Computerized surgical navigation resection of pelvic region simulated bone tumors using skin fiducial marker registration: an in vitro cadaveric study.

INTRODUCTION: Computerized surgical navigation system guidance can improve bone tumor surgical resection accuracy. This study compared the 10-mm planned resection margin agreement between simulated pelvic-region bone tumors (SPBT) resected using either skin fiducial markers or Kirschner (K)-wires inserted directly into osseous landmarks with navigational system registration under direct observation. We hypothesized that skin fiducial markers would display similar resection margin accuracy. METHODS: Six cadaveric pelvises had one SPBT implanted into each supra-acetabular region. At the left hemi-pelvis, the skin fiducial marker group had guidance from markers placed over the pubic tubercle, the anterior superior iliac spine, the central and more posterior iliac crest, and the greater trochanter (5 markers). At the right hemi-pelvis, the K-wire group had guidance from 1.4-mm-diameter wires inserted into the pubic tubercle, and 3 inserted along the iliac crest (4 K-wires). The senior author, a fellowship-trained surgeon performed "en bloc" SPBT resections. The primary investigator, blinded to group assignment, measured actual resection margins. RESULTS: Twenty of 22 resection margins (91%) in the skin fiducial marker group were within the Bland-Altman plot 95% confidence interval for actual-planned margin mean difference (mean = -0.23 mm; 95% confidence intervals = 2.8 mm, - 3.3 mm). Twenty-one of 22 resection margins (95%) in the K-wire group were within the 95% confidence interval of actual-planned margin mean difference (mean = 0.26 mm; 95% confidence intervals = 1.7 mm, - 1.1 mm). CONCLUSION: Pelvic bone tumor resection with navigational guidance from skin fiducial markers placed over osseous landmarks provided similar accuracy to K-wires inserted into osseous landmarks. Further in vitro studies with different SPBT dimensions/locations and clinical studies will better delineate use efficacy.

A feasibility cadaver study for placing screws in various pelvic osseous fracture pathways using a robotic arm.

INTRODUCTION: The use of a robotic system for the placement of pedicle screws in spine surgeries is well documented in the literature. However, there is only a single report in the United States describing the use of a robotic system to place two screws in osseous fixation pathways (OFPs) commonly used in the treatment of pelvic and acetabular fractures in a simulated bone model. The purpose of this study was to demonstrate the use of a robotic system to place screws in multiple, clinically relevant OFPs in a cadaveric model and to quantitatively measure accuracy of screw placement relative to the preoperative plan. METHODS: A single cadaveric specimen was obtained for the purpose of this study. All surrounding soft tissues were left intact. Screws were placed in OFPs, namely iliosacral (IS), trans-sacral (TS), Lateral Compression-II (LC-II), antegrade anterior column (AC) and antegrade posterior column (PC) of the right hemipelvis using standard, fluoroscopically assisted percutaneous or mini-open technique. Following the placement of screws into the right hemipelvis using standard techniques, screws were planned and placed in the same OFPs of the contralateral hemipelvis using the commercially available ExcelsiusGPS® robotic system (Globus Medical Inc., Audubon, PA). After robotic-assisted screw placement, a post-procedure CT scan was obtained to evaluate actual screw placement against the pre-procedure plan. A custom-made image analysis program was devised to measure screw tip/tail offset and angular offset on axial and sagittal planes. RESULTS: For different OFPs, the mean tip offset, tail offset and angular offsets were 1.6 ± 0.9 mm (Range 0.0-3.6 mm), 1.4 ± 0.4 mm (Range 0.3-2.5 mm) and 1.1 ± 0.4° (Range 0.5-2.1), respectively. CONCLUSION: In this feasibility study, surgeons were able to place screws into the clinically relevant fracture pathways of the pelvis using ExcelsiusGPS® for robotic-assisted surgery. The measured accuracy was encouraging; however, further investigation is needed to demonstrate that robotic-assisted surgery can be used to successfully place the screws in the bony corridors of the pelvis to treat traumatic pelvic injuries.

The Use of a Robotic Arm for Fixation of Pelvic Fractures.

OBJECTIVES: The objective of this study was to evaluate unplanned cortical or neuroforaminal violation of iliosacral and transsacral screw placement using fluoroscopy versus screw placement using a robotic arm. DESIGN: This is a prospective cohort study. SETTING: Single surgeon, single North American level 1 trauma center. PATIENTS: Radiographic and clinical data for 21 consecutive adult trauma patients with pelvic ring fractures undergoing surgical treatment were prospectively collected. Treatment consisted of iliosacral and/or transsacral screws with or without anterior fixation. INTERVENTION: Ten patients were treated with the assistance of a robotic arm. Eleven patients were treated with standard fluoroscopic techniques. MAIN OUTCOME MEASUREMENTS: Thirty-two screws were placed and evaluated with postoperative computed tomography or O-arm spins to assess unplanned cortical or neuroforaminal violation. Violations were graded according to the Gertzbein and Robbins system for pedicle screw violation, categorizing screw violation in 2-mm increments. The postoperative images were blindly reviewed by 5 fellowship-trained orthopaedic traumatologists. The treating surgeon was excluded from review. RESULTS: The Mann-Whitney U test on the Gertzbein and Robbins system results demonstrated significantly (P = 0.02) fewer violations with robotic assistance. χ2 analysis of whether there was a cortical violation of any distance demonstrated significantly (P = 0.003) fewer cortical violations with robotic assistance. There were no neurovascular injuries in either group. CONCLUSION: Robotic assistance demonstrated significantly fewer unplanned cortical or neuroforaminal violations. Further research is needed with additional surgeons and sites to evaluate the accuracy of iliosacral and transsacral screw placement with robotic assistance. LEVEL OF EVIDENCE: Therapeutic, level II.

Free Hip Arthroplasty Templating Software - Does it Work?

Background: Preoperative planning is important for successful total hip arthroplasty (THA) and has been historically performed using acetate templates. Digital software templating has been adopted for evaluating implant size, position, and alignment. Commercial software can be expensive, but free programs exist. Detroit Bone Setter (detroitbonesetter.com, Detroit, MI) is a freely available templating program, but hasn't been validated. Our study reports this program's accuracy for templating THA. Methods: Sixty-five patients undergoing THA between 2017 and 2022 at 2 hospitals were included. All cases were templated by the senior author or orthopaedic trauma fellow prospectively or retrospectively in a blinded fashion. Direct anterior or posterior approaches were used based on attending surgeon's preference. A student's t-test was used to compare means of templated vs actual implant sizes of femoral and acetabular components. Results: There was no significant difference between implanted (mean [M] = 6.4, standard deviation [SD] = 2.0) and templated femoral component sizes (M = 5.7, SD = 2.1). There was a significant difference between implanted (M = 57.0, SD = 3.9) and templated acetabular component sizes (M = 53.4, SD = 3.0). Bland-Altman testing demonstrated femoral components with positive measurement bias of 0.62, indicating slight overestimation of implant size. Acetabular component size was overestimated with positive measurement bias of 3.6 mm. Conclusions: Detroit Bone Setter is advantageous as it is freely available and supports most major company implants. It accurately templated femoral component size but consistently overestimated acetabular component size by 3.6 mm. Further studies are needed prior to recommending its routine use for templating THA when other validated methods exist. It could be used with caution when no other methods are available.

Robotic-assisted percutaneous pelvis fixation: A case report.

Key Clinical Message: It may be possible to extend the use of the robotic arm to pelvic and acetabular surgery leading to safe, repeatable screw placement, and less radiation exposure for patients, surgeons and OR staff. Abstract: In this case, a novel, robotic-assisted technique was used to place a sacroiliac screw in a patient with unstable injuries of the pelvic ring. Intraoperative and postoperative fluoroscopic, radiographic, and CT imaging demonstrated a safely positioned 6.5 mm cannulated screw without unplanned cortical violation or impingement on neurovascular structures. To our knowledge, this is the first such reported case using a robot widely available in the Americas or Europe.

Placement of LC-II and trans-sacral screws using a robotic arm in a simulated bone model in the supine position - a feasibility study.

PURPOSE: The use of a robotic arm has been well-described in the literature for the placement of pedicle screws in spine surgery as well as implants for sacroiliac joint fusion. There are no reports describing the use of a robotic arm to place screws in osseous fixation pathways (OFPs) employed in the treatment of pelvic ring and acetabular fractures outside of a single center in China. Using a Sawbones model, the authors describe a technique for using a robotic arm widely available in Europe and the Americas for placement of 6.5 mm cannulated screws into two OFPs commonly used in the treatment of pelvic and acetabular fractures. METHODS: Using the Mazor X Stealth Edition (MSXE) robot from Medtronic, the authors were able to place a pin into the pelvis onto which the robot was docked. The authors were then able to designate the area of interest using navigated instruments, and in combination with the MSXE "scan and plan" marker, obtain cross-sectional imaging using the O-Arm and successfully register the MSXE robot. We then used the provided software to plan trajectories for the lateral compression type 2 (LC-II) screw pathway as well as a pathway for a trans-ilio-trans-sacral screw. We describe in detail the steps for setup, planning and placement of 6.5 mm cannulated screws using the MSXE robotic arm into these two OFPs. RESULTS: Visual inspection and plain x-rays demonstrated successful placement of the screws into the two planned OFPs. No breach of cortical bone was seen on either visual inspection of the model or demonstrated on post-procedure x-rays. CONCLUSION: It is possible to use the Mazor X Stealth Edition robot to place screws into the LC-II and trans-ilio-transsacral screw pathways in a Sawbones model. This is only a feasibility study, and should in no way be taken to suggest that clinical application of this technique should be attempted.

Immediate outcomes of early versus late definitive fixation of acetabular fractures: A narrative literature review.

The ideal timing of acetabular fractures fixation remains contentious. Early immediate fixation was thought to increase the surgery duration and blood loss while facilitating earlier mobilization and shorter hospital stay; and vice versa for the late fixation after 7 days. The purpose of this review was to compare the impact of early (defined as within 48 hours) versus later definitive fixation of acetabular fractures on postoperative outcomes. It was found that early surgical treatment has certain advantages with regards to blood loss, operative time, and LOS especially in patients with lower ISS. However, further studies are necessary to provide more evidence in terms of long-term outcomes.

The Neurostimulation Appropriateness Consensus Committee (NACC): Recommendations on Best Practices for Cervical Neurostimulation.

INTRODUCTION: The International Neuromodulation Society convened a multispecialty group of physicians based on expertise with international representation to establish evidence-based guidance on the use of neurostimulation in the cervical region to improve outcomes. This Neurostimulation Appropriateness Consensus Committee (NACC) project intends to provide evidence-based guidance for an often-overlooked area of neurostimulation practice. MATERIALS AND METHODS: Authors were chosen based upon their clinical expertise, familiarity with the peer-reviewed literature, research productivity, and contributions to the neuromodulation literature. Section leaders supervised literature searches of MEDLINE, BioMed Central, Current Contents Connect, Embase, International Pharmaceutical Abstracts, Web of Science, Google Scholar, and PubMed from 2017 (when NACC last published guidelines) to the present. Identified studies were graded using the US Preventive Services Task Force criteria for evidence and certainty of net benefit. Recommendations are based on the strength of evidence or consensus when evidence was scant. RESULTS: The NACC examined the published literature and established evidence- and consensus-based recommendations to guide best practices. Additional guidance will occur as new evidence is developed in future iterations of this process. CONCLUSIONS: The NACC recommends best practices regarding the use of cervical neuromodulation to improve safety and efficacy. The evidence- and consensus-based recommendations should be utilized as a guide to assist decision making when clinically appropriate.

Tibia fractures and NSAIDs. Does it make a difference? A multicenter retrospective study.

PURPOSE: The purpose of this study was to compare healing time for diaphyseal tibia fractures (OTA/AO 42 A, B, C) treated with intramedullary nailing (IMN) in one geographic cohort using nonsteroidal anti-inflammatory drugs (NSAIDs) for post-operative pain control to that of another geographic cohort using opioid medications. The groups represent differing cultural approaches to post-operative pain control. We hypothesized there would be no difference in healing time. METHODS: Tibia fractures presenting at two level I trauma centers located in different countries between January 1, 2010 and December 31, 2017 were retrospectively screened for enrollment. Fractures classified as OTA/AO 42 A, B, or C that were treated with IMN and had radiographic follow up to union were included. At hospital discharge, one cohort (n = 190) was prescribed NSAIDs and the other (n = 182) was prescribed opioids for pain control. Each analgesic method represented the standard of care for that location. Fracture union was defined as cortical bridging in at least 3 out of 4 cortices on AP and lateral radiographs. The primary outcome was healing time on radiographic evaluation. RESULTS: There was no statistically significant difference in healing time between the opioid and NSAID groups: 185 vs 180.5 days respectively (p = 0.64). Both groups had similar mean age. Student t-tests were run to compare rates of tobacco use, diabetes mellitus (DM), open fractures, and polytrauma between the two groups. The opioid cohort had statistically significant higher rates of tobacco use, DM, and polytrauma. The NSAID cohort, however, had a larger number of open fractures. CONCLUSION: The difference in healing time between the NSAID and opioid groups was not statistically significant. The deleterious effect of NSAID use on fracture healing has been debated for decades. Numerous animal studies have supported this theory; however, high quality clinical studies in humans have not provided convincing evidence to substantiate this negative effect. Our study suggests that NSAIDs may be used safely and effectively in the acute phase of fracture healing without significantly increasing the risk of delayed union or nonunion. Prospective randomized studies are necessary to rule out the negative effect of NSAIDS on bone healing.

Skin fiducial markers enable accurate computerized navigation resection of simulated soft tissue tumors: A static cadaveric model pilot study.

BACKGROUND: This static cadaveric model pilot study evaluated the agreement between planned and resected margins of simulated soft tissue tumors (SSTT) using skin fiducial markers for computerized navigation registration. METHODS: Markers were applied before magnetic resonance imaging scans of lower extremities implanted with SSTT. A navigation pointer was used for registration and to guide SSTT resection with approximately 10 mm planned margins. Digital calipers were used to measure resection margins. Kolmogorov-Smirnov tests were used to confirm measurement normality. A one-sample t test was used to determine measurement group differences (P ≤ 0.05). Bland-Altman analysis and histogram plots compared planned and resected margins. RESULTS: Ninety-eight resection margins were measured. The planned margin mean was 10.0 mm (95% confidence interval [CI] = 9.8-10.2 mm) and the resected margin mean was 11.5 mm (95% CI = 11.0-12.1 mm). One-sample t test results identified a 0.75 mm, 95% CI = 0.5-0.99 mm difference (P < 0.001). Good measurement agreement was observed with 94.9% (93/98) of resections occurring within two standard deviations of the mean measurement difference. CONCLUSIONS: Skin fiducial marker use for computerized navigation system registration displayed promising results. With further research, these markers may become an effective, noninvasive method for aiding in soft tissue tumor resection.

Midterm Radiographic and Functional Outcomes of the Anterior Subcutaneous Internal Pelvic Fixator (INFIX) for Pelvic Ring Injuries.

OBJECTIVE: To describe our experience using the anterior internal pelvic fixator (INFIX) for treating pelvic ring injuries. DESIGN: Case Series. SETTING: Level 1 Trauma Center. PATIENTS: Eighty-three patients with pelvic ring injuries were treated with INFIX. Follow-up average was 35 months (range 12-80.33). INTERVENTION: Surgical treatment of pelvic ring injuries included reduction, appropriate posterior fixation, and INFIX placement. OUTCOME MEASUREMENTS: Reduction using the pelvic deformity index and pubic symphysis widening, Majeed functional scores, complications; infection, implant failure, heterotopic ossification (HO), nerve injury, and pain. RESULTS: All patients healed in an appropriate time frame (full weight bearing 12 weeks postoperation). The average pelvic deformity index reduction (injury = 0.0420 ± 0.0412, latest FU = 0.0254 ± 0.0243) was 39.58%. The average reduction of pubic symphysis injuries was 56.92%. The average Majeed score of patients at latest follow-up was 78.77 (range 47-100). Complications were 3 infections, 1 case of implant failure, 2 cases implantation too deep, 7 cases of lateral femoral cutaneous nerve irritation, and 3 cases of pain associated with the device. HO was seen in >50% of the patients, correlated with increased age (P < 0.007), injury severity score (P < 0.05) but only 1 case was symptomatic. CONCLUSIONS: The pelvic injuries had good functional and radiological outcomes with INFIX and the appropriate posterior fixation. The downside is removal requiring a second anesthetic, there is a learning curve, HO often occurs, the lateral femoral cutaneous nerve may get irritated which often resolves once the implants are removed. Surgery-specific implants need to be developed. LEVEL OF EVIDENCE: Therapeutic Level IV. See Instructions for Authors for a complete description of levels of evidence.

Accuracy of Low Dose Computed Tomography Scanogram for Measurement of Femoral Version after Locked Intramedullary Nailing.

PURPOSE: This prospective study was performed to compare the accuracy of femoral version measurements following repair of femoral shaft fractures using computed tomography (CT) scanograms with 10 % of the standard dose of ionizing radiation versus standard-dose scanograms. METHODS: CT scanogram protocols that used 90 and 10 % of the usual dose of ionizing radiation were developed. Ten patients with comminuted femoral shaft fractures repaired with either an intramedullary (IM) nail or plate were imaged with both high- and low-dose CT scanograms. Postoperative version of both femurs was measured and compared between the two dose scans using the Bonesetter application. This was a prospective blinded controlled study at a level 1 trauma centre. Statistical analysis was performed, including standard deviation (SD) and paired t test. Significance was set at p < 0.05. RESULTS: Comparison of femoral version measurements between the 90 and 10 % dose scanograms on the native and repaired sides were insignificant (p = 0.870 and p = 0.737, respectively). The difference between native and repaired femurs had an average error of 2.0 ± 1.1° for both the high- and low-dose scans and was insignificant (p = 0.742). CONCLUSIONS: Reducing the dose of ionizing radiation in a CT scanogram by 90 % has no significant effect on the accuracy of femoral version measurement. This simple change can significantly reduce patient radiation exposure while accurately measuring femoral version and length.

Prognostic subgroups for remission, response, and treatment continuation in the Clinical Antipsychotic Trials of Intervention Effectiveness (CATIE) trial.

OBJECTIVE: Identify moderators of treatment outcome from antipsychotic pharmacotherapy in the Clinical Antipsychotic Trials of Intervention Effectiveness (CATIE) trial. Specifically, we used logistic regression and receiver operating characteristic (ROC) analysis to explore the association between baseline characteristics and treatment outcomes in the CATIE trial. METHOD: This is a secondary analysis of the CATIE trial in which 1,460 adults with a DSM-IV diagnosis of schizophrenia were randomly assigned to olanzapine, perphenazine, quetiapine, risperidone, or ziprasidone treatment for up to 18 months or until discontinuation between January 2001 and December 2004. Logistic regression was used to examine baseline characteristics associated with remission, response, and treatment continuation at 3 and 6 months of treatment. ROC analyses identified subgroups associated with similar likelihood of treatment outcome. Remission was defined by scores of selected items on psychoticism, disorganization, and negative symptoms. Response was defined as a 50% or greater improvement on the Positive and Negative Syndrome Scale. RESULTS: The most consistent predictors of poor outcome on all variables were low scores on neurocognitive tests (in particular verbal memory) (OR = 1.13-1.49, P< .05); previous reported side effects (OR = 0.49-0.69, P < .05); negative attitude to medication (OR = 1.03-1.10, P < .05); comorbid depression (OR = 0.47-0.51, P < .05); psychosocial factors such as unemployment (OR = 0.74-0.75, P <.05), homelessness (OR = 0.54, P <.05), and living alone (OR = 1.58-1.94, P < .01); and random assignment to a medication other than olanzapine (OR = 1.54-2.04, P < .01). ROC analysis demonstrated prognostic subgroups with large differences in response likelihood. CONCLUSION: Baseline characteristics in schizophrenia are informative regarding clinically important treatment outcomes with respect to antipsychotic pharmacotherapy. Further research should examine whether interventions that target improvement of patients' deficits in neuropsychological function and attitude toward medication as well as decreasing patients' social isolation can improve treatment outcomes with antipsychotic treatment in schizophrenia. TRIAL REGISTRATION: ClinicalTrials.gov identifier: NCT00014001.

Going up in smoke? A review of nAChRs-based treatment strategies for improving cognition in schizophrenia.

Cognitive impairment is known to be a core deficit in schizophrenia. Existing treatments for schizophrenia have limited efficacy against cognitive impairment. The ubiquitous use of nicotine in this population is thought to reflect an attempt by patients to selfmedicate certain symptoms associated with the illness. Concurrently there is evidence that nicotinic receptors that have lower affinity for nicotine are more important in cognition. Therefore, a number of medications that target nicotinic acetylcholine receptors (nAChRs) have been tested or are in development. In this article we summarize the clinical evidence of nAChRs dysfunction in schizophrenia and review clinical studies testing either nicotine or nicotinic medications for the treatment of cognitive impairment in schizophrenia. Some evidence suggests beneficial effects of nAChRs based treatments for the attentional deficits associated with schizophrenia. Standardized cognitive test batteries have failed to capture consistent improvements from drugs acting at nAChRs. However, more proximal measures of brain function, such as ERPs relevant to information processing impairments in schizophrenia, have shown some benefit. Further work is necessary to conclude that nAChRs based treatments are of clinical utility in the treatment of cognitive deficits of schizophrenia.

In vivo evidence for ß2 nicotinic acetylcholine receptor subunit upregulation in smokers as compared with nonsmokers with schizophrenia.

BACKGROUND: Schizophrenia is associated with very high rates of tobacco smoking. The latter may be related to an attempt to self-medicate symptoms and/or to alterations in function of high-affinity ß2-subunit-containing nicotinic acetylcholine receptors (ß2*-nAChRs). METHODS: Smoking and nonsmoking subjects with schizophrenia (n=31) and age-, smoking-, and sex-matched comparison subjects (n=31) participated in one [123I]5-IA-85380 single photon emission computed tomography scan to quantify ß2*-nAChR availability. Psychiatric, cognitive, nicotine craving, and mood assessments were obtained during active smoking, as well as smoking abstinence. RESULTS: There were no differences in smoking characteristics between smokers with and without schizophrenia. Subjects with schizophrenia had lower ß2*-nAChR availability relative to comparison group, and nonsmokers had lower ß2*-nAChR availability relative to smokers. However, there was no smoking by diagnosis interaction. Relative to nonsmokers with schizophrenia, smokers with schizophrenia had higher ß2*-nAChR availability in limited brain regions. In smokers with schizophrenia, higher ß2*-nAChR availability was associated with lower negative symptoms of schizophrenia and better performance on tests of executive control. Chronic exposure to antipsychotic drugs was not associated with changes in ß2*-nAChR availability in schizophrenia. CONCLUSIONS: Although subjects with schizophrenia have lower ß2*-nAChR availability relative to comparison group, smokers with schizophrenia appear to upregulate in the cortical regions. Lower receptor availability in smokers with schizophrenia in the cortical regions is associated with a greater number of negative symptoms and worse performance on tests of executive function, suggesting smoking subjects with schizophrenia who upregulate to a lesser degree may be at risk for poorer outcomes.

DSM-5 and the 'Psychosis Risk Syndrome': The DSM-5 proposal is better than DSM-IV.

The American Psychiatric Association is considering the inclusion of the psychosis risk syndrome as a new diagnosis for DSM-5. The main evidence supporting inclusion is: (1) the patients meet criteria for having a current illness, (2) the patients are at high risk for becoming more severely ill, (3) no DSM-IV diagnosis accurately captures their current symptoms or future risk, (4) the diagnosis is reliable and valid, at least in the research setting, and (5) codification in DSM-5 will promote treatment and prevention research of sufficient quantity and quality to permit the development of treatment guidelines. Field trials are needed to determine whether the proposed diagnostic criteria can be used with reliability in actual clinical practice.

Development of the 40Hz steady state auditory evoked magnetic field from ages 5 to 52.

OBJECTIVE: Adults exhibit strong auditory 40 Hz magnetic steady state responses (SSR). Although EEG measured SSR has been studied in children, the developmental course of the magnetic SSR is unknown. METHODS: Sixty-nine healthy subjects ranging in age from 5 to 52 years participated in a magnetoencephalographic (MEG) study. Stimuli were monaural 500 ms duration click trains with a 25 ms inter-click interval. Contralateral magnetic responses for both hemispheres were recorded with a 37-channel MEG system. Responses were averaged and examined using wavelet-based time-frequency analysis. Source analyses were also conducted on a subset of the data. RESULTS: Gamma power from 200 to 500 ms post-stimulus onset was computed and was significantly related to subject age in both hemispheres. Hemispheric asymmetry was observed for the anterior-posterior SSR source locations, suggestive of asymmetry similar to that previously described for the SSR and other auditory evoked magnetic field components. CONCLUSIONS: The 40 Hz power findings are generally consistent with previous EEG studies of steady state responses in children showing age-related changes in the 40 Hz SSR. SIGNIFICANCE: Age-related changes in the strength of the magnetic 40 Hz SSR may continue to develop well beyond early childhood, which should be taken into consideration in planning future studies using adolescents and young adults.

Reduced laterality of the source locations for generators of the auditory steady-state field in schizophrenia.

BACKGROUND: Reduced hemispheric asymmetry of evoked field generators in schizophrenia in secondary auditory cortex has been replicated with mixed success. This disparity is possibly due to the complex nature of the 100-msec generators typically investigated. In this study, we evaluated a source located in primary auditory cortex, responsible for the steady-state response, to determine whether similar asymmetries were present. METHODS: Contralateral evoked fields were recorded with a 37-channel neuromagnetometer in response to 40-Hz pulse trains. Dipole models were used to localize the sources in both hemispheres of schizophrenic subjects (n = 17) and normal control subjects (n = 18). RESULTS: Control subjects were asymmetrically lateralized, with sources in the right hemisphere approximately 6 mm further anterior than those on the left. In contrast, schizophrenic subjects showed no significant difference between hemispheres. CONCLUSIONS: The findings support theories linking schizophrenia to disturbed asymmetry of temporal lobe function. The steady-state response, having a more discrete Heschl's gyrus generator location, may be better suited for evaluating auditory asymmetry.