Neurology, technology, and the diagnostic imperative.

Advancements in diagnostic technologies have revolutionized the field of neurology. The use of these tools in the course of neurological evaluations is driven by a strong version of the diagnostic imperative, with the goal of precisely identifying the locus and extent of disease processes. Because of the discrepancy between the sophistication of these technologies and the availability of therapeutic interventions, there is active debate regarding the appropriate use of these tools when the diagnosis is clear, or when no change is made to the therapeutic management. A narrow view of management that is bounded by the availability of pharmacological or surgical interventions results in a more rigid dichotomy between the needs of doctors and patients. A broader view that relaxes the constraint between diagnostic procedures and interventions is more in keeping with the observation that many acts are performed for the benefit of doctors and patients alike. An historical and ethical analysis of the diagnostic imperative, with attention to the rise of innovative medical technologies and current concepts of therapeutic intervention, can help clarify the principles of medical paternalism and beneficence that guide current models of decision making in the neurological sciences.

Heinrich Klüver and the temporal lobe syndrome.

Heinrich Klüver and Paul Bucy described a constellation of symptoms in monkeys following large resections of the temporal lobe that they termed the "temporal lobe syndrome"; now commonly referred to as the Klüver-Bucy syndrome. The aim of this paper is threefold: (1) to review Heinrich Kluver's behavioral studies on monkeys that led up to his temporal lobe experiments with Paul Bucy; (2) to understand why Brown and Schäfer dismissed the behavioral changes in temporal lobe monkeys they had observed fifty years prior to the studies of Klüver and Bucy; and (3) to show that Klüver's phenomenologically motivated conceptual paradigm helped to unify both neuropsychological and neuroanatomical theories regarding the visual and emotive functions of the non-human primate temporal lobe.

How do monkeys look at faces?

Facial displays are an important form of social communication in nonhuman primates. Clues to the information conveyed by faces are the temporal and spatial characteristics of ocular viewing patterns to facial images. The present study compares viewing patterns of four rhesus monkeys (Macaca mulatta) to a set of 1- and 3-sec video segments of conspecific facial displays, which included open-mouth threat, lip-smack, yawn, fear-grimace, and neutral profile. Both static and dynamic video images were used. Static human faces displaying open-mouth threat, smile, and neutral gestures were also presented. Eye position was recorded with a surgically implanted eye-coil. The relative perceptual salience of the eyes, the midface, and the mouth across different expressive gestures was determined by analyzing the number of eye movements associated with each feature during static and dynamic presentations. The results indicate that motion does not significantly affect the viewing patterns to expressive facial displays, and when given a choice, monkeys spend a relatively large amount of time inspecting the face, especially the eyes, as opposed to areas surrounding the face. The expressive nature of the facial display also affected viewing patterns in that threatening and fear-related displays evoked a pattern of viewing that differed from that recorded during the presentation of submissive-related facial displays. From these results we conclude that (1) the most important determinant of the visual inspection patterns of faces is the constellation of physiognomic features and their configuration, but not facial motion, (2) the eyes are generally the most salient facial feature, and (3) the agonistic or affiliative dimension of an expressive facial display can be delineated on the basis of viewing patterns.

In vivo microelectrode localization in the brain of the alert monkey: a combined radiographic and magnetic resonance imaging approach.

A technique is described for in vivo localization of microelectrodes during single-unit recording in the alert monkey. Four hollow glass spheres filled with copper sulfate and iohexol were affixed to the surface of the animal's skull prior to the acquisition of a series of coronal magnetic resonance (MR) images. These reference beads were visible in both X-ray and MR images. Cranial recording chambers were then implanted bilaterally over the amygdaloid complex. A microelectrode was advanced to various depths in the subject's brain. At each selected microelectrode site, five radiographs were obtained and a small electrolytic lesion was made. Based on the data from the radiographs, we computed the position of the microelectrode tip at each site relative to the reference beads. With a precision of 625 microns, this method was used to predict the neuroanatomical location of ten microlesions placed in both subcortical and cortical structures. Postmortem histological analysis revealed that the actual location of the lesions closely matched predictions arrived at using the X-ray/MRI localization technique. This technique thus provides an accurate, reliable and noninvasive method for in vivo localization of microelectrode recording sites.

Cross-modal associations and the human amygdala.

The role of the human amygdala in cross-modal associations was investigated in two subjects: SM-046, who had bilateral damage circumscribed to the amygdala; and the patient known as Boswell, whose damage in both temporal lobes includes the amygdala and surrounding cortices. Neither subject was impaired on Tactile-Visual or Visual-Tactile cross-modal tasks using the Arc-Circle test, suggesting that the amygdala is not involved in cross-modal associations involving perceptually "equivalent" basic stimulus properties. On the other hand, the results are compatible with the amygdala's involvement in higher-order associations between exteroceptive sensory data and interoceptive data concerned with correlated somatic states.

Event-related potentials in the retina and optic tectum of fish.

1. Compound field potentials were recorded with up to 18 microelectrodes in comb, brush, or spear arrays on and in the optic tectum and with suction electrodes from the distal stump of the cut optic nerve and from the optic nerve head in the opened eye in elasmobranchs and teleosts. Diffuse light flashes of different durations and submaximal intensities were delivered in trains with regular or irregular interstimulus intervals (ISI). 2. Event-related potentials (ERPs) are visible in single trials and begin at 50-200 ms after an "oddball" flash, especially one that is slightly weaker, briefer, or delayed by as little as 6% of ISI, compared with the more frequent stimulus. ERPs to the opposite condition are not of the same form or size. 3. One or more stimuli were omitted from a train or the train terminated after various conditioning times. Deflections occur beyond the expected visual-evoked potentials (VEPs) to the last flash and are called omitted-stimulus potentials (OSPs). They occur on schedule--approximately 100 ms after the next flash would be due--almost independent of intensity, duration, or conditioning time. They are considered to be ERPs without any necessary implication or denial of a temporally specific expectation. 4. Three components of OSP occur alone or in combination: an initial fast peak, a slow wave, and an oscillatory spindle up to ls or more in duration. This resembles the OFF response to steady light. 5. All these components are already present in the retina with optic nerve cut. 6. The same mean ISI with a high proportion of jitter gives OSPs with only slightly longer latencies and smaller amplitudes; the OSP acts as though the retina makes an integrated prediction of ISI, intensity, and duration. 7. During a conditioning train the equilibrium between excitation and inhibition after each flash changes according to frequency, intensity, duration, and conditioning time; the VEP reflects this in a shape unique to the ISI; inhibition increases rapidly after each flash and then decays slowly according to the recent mean ISI. This allows rebound disinhibition after missing, weak, or delayed flashes (OSP or ERP) or causes an altered VEP after a longer or stronger oddball. 8. It seems unlikely that the OSP or oddball ERP in fish tectum is equivalent to mammalian ERPs under the same regime or signals higher cognitive events, because they are already present in the retina, require flash frequencies greater than 1 Hz, and grow with frequency up to and beyond flicker fusion.(ABSTRACT TRUNCATED AT 400 WORDS)

Dynamic properties of visual evoked potentials in the tectum of cartilaginous and bony fishes, with neuroethological implications.

We have extended the study of Bullock ('84), who reported on visually evoked potentials (VEP) in the tectum of 10 species of elasmobranchs, by adding further stimulus regimes, multichannel recording, and additional taxa, particularly addressing the question of flicker fusion frequency by electrophysiological signs in central processing centers. Using principally the guitarfish, Platyrhinoidis and Rhinobatos, and the bass, Paralabrax, with some additional data from 32 other species, the findings support the following conclusions: 1. Latency of the first main VEP peak, a sharp surface negativity, to a diffuse white flash of submaximal intensity while the eye is moderately light adapted varies from less than 20 ms in some teleosts to greater than 120 ms in agnathans, holocephalans, and some rays. Among the elasmobranchs tested, the sharks are generally faster than the rays. Among the teleosts tested, some species are at least three times slower than others. There is little overlap between the fastest elasmobranchs and the slowest teleosts. 2. After the first VEP peak, later components are more diverse than the classic descriptions of one late surface-negative hump; they may include also sharp peaks, slow humps, and oscillatory waves extending out to greater than 1 s postflash. These are highly labile, variable and similar to OFF responses after a long light pulse. All these components occur already in the retina, whether the optic nerve is intact or cut. Many records do not show the late components; in the same preparation, some tectal loci may and others may not. 3. Ongoing activity (the micro-EEG, over all frequency bands) is depressed between early and late waves after a flash as well as during a long light pulse. 4. Repeated flashes above a few per second do not so much cause fatigue of the VEPs as reduce or prevent them by a sustained inhibition; large late waves are released as a rebound excitation any time the train of flashes stops or is delayed or sufficiently weakened. 5. Repeated flashes depress first the early waves; later waves follow 1:1 up to an upper following frequency (UFF) of approximately 13 Hz in the guitarfishes at optimal intensity and light adaptation (15-17 degrees C). A transition zone of gradual fusion from 15 to 30 Hz is marked by sputtering or irregular sharp VEPs; above a lower fusion frequency (LFF) of 30-40 Hz, the flash train becomes equivalent to steady light.(ABSTRACT TRUNCATED AT 400 WORDS)