLE 4 MEANS AND STANDARD DEVIATIONS OF ADHD AND NORMAI. CONTROL GROUPS ON MEMORY TASKS

Wechsler Memory Scale: Logical Memory Immediate recall Delayed

recall

WMS: Logical Memory Immediate recall Delayed

NC

t/F

P

story A 7.43 [3.35] 6.11 [2.76]

7.17 [3.31] 5.67 2.4')

0.24

n.s.

0.36

n.s.

7.30 [3.19] 6.48 [3.50]

6.78 [3.10] 6.33 [3.35]

0.52

n.s.

0.17

n.s.

15.OY [2.81] 8.95 (1.291

15.92 [2.88] 9.67

0.91

n.s.

3.74

< .06

5.41 [ 1. IO] 4.18 [.X0]

5.33 (I.331 3.83

0.20

n.s.

I.28

n.s.

8.77 [1.50] 5.Y2 [.5X] 3.42

Y.67 [2.25] 5.38 l.701 0.83

1.51

ns.

I .ClO

n.s.

story B

recall

WMS: Paired Associates Immediate recall Delayed recall WMS: Digit Span Forward Backward Location Recall task No. of objects recalled Mean object displacement Mean estimation

ADHD

errors

(cm)

I.971

I.921

4.15

c.001

A t test yielded a significant difference between the groups in the mean number of errors made, t = 4.15, p < .OOl. Discussion of Study 2 As predicted, the performance of ADHDs did not differ significantly from NCs on any of the WMS recall measures. Although ADHDs obtained slightly lower scores on delayed recall of PA word pairs, the difference did not reach significance. PA tasks on which ADHD-NC differences have been reported have contained more items and significant ADHDNC differences occurred only on arbitrarily paired items (Douglas & Benezra, 1990). These results are consistent with other findings suggesting that ADHD subjects can perform at normal levels on tests which do not require the use of complex mnemonic strategies (Benezra & Douglas,

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1988; Douglas & Peters, 1979). It is noteworthy, however, that, like FL patients (Luria, 1973; Stuss & Benson, 1984), ADHD children have difficulty with more complex memory measures which require the generation of organizational strategies (August, 1987; Douglas & Benezra, 1990). The dissociation between recall performance and price estimation shown by ADHD children also resembles findings from FL samples (Smith & Milner, 1984). ADHDs and NCs did not differ on accuracy of object recall or object location. In contrast, like FL patients, ADHDs gave significantly more extreme price estimates. In addition, the mean number of extreme estimates made by our subjects closely resembles the number reported for right FL (RF) and NC adults by Smith and Milner (1984). Smith and Milner’s RF patients made an average of 3.7 extreme price estimates, while our ADHDs made 3.4. Adults in their normal control group made 0.6 extreme estimates compared to 0.8 for our normal children. Thus, the performance of our ADHD children closely resembled that of FL patients. Insofar as estimation tasks assessconceptualization and planning strategies (Shallice, 1982; Smith & Milner, 1984), these results are consistent with findings from our problem solving tasks in Study 1. GENERAL DISCUSSION Comparison with FL Dysfunction

Results from Studies 1 and 2 support the hypothesized parallels between ADHD and FL dysfunction. ADHD children consistently performed poorly on a variety of measures sensitive to FL dysfunction. More importantly, their impairments appear to be relatively specific to FL processes. On tasks sensitive to FL and temporal lobe function, ADHD children showed the same pattern of difficulties and intact functions reported by other investigators for FL patients. They were impaired on tests measuring frontal lobe functions, but did not differ from NC children on tests sensitive to temporal lobe function. The Location test provides a particularly good example of this dissociation. Like Smith and Milner’s (1984) FL patients, ADHD children made extreme estimates of the prices of stimulus objects. Also like the FL patients, ADHD children showed normal immediate recall of objects and their spatial locations. In contrast, the temporal lobe patients in Smith and Milner’s (1984) study showed impaired recall on both measures, but did not have difficulty making realistic estimations. Comparison with Developmental

Studies

In addition, the performance of ADHD children on the FL-sensitive measures was developmentally anomalous. Despite a mean age of about 10 years, ADHDs scores approximated those of 6- to S-year-old normal

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children (Becker et al., 1988; Chelune and Baer, 1986; Passler et al., 1985). Thus, our results are consistent with Chelune et al.‘s (1986) report that ADD children performed on the WCST at a level approximately 2 years behind their age-matched cohorts. Studies of normal children show a developmental gradient on performance of “FL” tasks. Like ADHDs, normal children younger than 8 years make significantly more errors and use simpler strategies than older children. The performance of 6- to 7year-old normal children resembles that of adult FL patients on the same tasks. Nature of the Deficit

Our results suggest that explanations of ADHD difficulties based on inhibitory (Chelune et al., 1986; Mattes, 1980) or attention control deficits (Gorenstein et al., 1989) are not sufficient to account for all the performance differences obtained. Although inhibitory deficits and heightened responsiveness to salient stimuli probably represent important components of the cognitive dysfunctions of ADHD children, neither provides a sufficient explanation. Several investigators have reported that ADHD children also demonstrate difficulties in such processes as problem solving, effective use of feedback, and generation and use of strategies (e.g., Dykman, Ackerman, & Oglesby, 1979; Hamlett, Pellegrini, & Conners, 1987; Tant & Douglas, 1982). Moreover, their inhibitory deficits are heightened when they are presented with complex or speeded tasks, thus increasing their tendency to respond to stimuli of greater salience (e.g., novel cues: Dykman et al., 1979; perceptual matching: ICD task in Study 1). Thus, hypotheses based solely on inhibitory or attentional deficits may address only partial aspects of a wider mechanism. Frontal cortex is a final end point for visual, auditory, and somesthetic sensory systems (Nauta, 1971). Information from the external environment is relayed there after analysis and processing by modality-specific and intermodal association regions. Neural connections also project to the frontal lobes from thalamic and limbic areas, providing information regarding relevant memories and internal states, such as affect and motivation. In addition to receiving external and internal information from cortical and subcortical regions, the frontal lobes have efferent connections to various sensory, motor, and subcortical areas. These efferent pathways are believed to play an important role in the monitoring and modulation of cortical sensory and motor areas and limbic functions (e.g., Nauta, 1971). Thus, the frontal lobes integrate relevant prior learning and motivational/affective states with current conditions and modulate responses appropriately. This integrative function is an important element of problem solving, responsiveness to reinforcement, response consistency, and other functions typically impaired in FL patients. Many terms have been used to label integrative failure in FL patients,

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including control and regulation, planning, organization, goal setting, selfregulation, self-monitoring, problem solving, and anticipation (e.g., Fuster, 1985; Luria, 1973; Nauta, 1971; Stuss & Benson, 1986). These terms all refer to higher level cognitive or “executive” skills (Pribram, 1973). This broader, more comprehensive hypothesis has the advantage of unifying the various performance deficits of FL patients, thus allowing anticipation of the types of deficits to be expected and conceptualization of treatment approaches. As an initial application of the FL analogy to ADHD, it may be theoretically and clinically useful to consider ADHD as an impairment of higher order cognitive processing. From this perspective, deficits such as attention, impulse control problems, and failure to inhibit responses to salient stimuli would be seen as resulting from difficulty integrating information in order to plan, set goals, monitor progress, anticipate outcomes, etc. Douglas (1983, 1985) has proposed a generalized defect in “self-regulatory control” to account for a number of the performance deficits of ADHD children. She suggests that this self-regulatory deficit is exhibited in attentional, inhibitory, arousal, and reinforcement abnormalities, thus explicitly emphasizing the interdependence of the impairments. Use of a frontal lobe analogy for ADHD would provide further support for this conceptualization of an underlying deficit in higher order cognitive processes. The term “self-regulation,” however, has been used most frequently to refer to an individual’s behavioral capacity to initiate or terminate activity appropriately (Lezak, 1983). It is most commonly assessed by measures of perseveration, cognitive flexibility, and response control. By specifying an “integrative” deficit, we are emphasizing the cognitive mechanism underlying inefficient “self-regulation” as well as other more complex higher order impairments. In addition to postulating a unified basis to the performance characteristics of FL patients, researchers have begun to relate specific anatomical loci in the frontal lobes to particular deficits. Petrides (1989) has suggested that specialized processing areas in the lateral frontal lobes play a part in organizing complex behavior, including such processes as monitoring a series of actions and recalling the order of occurrence of specific events. The orbital area of the frontal lobes, in contrast, seems more closely related to the limbothalamic memory system. It may be useful to relate these functional differences in FL “subsystems” to the deficits found in ADHD children. For example, ADHDs typically do not show difficulties on recognition memory tasks which are associated with ventromedial frontal cortex (e.g., Benezra & Douglas, 1988). In contrast, they are impaired on tasks associated with lateral frontal regions such as the WCST and SOP tasks. This dissociation, if

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confirmed by further research, would suggest that the functions served by the lateral frontal areas are most clearly implicated and would support the general conceptualization of ADHD as a problem in integrating, planning, and organizing. Frontal Lobe Development

Development of the frontal lobes is associated with increasing efficiency of information synthesis and activity modulation. Although this integrative capacity develops gradually, large gains occur between ages 8 and 12. The findings of Study 1 suggest that ADHD children with a mean age of 10 years have failed to develop integrative skills equal to those of agcmatched NCs or to those of normal lo-year-olds in developmental studies (Becker et al., 1988; Chelune and Baer, 1986; Passler et al., 1985). Longitudinal and cross-sectional studies of ADHD children could provide information on the rate and extent of development of “FL skills.” This information could also help determine whether the cognitive dysfunctions associated with ADHD represent a maturational lag (e.g., Chelune et al., 1986) or a permanent impairment. Neurological

Confirmation

Finally, if FL dysfunction is shown to be a viable neuropsychological model for ADHD, it will be necessary to discover whether the deficits shown by ADHD children on FL measures are a consequence of actual FL dysfunction. This will require the use of physiological measures such as positron emission tomography (e.g., Buchsbaum et al., 1982; Roland, 1984), regional cerebral blood flow (e.g., Weinberger et al., 1986), or brain electrical activity mapping (e.g., Duffy, Denckla, Bartels, & Sandini, 1980; Duffy, Denckla, Bartels, Sandini, & Kiessling, 1980). REFERENCES American Psychiatric Association 1Y87. Diagnosiic and statistical manual of mental disordeu. Washington, DC: American Psychiatric Association. Third edition. Revised. August, G. J. 1987. Production deficiencies in free recall: A comparison of hyperactive. learning-disabled. and normal children. Journal of Abnormal Child Psychology, E(3).

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