Subfascial implantation of intrathecal baclofen pumps in children: technical note.

OBJECTIVE: Indwelling intrathecal drug delivery systems are becoming increasingly important as a method of neuromodulation within the nervous system. In particular, intrathecal baclofen therapy has shown efficacy and safety in the management of spasticity and dystonia in children. The most common complications leading to explantation of the pumps are skin breakdown and infection at the pump implantation site. The pediatric population poses particular challenges with regard to these complications because appropriate candidates for intrathecal baclofen therapy are often undernourished and thus have a dearth of soft tissue mass to cover a subcutaneously implanted baclofen pump. We report a technique of subfascial implantation that provides greater soft tissue coverage of the pump, thereby reducing the potential for skin breakdown and improving the cosmetic appearance of the implantation site. METHODS: Eighteen consecutively treated children (average age, 8 yr, 7 mo) with spasticity and/or dystonia underwent subfascial implantation of a baclofen pump. These children's mean weight of 42.9 lb is less than the expected weight for a group of children in this age group, ranging from 4 years, 8 months, to 15 years, 7 months. In all patients, the pump was inserted into a pocket surgically constructed between the rectus abdominus and the external oblique muscles and the respective anterior fascial layers. RESULTS: At an average follow-up of 13.7 months, no infection or skin breakdown had occurred at the pump surgical site in any of the 18 patients. CONCLUSION: At this early follow-up, the subfascial implantation technique was associated with a reduced rate of local wound and pump infections and provided optimal cosmetic results as compared with that observed in retrospective cases.

Complications of deep brain stimulation surgery.

Although technological advances have reduced device-related complications, DBS surgery still carries a significant risk of transient and permanent complications. We report our experience in 86 patients and 149 DBS implants. Patients with Parkinson's disease, essential tremor and dystonia were treated. There were 8 perioperative, 8 postoperative, 9 hardware-related complications and 4 stimulation-induced side effects. Only 5 patients (6%) sustained some persistent neurological sequelae, however, 26 of the 86 patients undergoing 149 DBS implants in this series experienced some untoward event with the procedure. Although there were no fatalities or permanent severe disabilities encountered, it is important to extend the informed consent to include all potential complications.

Auditory event-related potentials while ignoring tone stimuli: attentional differences reflected in stimulus intensity and latency responses in low and highly hypnotizable persons.

Effect of hypnotic susceptibility level on auditory event-related potentials (AERPs) was studied as subjects were instructed to ignore tones while reading a novel or counting one's pulse. Assessed previously on two hypnotic susceptibility scales [Harvard Group Scale of Hypnotic Susceptibility; Stanford Hypnotic Susceptibility Scale, Form C (SHSSC)], subjects were 12 low (lows; SHSSC 0-2) and 12 highly (highs; SHSSC 9-12) hypnotizable, right-handed college students. AERPs were recorded at C3, C4, and Cz to 50 ms 1.961 tone pips 50, 60, 70 and 80 dB intensities, pseudorandomly presented at 1.5 intervals. As predicted, highs had significantly smaller N1 and P2 amplitudes than did lows when ignoring tones. As stimuli intensities increased, N1 latencies decreased for lows while N1 latencies increased for highs. N1 latency slopes across the 50 to 80 dB intensities were significantly more negative for lows than highs; slopes correlated significantly with both hypnotizability and absorption (Tellegen Absorption Scale). Thus, the highs appeared to divert greater attentional processing to the tasks at hand, particularly as the tones increased in intensity, and were slower to respond to not-to-be-attended stimuli. These results are interpreted as further evidence for hypnotic susceptibility being associated with efficient attentional processing such that highs can more effectively partition attention towards relevant stimuli and away from irrelevant stimuli than can low hypnotizables.

Apparent response incompatibility effects on P3 latency depend on the task.

Ten young women were tested with an ERP paradigm that used the words 'left,' 'right,' 'LEFT,' 'RIGHT' as stimuli. The stimulus sequence was presented as several separate runs with varying response instructions. Subjects were instructed to respond according to the meaning of the stimulus in the (WORD task), to the case in which the stimulus was written (CASE task), or to both the case and meaning of the stimulus (CASE/WORD) task. In each task, half the trials called for a response that was incompatible with the stimulus. For the WORD task, compatible and incompatible trials were presented as separate blocks of trials. For all 3 tasks an additional stimulus sequence was presented in which the words were degraded with superimposed visual random noise. Reaction time (RT) in the CASE/WORD task was more than 100 msec later than in the other tasks. In the WORD and CASE/WORD tasks, RT was delayed more than 100 msec when the response was incompatible with the stimulus. Degrading the stimulus additionally delayed RT by about 100 msec. In the WORD and CASE tasks, error RTs were earlier than correct RTs. P3 latency was measured with a single-trial latency adjustment algorithm. P3 latency was delayed in the CASE/WORD task compared to the other 2 tasks. P3 was delayed by degrading the stimuli. Contrary to some previous reports, P3 was delayed by about 70 msec when incompatible responses were required, but only in the WORD task. Taken together with error and RT data, these P3 latency data are consistent with the notion that the task causes subjects to adopt different strategies and hence different types of processing (i.e., serial vs. parallel). Depending on the type of processing, P3 may appear to be affected by response incompatibility.

ERPs to response production and inhibition.

Three experiments investigating the effects of response production and inhibition on the N2 and P3 components of the ERP are reported. In the first experiment, 12 young female volunteers were presented with the words "push' and "wait' (semantic stimuli). On a separate series of trials, they were presented with arbitrary symbols assigned the same meanings (symbolic stimuli). For each stimulus series half of the stimuli were degraded. To obtain an estimate of reliability of the data, each task was repeated. Data were collected from Fz, Cz and Pz electrode sites. The P3 amplitude had a parietal maximum when the stimuli instructed subjects to respond (Go). The P3 was equal at central and parietal sites when the stimuli instructed the subjects to withhold a response (No-Go). This topographic pattern was obtained for all stimulus manipulations, simple and degraded stimuli, words and symbols, and for the first and second runs. The N2 was a frontal maximum component that was larger to the No-Go than to the Go stimuli. This result was also robust to the manipulations. A second experiment investigated the dependency of these findings on an overt motor response. In this experiment, the symbolic and semantic stimulus series were each presented twice. The subjects counted the Go stimuli and did not count the No-Go stimuli for one presentation and pressed the reaction time button as in experiment 1 for the other presentation. While counting (compared to button pressing) delayed the N2 and P3 peaks, counting and pressing produced similar results, including the Go/No-Go P3 distribution effects. A third experiment investigated the sensitivity of these findings to the orientation of the symbols instructing the subjects to respond or withhold the response. Again the pattern of results was robust to this manipulation.

Clinical application of the P3 component of event-related potentials. II. Dementia, depression and schizophrenia.

Patients with dementia, schizophrenia and depression were tested with analogous auditory and visual event-related potential (ERP) paradigms designed to elicit a large P3. The patient groups were compared to age normative predictions derived from a large control sample for a number of ERP and behavioral variables. The results were similar for the auditory and visual paradigms. P3 latency was prolonged two or more S.D.s beyond that predicted by age for less than one-half of the demented patients. This latency prolongation was significant for the group as a whole but would result in too many false negatives if used diagnostically for individuals. Furthermore, increased P3 latency was not specific, as the schizophrenic patients also had later P3s. The amplitude of P3 was reduced in the demented patients, but it was also smaller in other patient groups. The only variable which distinguished the demented patients from both controls and from the other patients was the single trial P3 latency/RT correlation. The demented patients, as a group, had significantly lower P3 latency/RT correlations, but this effect also was not sensitive enough to be diagnostic for individuals. The data from these two paradigms suggest that the P3 amplitude and latency abnormalities observed reflect a common, rather than a diagnostically specific deficit. This study is in contrast to some others which report much more sensitivity and specificity in the use of P3 latency in the diagnosis of dementia. Differences in task demands, patient samples and ERP analysis techniques might explain some of the discrepancy.

Clinical application of the P3 component of event-related potentials. I. Normal aging.

Normal adult volunteer subjects ranging in age from 18 to 90 years participated in a study in which analogous auditory and visual paradigms, with infrequently occurring target and non-target events, were used to elicit event-related potentials (ERPs) with a prominent P3 component. Of the 135 subjects participating, 66 completed both auditory and visual paradigms. The amplitude and latency of P3 were analyzed using average ERPs, single trials (adaptive filter) and principal components analysis (PCA). Age regressions were calculated using measures derived from average ERPs and single trials. Single trial measures were better than average ERP measures in demonstrating age-related changes in P3 latency. There was a significant increase in P3 latency with age of 1-1.5 msec/year. The range of normal P3 latency for a given age (1 S.E. of the regression = 40 msec for the visual target stimuli) was much larger than obtained by other investigators. The visual paradigm produced higher P3 latency/age correlations than the auditory paradigm (visual target r = 0.52, non-target r = 0.42; auditory target r = 0.32, non-target r = 0.33). Within individuals, the amplitude and latency of P3 generated by auditory and visual stimuli were highly correlated, though the visual paradigm produced larger and later P3s than the auditory paradigm. There is an apparent change in the scalp topography of P3 with age. In young adults, P3s to target stimuli have a markedly parietal distribution. The distribution of P3 becomes more uniformly distributed from Pz to Fz with age. This may be due to changes in overlapping components such as the slow wave (SW) rather than to changes in the amplitude of P3 per se.

Manipulation of P3 latency: speed vs. accuracy instructions.

Twelve young female subjects were presented with a series of horizontal line-pairs of same or different length in a two-alternative, forced-choice RT task, with 60 of each type pair in each block of trials. In one block (Easy) lines differed by 30%, in another block (Difficult) lines differed by 7%. Subjects were first given 60 practice trials with the Easy discrimination and with the instruction that speed and accuracy should be emphasized equally. For the next block of trials, accuracy was emphasized with a monetary bonus for accurate performance. Finally, in the last block of trials, speed was emphasized with a monetary bonus for speedy performance. Additionally, a penalty was incurred for RTs that exceeded a criterion level based on each individual subject's performance. The order of Easy and Difficult discrimination blocks was maintained within a subject but balanced across subjects. From the latency-adjusted P3s recorded from Pz, we obtained P3 latencies, amplitudes and single-trial P3 latency/RT correlations. RT to correct and incorrect trials and error data were also collected. P3 was considerably larger during the Speed than Accuracy conditions. The single-trial P3 latency/RT correlation was higher in Speed than in Accuracy runs. RT was 235 msec faster and P3 was 40 msec earlier during the Speed than during the Accuracy runs. On the other hand, discrimination difficulty delayed P3 and RT about equally, 28 and 43 msec respectively. This pattern suggests that speed instructions and discrimination difficulty affect stimulus processing time and response production time differently.

Expectancy for events in old age: stimulus sequence effects on P300 and reaction time.

Event-related brain potentials were collected from 10 young (M = 22 years) and 10 elderly (M = 77 years) women. Stimuli were random sequences of 1000- and 1500-Hz tone pips in a two alternative, forced choice, reaction time task. Trials were sorted and averaged according to the sequence of the preceding four tones: continuations of repetitions (AAAAA) and alternations (ABABA) and discontinuations of repetitions (BBBBA) and alternations (BABAA). For both groups the P300 component of the event-related brain elicited larger P300s than did discontinuations of alternations, an effect especially large for the elderly women. Mean reaction time did not differ between the two groups, although P300 latencies were significantly longer for the elderly group. Results are discussed in terms of age-related differences in response strategies and sensitivity of P300 latency to response strategy.

Effects of perceptual and cognitive difficulty on P3 and RT in young and old adults.

Ten healthy old and 10 healthy young subjects each received a series of trials in a memory retrieval task similar to that devised by Sternberg (1967). On each trial the subject saw a memory set of 2 or 4 digits (set size) followed by a probe. The task was to indicate whether the probe was a positive or negative instance (response type) of the memory set for that trial. On half the trials, the probe digits were degraded by a mask of random dots (stimulus quality). For both young and old subjects, RT was later to probes following the larger set size, later to degraded probes, and later to negative probes. For the young subjects only, P3 latency was delayed by the same variables affecting RT although to a lesser degree. P3 latency in the elderly responded quite differently: it was unaffected by set size or response type. However, P3 was somewhat delayed by the degraded probes suggesting that the failure to reflect set size or ceiling effect in the elderly. The correlation between single-trial P3 latency and RT in the elderly is lower than in the young. The data are discussed in terms of age-related differences in the meaning of P3 latency.

Auditory event-related potentials in schizophrenia and depression.

Event-related potentials in two auditory target detection paradigms and two auditory paradigms without overt tasks were studied in 22 schizophrenic, 21 depressed, and 28 matched control subjects meeting Research Diagnostic Criteria. In the target detection paradigms, schizophrenics showed a pattern of reduced N120 amplitude and shorter P200 latency to frequently occurring tones, and reduced P300 and Slow Wave amplitude to infrequent target and nontarget tones. This pattern is consistent with impaired selective attention for stimuli. For depressed patients these variables were generally intermediate between those of schizophrenics and controls. In the other paradigms N120 latency was greater for schizophrenics, and P200 amplitude was less for depressed patients.

P3 reduction in auditory evoked potentials of schizophrenics.

Fifteen schizophrenics and 15 age-matched controls performed a reaction time (RT) task. A Bernoulli sequence of 85 dB SPL, 50 msec, 800 c/sec (P = 0.85) and 1200 c/sec (P = 0.15) tones was presented with an interstimulus interval of 1 sec. Subjects were instructed to press a button quickly upon hearing the 1200 c/sec tone. If a subject failed to respond within 650 msec, a 50 msec white noise burst occurred. In averages synchronized with target tones and computed without respect to RT, P3 was maximal at PZ with a mean latency of 330 msec for both schizophrenics and controls. P3 amplitude at PZ, however, averaged 6 muV in schizophrenics and 14 muV in controls (P < 0.001). Both mean RT and mean within-subject variance were greater in schizophrenices than controls. Other kinds of averages were computed to investigate the possibility that the amplitude differences were associated with different RTs or with differences in P3 latency variability in underlying trails. Averages of trials associated with short RTs (100--286 msec) had larger P3s than averages associated with long RTs (287--600 msec) (P < 0.01). Within each RT range, however, schizophrenic P3s were smaller than control P3s. Neither response-synchronized averaging nor adaptive filtering eliminated P3 amplitude differences between groups, indicating that P3 latency variability cannot account for these differences. We hypothesize that the smaller P3s in schizophrenics represent a deficit in reactivity to unexpected stimuli that is compatible with normal RT performance.