The AXS battery and "neurological fingerprints": meeting the challenge of individual differences in human brain/behavior relations.

A new test battery, the Auditory Cross-Section (AXS) Battery, offers a relatively inexpensive, noninvasive means of describing a "neurological fingerprint" for each individual. The battery's "access to axes" combines physiological and behavioral measures so that a large set of dependent variables can be used to profile an individual and can serve as a context for additional anatomical, behavioral, and physiological data for the same subject. Physiological tests included in the battery described here include (1) otoacoustic emissions (OAEs); (2) the repeated evoked potentials version of the auditory brainstem response (REPs/ABR); and (3) quantitative electroencephalography (qEEG). Complementary behavioral tests were chosen to assess capabilities related to functional asymmetries, such as phonemic awareness and fine motor control, and/or to demonstrate temporal correlations that link behavioral and neural function. Applications of the AXS battery include (1) documentation of individual differences and similarities in neural organization that are related to specific behaviors, such as learning styles or clinical symptoms; (2) provision of contextual data for neuroimaging studies that aid in interpreting individually specific patterns of activation; and (3) development of a neurotypology of human brain/behavior relations, linking characteristics of neuroanatomy and neurophysiology with features of behavior, and general body health.

The handshaking model of brain function: notes toward a theory.

John Hughlings Jackson described the system-level organization of the nervous system in terms of functional-control relations between neural centers. His model emphasized hierarchical organization along a rostral-caudal dimension, with applications primarily to cases of clinical disorders such as epilepsy and motor paralysis. This paper outlines a new systems-level model of brain function, updating Jackson's original idea to account for all three orientations of body/brain organization, and additional, non-hierarchical types of relations. The approach may provide a powerful tool for addressing many aspects of human brain and behavior, ranging from normal characteristics (such as individual differences and gender differences), to cases of frank neurological injury, to other conditions, such as hyperactivity and chronic pain, conventionally considered as 'neurologically silent'.

Physiological and behavioral effects of an antivertigo antihistamine in adults.

12 neurologically normal adults were tested before and after administration of meclizine, an over-the-counter medication for motion sickness. A battery of four tests was used: (1) distortion-product otoacoustic emissions, (2) the Repeated Evoked Potentials version of the Auditory Brainstem Response, (3) quantitative electroencephalography measured over the left and right sides of the auditory cortex, and (4) a hand-eye coordination task. The battery required approximately 1.5 hr. to complete. Each subject was tested with the battery in each of eight longitudinal sessions: three times on a control day (9 am, 1 pm, 3 pm--no medication); the same times on a second day one week later (medication at approximately 11:30 am), and 24- and 48-hr. check-up sessions following the medication day. Analysis indicated changes in all components, with details suggesting the site(s) of action of this type of antihistamine. The cross-section of the auditory system yielded by this battery makes it possible to observe effects at the periphery, in the brainstem, and in the cortex, including evidence linking otoacoustic emissions with central auditory physiology. Implications range from cautions regarding the use of antihistamines to physiological support for employing such medications to enhance patients' response to vestibular rehabilitation as well as to improve performance in learning-disordered children.

Neuroimaging and the trimodal brain: applications for developmental communication neuroscience.

New details generated by neuroimaging and other methods for studying the neural correlates of behavior have led to the formulation of a new model of brain organization, the Trimodal Brain. The model incorporates current biochemical; anatomical, and physiological concepts of prenatal brain growth and combines them with findings on right/left functional asymmetries. It provides a means of relating a wide range of human behaviors and clinical states according to a common base of neural organization, and stresses the utility of an organizational rather than a lesion model for understanding developmental communication disorders.

Amplitude stability of auditory brainstem responses in two groups of children compared with adults.

A recent report indicated that patterns of systematic variation may be observed in ABR peak latency of children from two age groups, and that comparisons of the children's latency data with similar findings in adults suggest new evidence for developmental changes in the human central auditory nervous system persisting as late as 12 years of age. The current report examines the stability of auditory brainstem response (ABR) peak amplitude for the same three groups of subjects, including: (1) across-age comparisons of absolute amplitude, between-subjects group stability, and within-subjects group stability; (2) documentation of individual differences in amplitude stability by peak and by ear; and (3) demonstration of the degree of replicability of amplitude stability patterns. Results indicate that the same observations are to made for ABR amplitude as for latency; that is, systematic patterns of stability at all three ages, with details that provide additional evidence for developmental changes in brainstem-mediated auditory electrophysiological response continuing into the second decade of life.

Latency stability of auditory brainstem responses in children aged 10-12 years compared with younger children and adults.

Previous articles have reported the results of using standard clinical procedures in our laboratory for testing auditory brainstem responses (ABR) in a repeated-measures design, in order to quantify ABR latency and amplitude stability in normal young adults. In a subsequent paper, these findings were extended to include the results of similar procedures in a group of seven children ranging in age from 5 to 7 years. The current experiment involves repeated-measures ABRs in a group of nine children ranging in age from 10 to 12 years. Results indicate that while these older children show the expected similarities with adults in terms of ABR peak latencies, their latency stability values are in some cases significantly lower than adults. At the same time, ABR stabilities measured in the older children show some differences compared to data from the younger children studied previously. For all groups, the same types of patterns are observed: (1) significant differences contrasting the degree of between-subject v. within-subject latency stability; (2) clear individual differences characterizing subjects; (3) within-subject distinctions according to ear of stimulation; and (4) instances of good replicability of the 'latency-stability profiles' calculated for one set of repeated waveforms v. a second set collected later in testing.

Processing asymmetries for complex sounds: comparisons between behavioral ear advantages and electrophysiological asymmetries based on quantitative electroencephalography.

This experiment extends our earlier work on individual differences in ear advantages for complex sounds (Lauter 1982, 1983, 1984) to examine the results of combined behavioral and qEEG testing in the same subjects. Results include: (1) between-subject differences in absolute values together with between-subject agreements in terms of relative values, observed both for ear advantages (EAs) and hemisphere advantages (HAs); (2) within-subject agreement between behavioral (EAs) and physiological (HAs) measures of asymmetries; and (3) preliminary findings related to the interpretation of qEEG asymmetry data, such as the influence of hand movements on auditory-cortex qEEG recordings, and persistence of activation effects in which asymmetries evoked during a stimulation condition may be reflected in resting asymmetries observed during a subsequent control condition.

Intrasubject variability in the absolute latency of the auditory brainstem response.

For many applications, the latency of obtained ABR peaks is compared to clinical norms. Using this approach, one presupposes that basic assumptions regarding inter- and intrasubject variability of latency are met. Although much is known about intersubject variability, virtually nothing has been reported about intrasubject variability. The purpose of this investigation was to describe intrasubject variability of ABR latency as observed in a clinical setting. Nine male subjects, 10 to 12 years old, participated in the study. At each of four sessions, five ABRs were obtained for each of three stimulus conditions. Stimuli were 100 microseconds condensation clicks presented at 80 dB nHL. For each ABR peak, the intrasubject distribution of latencies was analyzed. For every subject, variability of latency was observed. Typically, the latencies were normally distributed, and the magnitude of variability was less than is commonly reported for groups of subjects. We conclude that by establishing a baseline, the sensitivity of the ABR might be increased for certain monitoring applications.

Individual differences in auditory electric responses: comparisons of between-subject and within-subject variability. IV. Latency-variability comparisons in early, middle, and late responses.

In this series of reports to date (Lauter & Loomis, 1986, 1988; Lauter & Karzon, 1990 a & b) we have described patterns of relative variability observed in latency and amplitude of auditory brainstem responses (ABRs) collected in a repeated-measures within-subjects design testing two groups of neurologically normal adults. Each of the two groups of subjects was additionally tested for one other type of auditory evoked potential, according to the same schedule of eight weekly sessions: middle-latency responses (MLRs: 10 to 50 ms post-stimulus) were collected from Group II (four females and four males), and late responses (50 to 300 ms post-stimulus) from Group I (four females and three males). This paper presents data comparing and contrasting the patterns of relative variability of waveform-peak latency observed in middle-latency, late responses, and the ABR data previously reported. Results document a trimodal distribution of response latency variability, with ABR peak V in one category, characterized by high within-subject stability and low between-subject stability, ABR peaks II, III, and IV, together with MLR peak No in a second category, of intermediate within-subject stability, and a third category consisting of ABR peak I together with all auditory-evoked-potential (AEP) peaks subsequent to MLR peak No, in which consistency of peak latency calculated within subjects approaches the low level of consistency calculated across subjects.

Individual differences in auditory electric responses. III. A replication, with observations of individual vs. group characteristics.

In the first two reports in this series (Lauter & Loomis, 1986, 1988) we presented data on repeated-measures testing with auditory brainstem responses (ABRs) for a group of 7 normal young adults. In this paper, we report data for an additional group of 8 young adults, which replicate the patterns for both latency and amplitude stability observed in the first group, in spite of a number of procedural differences between the two studies. Examples are also presented from both groups illustrating the effects of individual-subject characteristics on group characteristics. Results indicate that ABR latency-variability patterns based on 8-week series are quite different from subject to subject, including individual peculiarities in the pattern of responses according to ear-of-presentation, and the detail of these differences may both contribute to and be obscured by the group within-subject calculations. In contrast, ABR amplitude-variability patterns are much more similar across individuals and ear-of-presentation, most often taking the form of a 'W-shaped' function, with greater consistency at peaks I, III, and V, compared with peaks II and IV.

Individual differences in auditory electric responses: comparisons of between-subject and within-subject variability. V. Amplitude-variability comparisons in early, middle, and late responses.

Each of two groups of adult subjects was tested under a repeated-measures design (Lauter & Loomis, 1986, 1988; Lauter & Karzon, 1990a, b) for ABRs and one other set of responses: middle-latency responses (MLRs: 10 to 50 ms post-stimulus) from Group II (four females and four males), and late responses (50 to 300 ms post-stimulus) from Group I (four females and three males). A companion paper (Lauter & Karzon, 1990b) presents data comparing and contrasting the patterns of relative variability of waveform-peak latency observed in middle-latency, late responses, and the ABR data previously reported. This paper presents amplitude results for the same data sets. Our findings indicate that, as we have reported previously, with regard to between-subject vs. within-subject variability of peak parameters of auditory EP waveforms, normal adult subjects are more consistent when compared with themselves than when compared with each other. This is true at all auditory EP levels tested, from brainstem to cortex, and is observed in both amplitude and latency data, in spite of the fact that the actual values of amplitude-stability measures are an order of magnitude smaller than for latency stability.

Individual differences in auditory electric responses: comparisons of between-subject and within-subject variability. II. Amplitude of brainstem Vertex-positive peaks.

Recently, we (Lauter & Loomis, 1986) reported variability measures of the latency of five vertex-positive auditory brainstem response (ABR) peaks collected under a repeated-measures experimental design. Seven subjects were tested, each on eight separate sessions, for brainstem auditory evoked response to monaural right, monaural left, and binaural stimulus presentation. This paper presents variability measures for amplitudes of the same series of responses. Three types of variability measurement were made: 1) amplitude of each peak of the response to monaural right, monaural left, and binaural stimulation; 2) amplitude difference for each peak comparing binaural with right, and binaural with left; and 3) amplitude difference comparing binaural with the sum of the amplitudes of the two monaural responses. As in the previous report, between-subject variability and within-subject variability were expressed using a ratio of mean divided by standard deviation (this is the reciprocal of Pearson's Coefficient of Variation, and will here be referred to as the Coefficient of Stability, or Cs). For all amplitude comparisons, Cs profiles indicate that: 1) within-subject stability (i.e., consistency) is significantly greater than between-subject stability, 2) both within- and between-subject stability measures are sensitive to both peak and ear of presentation, and 3) stability profiles for individual subjects show individual differences and similarities, and are replicable over time. The variability measure also provides evidence of an ear asymmetry at peak III which has been noted in other ABR studies.

Individual differences in auditory electric responses: comparisons of between-subject and within-subject variability. I. Absolute latencies of brainstem vertex-positive peaks.

Seven subjects were tested, each on eight separate sessions, for brainstem auditory evoked responses to monaural right, monaural left, and binaural stimulus presentations. Comparisons of between-subject vs. within-subject variability of the absolute latencies of vertex-positive peaks expressed in terms of the coefficient of variation indicate that: within-subject stability is greater than between-subject stability for the five brainstem peaks; between-subject variability shows significant differences due to peak but not to ear of presentation; within-subject variability shows significant differences due to both peak and ear; comparisons of within-subject variability over time show significant differences due to peak but not to time; patterns of individual variation within the brainstem series are characterized by increases in stability of peak latencies over time, and by replicability of stability profiles over time. Other measures of latency and amplitude based on this series of responses are planned for a subsequent report.

Tonotopic organization in human auditory cortex revealed by positron emission tomography.

Positron emission tomography (PET) was used to map alterations in local neuronal activity induced in human primary auditory cortex by pure-tone stimulation. Patterns of blood flow were observed in specific regions on the superior temporal plane showing systematic changes in activity depending on the frequency of a stimulating pure tone. The orientation of these regions agrees well with data for non-human primates.

Hypnosis and its effects on left and right hemisphere activity.

Recent research suggests a relationship between hypnosis and the right cerebral hemisphere in man. With several major modifications in the 1978 study of Frumkin, Ripley, and Cox, the following hypothesis was investigated: Hypnosis creates a shift towards relatively greater left ear accuracy, suggesting greater participation of the right hemisphere during a trance. Two studies were undertaken with 36 right-handed male volunteers in each; 12 of low susceptibility to hypnosis, 12 of medium susceptibility, and 12 of high susceptibility. Study 1 investigated the affect hypnosis had on the processing of musical stimuli while Study 2 investigated its affects on verbal stimuli. Study 1 found that the more susceptible an individual was to hypnosis the greater the shift towards the left ear. Study 2 found no such relationship. Possible differences in stimulus characteristics which might have caused these different results were discussed.

Contralateral interference and ear advantages for identification of three-element patterns.

Recent experience with attempts to test relatively simple patterns such as three-tone sequences in a traditional dichotic-listening paradigm indicates that when such sequences are used for both target and contralateral interference, performance tends to be low in both ears and not useful for measuring or comparing ear advantages in various target conditions. It is reported that tests with a variety of sounds presented contralaterally to three-element patterns show that several such sounds can (1) allow performance in at least one ear to remain above floor values, (2) result in performance in at least one ear that is below ceiling, and (3) reveal ear advantages that are similar in direction and magnitude to those seen with the traditional dichotic paradigm.

Dichotic identification of complex sounds: absolute and relative ear advantages.

Dichotic identification of a variety of complex sounds was studied in seven listeners. Analysis of individual listeners' scores shows that there are significant individual differences in terms of absolute ear advantage for a given sound, while comparison of such differences across stimuli reveals agreements among individuals as to relative ear advantages, when both magnitude and direction of ear differences are considered. This agreement can be expressed in terms of a "relative ear advantage continuum." The experiments also indicated that ear advantages can show good reliability over as much as six months' time.