Mismatch field to tone pairs: neuromagnetic evidence for temporal integration at the sensory level

The mismatch field (MMF) to minor pitch changes in two experimental conditions was studied. Standard tones of 1000 Hz and deviant tones of 1050 Hz both of 50 ms duration were delivered in single tone condition. Paired tones of the same duration were used in the paired tone condition. The standard tone pair consisted of two 1000 Hz tones, whereas the deviant tone pair was composed of a 1000 Hz tone in the first position and a 1050 Hz tone in the second position with a silent interval of 15 ms between the two. Standards of 90% and deviants of 10% probability were presented in random order and with a randomized interstimulus interval between 600 and 900 ms. The source analysis showed a more lateral location for the MMF obtained in the paired tone condition (MMF.P) compared to the MMF elicited by the single deviants (MMF.S). The source location of both the MMF.P and MMF.S turned out to be significantly anterior relative to the sources of the M100. The increased stimulus repetition in the paired tone condition (two times more stimuli than in the single tone condition) lead to a strong suppression of the field amplitude and of the dipole moment of the M100, while this effect could not be seen for the MMF. The data demonstrate a fundamental difference between the processes reflected by the M100 and the MMF: while the M100 represents the processing of every individual tone, the MMF reflects the change detection of the paired stimuli as unitary events, forming a perceptual group. The different sources of the MMF.P and MMF.S also support an integrated processing of the paired stimuli.

Tonotopic organization of the sources of human auditory steady-state responses

Steady-state responses (SSRs) or steady-state fields (SSFs) show maximum amplitude when tone pulses are presented at repetition rates near 40 Hz. This result has led to the hypothesis that the SSR/SSF consists of superimposed transient 'middle latency' responses which display wave periods near 40 Hz and summate with one another when phase locked by 40 Hz steady-state stimulation. We evaluated this hypothesis by comparing the cortical sources of the 40 Hz auditory SSF with sources of the middle latency Pa wave which is prominent in electrical and magnetic recordings, and with the cortical sources of the familiar N1 wave, at different carrier frequencies between 250 and 4000 Hz. SSF sources determined for the different carrier frequencies were found to display a 'medial' tendency tonotopy resembling that of the N1m (sources for the higher frequencies represented more deeply within the supratemporal sulcus), opposite the 'lateral' tendency tonotopy of the middle latency Pam (sources for the higher frequencies situated more laterally). A medial SSF tonotopy was observed in each of the subjects investigated, including three subjects for whom Pam and N1m maps were also available. These findings suggest that the 40 Hz SSF may not consist of summated or entrained middle latency responses, as has previously been proposed. Alternative mechanisms for the SSR are discussed.

Binaural fusion and the representation of virtual pitch in the human auditory cortex

The auditory system derives the pitch of complex tones from the tone's harmonics. Research in psychoacoustics predicted that binaural fusion was an important feature of pitch processing. Based on neuromagnetic human data, the first neurophysiological confirmation of binaural fusion in hearing is presented. The centre of activation within the cortical tonotopic map corresponds to the location of the perceived pitch and not to the locations that are activated when the single frequency constituents are presented. This is also true when the different harmonics of a complex tone are presented dichotically. We conclude that the pitch processor includes binaural fusion to determine the particular pitch location which is activated in the auditory cortex.

The auditory evoked "off" response: sources and comparison with the "on" and the "sustained" responses

OBJECTIVE

It is well known that tone bursts elicit a prominent N1/P2 complex in the auditory evoked potential (the on-response), but less is known about a morphologically similar complex (the off-response) that can be recorded under suitable stimulus conditions. The interaction between the two responses indicated that the responses were not physiologically independent. The present experiment employed neuromagnetic methods to determine the cortical sources of N1 and P2 on- and off-responses and their relation to other events observed in the auditory evoked field.

DESIGN

Five female and five male subjects with no history of otologic or neurological disorders and with normal audiological status participated in this study. Tone bursts of 2 sec duration (10 msec rise and decay time, cosine function), carrier frequency of 1 kHz, and intensity of 60 dB nHL (normative hearing level) were presented 512 times to the subject's right ear (contralateral to the investigated hemisphere) with an interstimulus interval randomized between 5 and 7 sec.

RESULTS

The present study is unique in that several components of the complex auditory evoked response (P1, N1on, P2on, sustained-field, N1off, P2off) were recorded and localized in the same subjects and in the same experiment. The source coordinates obtained for N1 and P2 on- and off-responses indicated that the two responses are generated by overlapping cortical regions. Sources for the P2 components were situated anterior and medial to sources for the N1 components and were indistinguishable from sources for the auditory sustained-field. An early P1on event preceded the N1on (but not the N1off) response and was spatially indistinguishable from the N1on. The equivalent source strength was greater for N1on and P2on sources compared with N1off and P2off sources.

CONCLUSIONS

The recoding process signaled by on-and off-responses may be a dynamic form of plasticity in the auditory cortex with a time constant on the order of hundreds of milliseconds, corresponding to the duration of sustained-responses released by acoustic changes and to the duration of the acoustic foreperiod that is necessary before on-and off-responses to acoustic changes can be observed.

The neurotopography of vowels as mirrored by evoked magnetic field measurements

The auditory evoked neuromagnetic field elicited by synthetic specimens of the vowels [a], [ae], [u], and [i] was recorded over the left and the right hemisphere of 11 subjects. The N100m and the SF deflection of the recorded signal was submitted to equivalent current source analysis using the model of a single dipole in a spherical volume conductor. Vowel processing was hypothesized to occur in a multistage process rendering a sequence of representations of the acoustic input. Vowel representations were considered to differ among each other in the features they make salient, thus, in the kind of dissimilarity relationship they establish, and, by implication, in terms of the vowel space defined by the respective set of dissimilarities. It was investigated whether a mapping exists between at least one of a number of hypothetical vowel spaces and the cortical response space spanned by the spatial distribution of vowel evoked equivalent current dipoles. Although the spatial configuration of vowel evoked sources proved to be highly variable across subjects, the ordering of distances between N100m and SF equivalent current dipole locations turned out to correspond to the ordering of distances between the corners of a vowel trapezium. There were some, albeit weak, indications of hemispheric differences in vowel processing. The results suggest that the spatial distribution of the equivalent current dipole sources of both the N100m and the SF deflection of the neuromagnetic field elicited by vowels reflect a processing stage transitional between auditory and phonetic representation.

Neurophysiological correlate of the auditory after-image ('Zwicker tone')

The 'Zwicker tone' (ZT) is an auditory after-image that can be evoked most effectively when a band-suppressed noise (relative width of gap 1/3 octave) presented for a certain period of time has been switched off. The sensation of this purely monaural phenomenon is that of a pure tone with a frequency corresponding to the center frequency of the gap and an equivalent level of 10-15 dB above auditory threshold. The sensation decays gradually; it may last as long as 10 s depending on how long the evoking noise was presented. The search for a physiological correlate has been futile so far, probably because the search was confined to more peripheral levels of the auditory system (inferior colliculus). A neuromagnetic study was performed in normal-hearing subjects in order to look for a neurophysiological correlate of the ZT in the auditory cortex. With a stimulation paradigm especially designed for this study, we have been able to isolate poststimulus activity which appears to be related to the ZT and which originates in the supratemporal auditory cortex. It is a sustained neuromagnetic activity that shows a clear-cut dipolar field distribution, and it appears that this activity has certain similarities with the tone-evoked auditory sustained response. The hypothesis is put forward that during the sensation of the ZT a process takes place in the auditory cortex which is similar to that underlying the sustained response, and which gives rise to the sensation of the ZT. In contrast to the sustained response, however, which is due to neural activity evoked by an external acoustic stimulus, the sustained activity associated with the ZT is due to a temporary absolute or relative reduction of neural activity originating from those regions in which the ZT exciting stimulus caused an adaptation. These differences in neural activity cannot be distinguished by the auditory system from a corresponding external acoustic signal. Preliminary studies in patients suffering from tonal tinnitus yielded results which exhibit a certain similarity with those obtained in the ZT experiment.

Assisting students at risk: using computer NCLEX-RN review software

In response to a decline in the success rate on the National Council Licensure Examination for Registered Nurses (NCLEX-RN) examination, the authors developed a program to identify and assist students at risk for failure. The use of a computerized NCLEX-RN practice examination and an individualized student review and study process is described.

Magnetic imaging in human classical conditioning

Magnetoencephalography (MEG) was recorded during aversive classical conditioning in an attempt to elucidate the temporal coding of primary somatosensory cortex (SI) activation previously found with positron emission tomography. Four healthy volunteers participated in the experiment. The reinforced conditioned stimulus was displayed on a screen for 2 s, and as it disappeared an unconditioned electric shock to the right middle finger followed. A control stimulus, not paired with a shock was also presented. With MEG, we observed a conditioned magnetic response located in the SI. The conditioned response predated the shock presentation and is interpreted as evidence for functional control of nociception mediated by corticothalamic projections.

The value of abdominal exploration during cholecystectomy

With the advent of 'minimal access' cholecystectomy patients no longer have an exploratory laparotomy at the time of the operation and it is possible that relevant pathology may be missed as a result. This study analyses the findings at exploratory laparotomy in 223 patients undergoing open cholecystectomy. Forty-two patients (19%) were found to have incidental pathology but in only three (1.3%) did this lead to additional operative procedures. We therefore conclude that the loss of exploratory laparotomy at cholecystectomy does not have a significant detrimental effect on patient care.

Oral Candida albicans from patients infected with the human immunodeficiency virus and characterization of a genetically distinct subgroup of Candida albicans

Candida albicans has been shown to vary in its phenotypic expression with the progression of human immunodeficiency virus (HIV) infection. This study was designed to investigate whether in Category IV HIV infected patients (CDC, Atlanta, USA) these phenotypic changes were related to changes in the genetic strain of the organism. Isolates of C. albicans were obtained from 45 patients with HIV infection during the progression of their disease as determined by percentage T4 lymphocyte count. Isolates were strain differentiated using two methods. In 67 per cent of the patients a single strain of C. albicans, as determined by the DNA analysis, was isolated from each individual over the experimental period. The phenotypic expression of the genetically identical strains isolated from each patient varied considerably over the experimental period with the morphotype 754 being predominant. These results showed that the genotype of C. albicans isolated persisted in the majority of HIV infected individuals, but that the phenotypical expression of this strain changed. A finding in this study was that 18 strains of C. albicans had DNA which did not hybridize to the probe used. These strains were analysed for the presence of two other C. albicans specific DNA segments using PCR. The probe 27A hybridizing strains yielded PCR products which differed from the non-hybridizing strains. Five of these genetically atypical C. albicans strains and 98 of the C. albicans strains were then analysed for purported virulence factors.(ABSTRACT TRUNCATED AT 250 WORDS)

Characterization of genetically distinct subgroup of Candida albicans strains isolated from oral cavities of patients infected with human immunodeficiency virus

During the course of a study of oral Candida albicans strains from 60 human immunodeficiency virus-infected patients over a 2.5-year period, 18 of the 295 C. albicans isolates had genomes that failed to hybridize with a C. albicans-specific DNA probe (27A). These strains were germ tube positive and chlamydospore positive and were identified as C. albicans by the ID 32C test (API Systems, Montlieu, France). These strains were analyzed for the presence of two other C. albicans-specific DNA segments by PCR. The first was a C. albicans 1,348-bp species-specific sequence, and the second was a 1,059-bp C. albicans repetitive element. The probe 27A-hybridizing strains yielded PCR products which differed from those of the nonhybridizing strains. Five of these genetically atypical C. albicans strains and 98 of the C. albicans strains were then analyzed for purported virulence factors. The genetically atypical C. albicans strains, in comparison with typical C. albicans strains, produced greater amounts of extracellular proteinase (P = 0.038, Student's t test), adhered to a greater degree to buccal epithelial cells (P = 0.018, Student's t test), and were less susceptible to the antifungal drug 5-flucytosine (P = 0.0003, Mann-Whitney test). Analysis of these strains with other common antifungal drugs showed no statistically significant variation in susceptibility. The results of this study indicated that these genetically atypical C. albicans strains possess increased virulence in comparison with typical C. albicans strains.

Effects of piezoelectric lithotripsy on human DNA

Genomic DNA was extracted from excised gallbladder mucosa, obtained shortly after a single treatment piezoelectric lithotripsy. Control samples were obtained from age and sex-matched patients who had received no lithotripsy. No DNA fragmentation was demonstrable on agarose gel electrophoresis. Suspensions of cultured lymphoblasts were subjected to different shock wave doses and the percentage of cells surviving the treatment was assessed immediately and the rate of cell death monitored over the following 7 h. The proportion of cells surviving the treatment decreased with increasing shock wave doses, but subsequent rate of cell death was no different from controls. DNA, extracted from the intact surviving cells, again showed no evidence of fragmentation on electrophoresis, but the DNA extracted from the supernatant showed extensive fragmentation.

Effects of methylphenidate in HIV-related depression: a comparative trial with desipramine

This report is a randomized, double-blind, comparative trial of desipramine with the psychomotor stimulant methylphenidate. Twenty HIV antibody-positive patients with depressive symptoms were randomly assigned to either drug. After individual dose titration, the mean daily dose of desipramine was 150 mg. and methylphenidate 30 mg. daily. The differences in responses between desipramine and methylphenidate were not statistically significant on various measures of depression. The antidepressant effect of methylphenidate did not occur any faster than that of desipramine. Both significantly reduced depressive and anxious symptomatology over the blinded portion of the treatments. Thus, methylphenidate relieves depressive symptomatology with efficacy similar to that of desipramine, offering an alternative to patients who are unable to tolerate standard tricyclic antidepressant therapy. The dopaminergic effects of methylphenidate are likely to mediate its antidepressant effects.

Clinical applications of magnetic resonance spectroscopy

Neurospectroscopy measures a neuronal marker, energy and redox state, specific fuels of tissue respiration, maturation, and possibly myelination. It provides diagnostic patterns of altered neurochemistry. Current clinical uses range from intensive care in neonates to dementia in the elderly and include tumor and stroke management, prognosis in hemorrhage and trauma, white matter, inflammatory diseases, and AIDS. Inborn errors, metabolic and systemic diseases, subclinical hepatic encephalopathy, hyponatremia, and "coma" have been elucidated. Automation, single-voxel MRS, chemical shift imaging, quality control, and outcome analyses are discussed. With no remaining impediments to clinical use, neurospectroscopy has changed the way we look at diseases of the brain.

A 2'-O-thiol tether in the ribose moiety of nucleic acids for conjugation chemistry

A 2'-O-hexylthiotrityl adenosine phosphoramidite has been synthesized and incorporated into oligodeoxyribonucleotide (oligo) phosphodiesters and phosphorothioates. These oligos possess the lipophilic 2'-O-hexylthiotrityl group at pre-selected positions. Upon treatment with silver nitrate solution, a free thiol group was generated which was further functionalized. The new tether offers a convenient nucleophile for conjugation of various pendant moieties that would reside in the minor groove. Because of its versatility and location, the modification has a variety of potential applications, most notably as an enhancer of antisense activity.

Cost effectiveness of adjuvant bile salt treatment in extracorporeal shock wave lithotripsy for the treatment of gall bladder stones

The relative cost effectiveness of adjuvant urso and chenodeoxycholic acid treatment in extracorporeal shockwave lithotripsy (ESWL) has been assessed as part of a pragmatic randomised controlled trial of ESWL as a treatment of gall bladder stones. Of the first patients with gall stone volume < 4 cm3 randomised to ESWL in the main trial, 24 were randomised to have ESWL alone and 26 to have adjuvant bile acid treatment, one of whom died before the end of the 12 month follow up period. At 12 months after treatment, differences in gall stone clearance between ESWL alone (3/24 (13%) clear, 5 (21%) referred for surgery) and ESWL and bile acids (6/25 (24%) clear, 2 (8%) referred for surgery) were not significant (p = 0.36, log rank test). Patients in both groups had substantial and significant health gains (according to biliary pain frequency and severity, Nottingham Health Profile scores, visual analogue scale symptom scores, and complications) but there were no significant differences between the groups. Improvements in both groups usually occurred within a few weeks of treatment and were unrelated to gall stone clearance. Costs were greater in the bile salt group (95% confidence intervals for estimated cost difference: 90 pounds to 630 pounds). If the purpose of treatment is symptom relief rather than gall stone clearance then adjuvant bile salt treatment seems to be unnecessary.

Evaluation of intravenous ketorolac administered by bolus or infusion for treatment of postoperative pain. A double-blind, placebo-controlled, multicenter study

BACKGROUND

Ketorolac is a nonsteroidal analgesic that may provide postoperative analgesia without opioid-related side effects. This double-blind, randomized, multicenter study evaluated the analgesic efficacy and safety of intravenous ketorolac in 207 patients during the first 24 h after major surgery.

METHODS

Subjects were assigned to receive one of three analgesic regimens: a ketorolac infusion, ketorolac boluses, or placebo. All subjects had access to intravenous morphine via patient-controlled analgesia (PCA). Evaluations included PCA morphine used, pain assessment (categorical pain intensity scores and visual analogue pain scores), pain relief (categorical pain relief scores), sedation, presence of adverse events, and overall rating of regimens by study observers and patients.

RESULTS

Patients in the ketorolac infusion group (but not the ketorolac bolus group) used less morphine (average 33 mg) than did the placebo group (44 mg) (P = 0.009). Significant differences favoring both ketorolac groups were seen in the pain intensity and the categorical pain relief scores at various time points during the study. At the termination of the study, compared with the placebo group, categorical pain intensity scores were lower in the ketorolac bolus group; visual analogue pain scores were lower in both ketorolac groups; and pain relief scores were higher in the ketorolac bolus group. The incidence of vomiting was significantly greater in the placebo group (27%) than in the ketorolac infusion group (12%) or bolus group (9%) (P = 0.032 and P = 0.005, respectively). The incidence of postoperative fever was 10% in the ketorolac bolus group and 25% in the placebo group (P = 0.013). Study observers noted less nursing difficulty while caring for patients in the ketorolac infusion group (P = 0.015). Study observers and patients in both ketorolac groups reported statistically significant overall drug superiority compared with placebo.

CONCLUSIONS

It is concluded that intravenous boluses or infusions of ketorolac in conjunction with PCA morphine provide effective, safe analgesia after major surgery and improve on the response to PCA morphine alone.

A neuromagnetic study of the functional organization of the sensorimotor cortex

Movement-related neuromagnetic fields from eight healthy human subjects were investigated in a Bereitschaftspotential paradigm. The three conditions studied were right-sided mouth, index finger and foot movement. The neuromagnetic field patterns corresponding to the motor field and the movement-evoked field I were analysed using a moving dipole model. For both components a somatotopic organization was found: the estimated dipole locations for the mouth were more lateral and those for the foot more medial than the estimated dipole positions for the index finger movement. With regard to possible clinical applications, e.g. non-invasive mapping of the sensorimotor cortex and studies of plasticity of the motor function, the present results suggest that the investigation of movement-evoked field I for the index finger condition is most likely to yield further results.

Effects of post-mortem delay on high affinity forskolin binding sites and adenylate cyclase activity in rat and human striatum and cerebral cortex

High affinity [3H]forskolin binding was measured using quantitative autoradiography in the striatum and frontal cortex of rat and human brain. Forskolin binding in rat striatum (310.8 +/- 26.0 pmol/g mean +/- S.E.M.) was approximately 4 times that in the frontal cortex (75.5 +/- 8.4 pmol/g), whereas in post-mortem human brain each region exhibited similar levels of forskolin binding (striatum 51.3 +/- 1.2 and cortex 53.2 +/- 2.1 pmol/g). Basal adenylate cyclase activity was assayed in membranes prepared from striatum and frontal cortex of rat and human; enzyme activity in the rat striatum was approximately 2-fold that in rat frontal cortex whereas enzyme activity in the human striatum was similar to that in the human frontal cortex. To investigate the effect of the interval between death and freezing of the brain, rats were killed by decapitation, then maintained at 37 degrees C for up to 4 hours before freezing and subsequent assay of forskolin binding and adenylate cyclase activity. Striatal forskolin binding declined markedly post-mortem such that 4 h post-mortem it was only 13% of the level in control animals while levels of cortical forskolin binding declined minimally during the immediate post-mortem period. Striatal and cortical adenylate cyclase activity (basal) was minimally influenced by post-mortem delay although in both regions there was a rapid loss of the ability of fluoroaluminate to stimulate adenylate cyclase. The data suggest that the striatum contains a population of high affinity forskolin binding sites which is extremely sensitive to post-mortem delay.(ABSTRACT TRUNCATED AT 250 WORDS)

The Wilson disease gene is a copper transporting ATPase with homology to the Menkes disease gene

Wilson disease (WD) is an autosomal recessive disorder characterized by the toxic accumulation of copper in a number of organs, particularly the liver and brain. As shown in the accompanying paper, linkage disequilibrium & haplotype analysis confirmed the disease locus to a single marker interval at 13q14.3. Here we describe a partial cDNA clone (pWD) which maps to this region and shows a particular 76% amino acid homology to the Menkes disease gene, Mc1. The predicted functional properties of the pWD gene together with its strong homology to Mc1, genetic mapping data and identification of four independent disease-specific mutations, provide convincing evidence that pWD is the Wilson disease gene.