Start | basic neuroanat. | reading | zeki extracts | table of links | List of Refs | Journals
Albright, T. D., Kandel, E. R., & Posner, M. I. (2000). Cognitive neuroscience. Current Opinion in Neurobiology, 10(5), 612-624.
The last decade of the 20th century has seen the development of cognitive neuroscience as an effort to understand how the brain represents mental events. We review the areas of emotional and motor memory, vision, and higher mental processes as examples of this new understanding. Progress in all of these areas has been swift and impressive, but much needs to be done to reveal the mechanisms of cognition at the local circuit and molecular levels. This work will require new methods for controlling gene expression in higher animals and in studying the interactions between neurons at multiple levels.
Fletcher, P. C., & Henson, R. N. A. (2001). Frontal lobes and human memory - Insights from functional neuroimaging. Brain, 124, 849-881.
The new functional neuroimaging techniques, PET and functional MRI (fMRI), offer sufficient experimental flexibility and spatial resolution to explore the functional neuroanatomical bases of different memory stages and processes. They have had a particular impact on our understanding of the role of the frontal cortex in memory processing. We review the insights that have been gained, and attempt a synthesis of the findings from functional imaging studies of working memory, encoding in episodic memory and retrieval from episodic memory. Though these different aspects of memory have usually been studied in isolation, we suggest that there is sufficient convergence with respect to frontal activations to make such a synthesis worthwhile. We concentrate in particular on three regions of the lateral frontal cortex-ventro-lateral, dorsolateral and anterior-that are consistently activated in these studies, and attribute these activations to the updating/maintenance of information, the selection/manipulation/monitoring of that information, and the selection of processes/subgoals, respectively. We also acknowledge a number of empirical inconsistencies associated with this synthesis, and suggest possible reasons for these. More generally, we predict that the resolution of questions concerning the functional neuroanatomical subdivisions of the frontal cortex will ultimately depend on a fuller cognitive psychological fractionation of memory control processes, an enterprise that will be guided and tested by experimentation. We expect that the neuroimaging techniques will provide an important part of this enterprise.
Goel, V., & Dolan, R. J. (2001). The functional anatomy of humor: segregating cognitive and affective components. Nature Neuroscience, 4(3), 237-238.
Humor, a unique human characteristic, is critical in thought, com-munication and social interaction. Successful jokes involve a cogni-tive juxtaposition of mental sets, followed by an affective feeling of amusement; we isolated these two components of humor by using event-related fMRI on subjects who listened to auditorily present-ed semantic and phonological jokes (puns) and indicated whether or not they found the items amusing. Our findings suggest that where-as there are modality-specific pathways for processing the juxtapo-sition of mental sets necessary for the appreciation of jokes, a common component of humor is expressed in activity in medial ventral prefrontal cortex, a region involved in reward processing.
Goetz, C. G. (2000). Battle of the titans - Charcot and Brown-Sequard on cerebral localization. Neurology, 54(9), 1840-1847.
Objective: To examine the differing views of Jean-Martin Charcot and Charles Edouard Brown-Sequard-two celebrated neuroscientists of the nineteenth century-on cerebral localization as exemplified in their controversial debate of 1875 at the Societe de Biologie in Paris. Background: As clinicopathologic correlations were developed in the mid and late nineteenth century, cerebral localization was a primary topic of debate at scientific, social, and religious levels. Charcot, representing an anatomic approach to research, and Brown-Sequard, representing a physiologic perspective, disagreed fundamentally on the importance of cerebral localization to normal behavior and neurologic illness. Methods: The minutes of the Societe de Biologie meetings of 1875 and 1876, as well as primary archive documents from the Archives Nationales de 1'Academie des Sciences and the Bibliotheque Charcot, were examined. Results: Charcot was a strong proponent of localization theory and relied on human pathologic material primarily from isolated cerebral hematomas to establish the role of the cortex and subcortical white matter fiber tracts to motor and sensory function. Brown- Sequard used his animal physiology experiments to argue that; the brain was composed of complex networks and that isolated lesions had no direct bearing on the localization of cerebral function. Conclusion: Although Charcot's simple and direct anatomic methods won the debate on this occasion, Brown- Sequard's prioritization of physiology and experimentalism became beacons of modern neurologic study at the close of the nineteenth century. Charcot's later failures in the study of hysteria can be viewed as attempts to mimic physiologic experiments in the manner of Brown-Sequard's scientific methods.
Gould, E., Reeves, A. J., Fallah, M., Tanapat, P., Gross, C. G., & Fuchs, E. (1999). Hippocampal neurogenesis in adult Old World primates. Proceedings of the National Academy of Sciences of the United States of America, 96(9), 5263-5267.
The production of new hippocampal neurons in adulthood has been well documented in rodents. Recent studies have extended these findings to other mammalian species, such as tree shrews and marmoset monkeys. However, hippocampal neurogenesis has not been demonstrated in adult Old World primates. To investigate this possibility, we injected 11 adult Old World monkeys of different ages (5-23 years) with the thymidine analog bromodeoxyuridine and examined the fate of the labeled cells at different survival times by using neuronal and glial markers, In the young-adult and middle-aged monkeys, we found a substantial number of cells that incorporated bromodeoxyuridine and exhibited morphological and biochemical characteristics of immature and mature neurons. New cells located in the dentate gyrus expressed a marker of immature granule neurons, Turned On After Division 64 kDa protein, as well as markers of mature granule neurons including neuron specific enolase, neuronal nuclei, and the calcium-binding protein calbindin, Fewer new cells expressed the astroglial marker glial fibrillary acidic protein. Evidence of neurogenesis was observed in the oldest monkeys (23 years) as well, but it appeared to be less robust. These results indicate that the adult brains of Old World monkeys produce new hippocampal neurons, Adult macaque monkeys may provide a useful primate model for studying the functional significance of adult neurogenesis.
Gould, E., Reeves, A. J., Graziano, M. S. A., & Gross, C. G. (1999). Neurogenesis in the neocortex of adult primates. Science, 286(5439), 548-552.
In primates, prefrontal, inferior temporal, and posterior parietal cortex are important for cognitive function. It is shown that in adult macaques, new neurons are added to these three neocortical association areas, but not to a primary sensory area (striate cortex). The new neurons appeared to originate in the subventricular zone and to migrate through the white matter to the neocortex, where they extended axons, These new neurons, which are continually added in adulthood, may play a role in the functions of association neocortex.
Gross, C. G. (2000). Neurogenesis in the adult brain: death of a dogma. Nature Reviews Neuroscience, 1(1), 67-73.
For over 100 years a central assumption in the field of neuroscience has been that new neurons are not added to the adult mammalian brain. This perspective examines the origins of this dogma, its perseverance in the face of contradictory evidence, and its final collapse. The acceptance of adult neurogenesis may be part of a contemporary paradigm shift in our View of the plasticity and stability of the adult brain.
Grouios, G., Alevriadou, A., & Koidou, I. (2001). Weight-discrimination sensitivity in congenitally blind and sighted adults. Journal of Visual Impairment & Blindness, 95(1), 30-39.
This study compared the weight-discrimination sensitivity of 41 congenitally blind and 41 normally sighted adults. The superior weight-discrimination sensitivity of the congenitally blind subjects suggests that blindness from birth can cause compensatory adaptations within the cutaneous modality.
Hallett, M. (2001). Brain plasticity and recovery from hemiplegia. Journal of Medical Speech-Language Pathology, 9(2), 107-115.
The brain is capable of considerable reorganization even in adult life. This has been extensively studied in the motor system and can be demonstrated in a number of situations including deafferentation of a body part (such as in an amputation) and motor learning. Techniques including neuroimaging and transcranial magnetic stimulation (TMS) can be used to demonstrate this plasticity by mapping representations in the brain; TMS can also be useful in assessing excitability and briefly deactivating brain regions. With brain lesions such as stroke there can be considerable spontaneous recovery, and this appears to be due to plastic changes. Some recovery may be mediated by enhanced activity in ipsilateral pathways, and this is most clear in the recovery of swallowing. The best recovery of the upper extremity after stroke, however, is due to reorganization of the lesioned hemisphere. Rehabilitative strategies might well be able to enhance rehabilitative efforts.
Hamzei, F., Liepert, J., Dettmers, C., Adler, T., Kiebel, S., Rijntjes, M., & Weiller, C. (2001). Structural and functional cortical abnormalities after upper limb amputation during childhood. Neuroreport, 12(5), 957-962.
Functional reorganization has been well documented in the human adult brain after amputation of the arm. To assess the effects of amputation on the developing brain, we investigated six patients with upper limb amputation in early childhood and one with right dysmelia. Transcranial magnetic stimulation indicated contralateral cortical disinhibition and enlargement of the excitable area of the stump. FMRI data corroborated these plastic changes and also showed an ipsilateral functional reorganization. In the T1-weighted MRI, we found structural deformities of the contralateral and ipsilateral central sulcus in three patients and a contralateral atrophic parietal lobule in two patients. Therefore, arm amputation in childhood affects functional organization as well as anatomical structure in both hemispheres. NeuroReport 12:957-962 (C) 2001 Lippincott Williams & Wilkins.
Harris, J. A., Harris, I. M., & Diamond, M. E. (2001). The topography of tactile learning in humans. Journal of Neuroscience, 21(3), 1056-1061.
The spatial distribution of learned information within a sensory system can shed light on the brain mechanisms of sensory-perceptual learning. It has been argued that tactile memories are stored within a somatotopic framework in monkeys and rats but within a widely distributed network in humans. We have performed experiments to reexamine the spread of tactile learning across the fingertips. In all experiments, subjects were trained to use one fingertip to discriminate between two stimuli. Experiment 1 required identification of vibration frequency, experiment 2 punctate pressure, and experiment 3 surface roughness. After learning to identify the stimuli reliably, subjects were tested with the trained fingertip, its first and second neighbors on the same hand, and the three corresponding fingertips on the opposite hand. As expected, for all stimulus types, subjects showed retention of learning with the trained fingertip. However, the transfer beyond the trained fingertip varied according to the stimulus type. For vibration, learning did not transfer to other fingertips. For both pressure and roughness stimuli, there was limited transfer, dictated by topographic distance; subjects performed well with the first neighbor of the trained finger and with the finger symmetrically opposite the trained one. These results indicate that tactile learning is organized within a somatotopic framework, reconciling the findings in humans with those in other species. The differential distribution of tactile memory according to stimulus type suggests that the information is stored in stimulus-specific somatosensory cortical fields, each characterized by a unique receptive field organization, feature selectivity, and callosal connectivity.
Hastings, N. B., Tanapat, P., & Gould, E. (2000). Comparative views of adult neurogenesis. Neuroscientist, 6(5), 315-325.
Traditional views maintain that the generation of neurons within the mammalian brain is restricted to a discrete developmental period. This perspective has undergone significant revision during the later half of this century, culminating recently with the demonstration of neurogenesis in the brains of adult primates, including humans. Although it is becoming increasingly clear that adult neurogenesis represents an important mode of structural modification for the adult brain, its functional significance has not been determined. The production and survival of new neurons in the adult mammalian brain is regulated by both experiential and neuroendocrine factors, suggesting that adult-generated neurons may serve as a substrate by which these cues influence normal brain function. This article review significant advances that have led to the discovery of neurogenesis in adult mammals and examines comparative data suggesting that adult neurogenesis may play a role in certain forms of learning. Neural activity associated with behavioral experience is known to result in changes in brain structure and connectivity, for example, by modifying synapse number, axonal sprouting, dendrite length and branching, or synaptic strength. In the case of adult neurogenesis, experience may shape neural networks by directing the production and connectivity of whole cell populations.
Karl, A., Birbaumer, N., Lutzenberger, W., Cohen, L. G., & Flor, H. (2001). Reorganization of motor and somatosensory cortex in upper extremity amputees with phantom limb pain. Journal of Neuroscience, 21(10), 3609-3618.
Phantom limb pain (PLP) in amputees is associated with reorganizational changes in the somatosensory system. To investigate the relationship between somatosensory and motor reorganization and phantom limb pain, we used focal transcranial magnetic stimulation (TMS) of the motor cortex and neuroelectric source imaging of the somatosensory cortex (SI) in patients with and without phantom limb pain. For transcranial magnetic stimulation, recordings were made bilaterally from the biceps brachii, zygomaticus, and depressor labii inferioris muscles. Neuroelectric source imaging of the EEG was obtained after somatosensory stimulation of the skin overlying face and hand. Patients with phantom limb pain had larger motor- evoked potentials from the biceps brachii, and the map of outputs was larger for muscles on the amputated side compared with the intact side. The optimal scalp positions for stimulation of the zygomaticus and depressor labii inferioris muscles were displaced significantly more medially (toward the missing hand representation) in patients with phantom limb pain only. Neuroelectric source imaging revealed a similar medial displacement of the dipole center for face stimulation in patients with phantom limb pain. There was a high correlation between the magnitude of the shift of the cortical representation of the mouth into the hand area in motor and somatosensory cortex and phantom limb pain. These results show enhanced plasticity in both the motor and somatosensory domains in amputees with phantom limb pain.
Knecht, S., Drager, B., Floel, A., Lohmann, H., Breitenstein, C., Deppe, M., Henningsen, H., & Ringelstein, E. B. (2001). Behavioural relevance of atypical language lateralization in healthy subjects. Brain, 124, 1657-1665.
In most humans, language is lateralized to the left side of the brain. It has been speculated that this hemispheric specialization is a prerequisite for the full realization of linguistic potential. Using standardized questionnaires and performance measures, we attempted to determine if there are behavioural correlates of atypical, i.e. right-hemispheric and bilateral, language lateralization. The side and degree of language lateralization were determined by measuring the hemispheric perfusion differences by functional transcranial Doppler ultrasonography during a word generation task in healthy volunteers. Subjects with left (n = 264), bilateral (n = 31) or right (n = 31) hemisphere language representation did not differ significantly with respect to mastery of foreign languages, academic achievement, artistic talents, verbal fluency or (as assessed in a representative subgroup) in intelligence or speed of linguistic processing. These findings suggest that atypical hemispheric specialization for language, i.e. right- hemisphere or bilateral specialization, is not associated with major impairments of linguistic faculties in otherwise healthy subjects.
Martin, S. J., & Morris, R. G. M. (2001). Cortical plasticity: It's all the range! Current Biology, 11(2), R57-R59.
When rats learn a motor skill, synaptic potentials in the motor cortex are enhanced. A new study has revealed that this learning- induced enhancement limits further synaptic potentiation, but not synaptic depression. These findings support the view that activity- dependent synaptic plasticity is the brain's memory mechanism.
Nicolelis, M. A. L. (2001). Actions from thoughts. Nature, 409(6818), 403-407.
Real-time direct interfaces between the brain and electronic and mechanical devices could one day be used to restore sensory and motor functions lost through injury or disease. Hybrid brain-machine interfaces also have the potential to enhance our perceptual, motor and cognitive capabilities by revolutionizing the way we use computers and interact with remote environments.
Pallas, S. L. (2001). Intrinsic and extrinsic factors that shape neocortical specification. Trends in Neurosciences, 24(7), 417-423.
Increasing evidence points to the importance of intrinsic molecular cues in specifying the regional identity of mammalian neocortex. Few such cues, however, have been found to be restricted to individual functionally defined cortical areas before the arrival of afferent information. In contrast, thalamocortical axons are specifically targeted to individual cortical areas, raising the possibility that they can instruct some aspects of cortical areal identity. Cortical structure and function can be altered by modifying the source or pattern of activity in thalamocortical afferents. In particular, studies of crossmodal plasticity have shown that in many respects, one sensory cortical area can substitute far another after a switch of input modality during development. Afferent inputs might therefore direct the formation of their own processing circuitry, a possibility that has important implications for brain development, plasticity and evolution.
Pearson, P. P., Arnold, P. B., Oladehin, A., Li, C. X., & Waters, R. S. (2001). Large-scale cortical reorganization following forelimb deafferentation in rat does not involve plasticity of intracortical connections. Experimental Brain Research, 138(1), 8-25.
Physiological mapping of the body representation 1 month or longer after forelimb removal in adult rats revealed new pockets of shoulder representation in the forepaw barrel subfield (FBS) in the first somatosensory cortex (SI). These "new" shoulder representations have longer evoked response latencies than sites in the shoulder representation within the trunk subfield, hereafter referred to as the "original" shoulder representation. We postulated that the "new" shoulder representations in the FBS were relayed from the "original" shoulder representation. We investigated this: hypothesis by studying anatomical connectivity between the "original" shoulder representation and the FBS in intact control and forelimb deafferented adult rats using Phaseolus vulgaris leucoagglutinin (PHA- L), biocytin, and biotin dextran-amine (BDA) as anterograde tracers. The retrograde tracer cholera toxin beta subunit (CT-B) injected into the FBS was also used to study connectivity between the "original" shoulder representation and the FBS. Using these anatomical tracing techniques, we were unable to show the existence of a direct corticocortical connection between the "original" shoulder representation in the trunk subfield and the FBS in either intact or deafferented rats. Functional connectivity between the two cortical regions was studied by ablating the "original" shoulder representation alone or in combination with the shoulder representation in the second somatosensory cortex (SII) while recording evoked responses in the FBS following electrical stimulation of the shoulder. Both ablations failed to eliminate the evoked responses at the "new" shoulder sites in the FBS, suggesting that SI and SII are not necessary for "new" shoulder input in the FBS. It is suggested that subcortical sites may play a major role in large-scale cortical reorganization. Results of projections from the "original" shoulder representation to parietal medial (PM), parietal lateral (PL), SII, parietal ventral(PV), and parietal rhinal (PR) sensory fields and agranular lateral (AgL) and agranular medial (AgM) motor fields are also described.
Petitto, L. A., Zatorre, R. J., Gauna, K., Nikelski, E. J., Dostie, D., & Evans, A. C. (2000). Speech-like cerebral activity in profoundly deaf people processing signed languages: Implications for the neural basis of human language. Proceedings of the National Academy of Sciences of the United States of America, 97(25), 13961- 13966.
For more than a century we have understood that our brain's left hemisphere is the primary site for processing language, yet why this is so has remained more elusive. Using positron emission tomography, we report cerebral blood flow activity in profoundly deaf signers processing specific aspects of sign language in key brain sites widely assumed to be unimodal speech or sound processing areas: the left inferior frontal cortex when signers produced meaningful signs, and the planum temporale bilaterally when they viewed signs or meaningless parts of signs (sign-phonetic and syllabic units). Contrary to prevailing wisdom, the planum temporale may not be exclusively dedicated to processing speech sounds, but may be specialized for processing more abstract properties essential to language that can engage multiple modalities. We hypothesize that the neural tissue involved in language processing may not be prespecified exclusively by sensory modality (such as sound) but may entail polymodal neural tissue that has evolved unique sensitivity to aspects of the patterning of natural language. Such neural specialization for aspects of language patterning appears to be neurally unmodifiable in so far as languages with radically different sensory modalities such as speech and sign are processed at similar brain sites, while, at the same time, the neural pathways for expressing and perceiving natural language appear to be neurally highly modifiable.
Riviello, J. J., Kull, L., Troup, C., & Holmes, G. L. (2001). Cortical stimulation in children: Techniques and precautions. Techniques in Neurosurgery, 7(1), 12-18.
Cortical stimulation (CS) is important in planning epilepsy surgery in both adults and children. The goal of epilepsy surgery is seizure control without a significant neurologic deficit. The term eloquent cortex refers to cortical areas subserving the critical neurologic functions of motor, somatosensory, language, and memory. The identification of these areas is called cortical or functional mapping. CS may either activate or inhibit neurologic function from the stimulated area, thus identifying its function. CS also produces epileptiform activity, either spikes or sharp waves, called afterdischarges (ADs). The stimulation intensity that results in an AD is called the AD threshold. The techniques and precautions of CS are reviewed, including background electronic principles, stimulation parameters, and recording and testing methods, emphasizing its application to children. The immature cortex is more resistant to CS, which depends on the degree of myelination. Because more energy is needed to elicit a functional response in children, different stimulation parameters are used, especially a longer pulse duration. In addition, functional mapping in adults is generally performed at stimulation intensities below the AD threshold, whereas in younger children, functional responses may occur only above the AD threshold.
Roder, B., Rosler, F., & Neville, H. J. (2001). Auditory memory in congenitally blind adults: a behavioral- electrophysiological investigation. Cognitive Brain Research, 11(2), 289-303.
Blind people must rely more than sighted people on auditory input in order to acquire information about the world. The present study was designed to test the hypothesis that blind people have better memory than sighted individuals for auditory verbal material and specifically to determine whether memory encoding and/or retrieval are improved in blind adults. An incidental memory paradigm was employed in which 11 congenitally blind people and 11 matched sighted controls first listened to 80 sentences which ended either with a semantically appropriate or inappropriate word. Immediately following, the recognition phase occurred, in which all sentence terminal words were presented again randomly intermixed with the same number of new words. Participants indicated whether or not they had heard the word in the initial study phase. Event-related brain potentials (ERPs) were recorded from 28 electrode positions during both the encoding and the retrieval phase. Blind participants' memory performance was superior to that of sighted controls. In addition, during the recognition phase, previously presented words elicited ERPs with larger positive amplitudes than new words, particularly over the right hemisphere. During the study phase, words that would subsequently be recognized elicited a more pronounced late positive potential than words that were not subsequently recognized. These effects were reliable in the congenitally blind participants but could only be obtained in the subgroup of sighted participants who had the highest memory performance. These results imply that blind people encode auditory verbal material more efficiently than matched sighted controls and that this in turn allows them to recognize these items with a higher probability. (C) 2001 Elsevier Science B.V. All rights reserved.
Rosen, G., Willoch, F., Bartenstein, P., Berner, N., & Rosjo, S. (2001). Neurophysiological processes underlying the phantom limb pain experience and the use of hypnosis in its clinical management: An intensive examination of two patients. International Journal of Clinical and Experimental Hypnosis, 49(1), 38-55.
In a pilot study with 2 patients suffering from phantom limb pain (PLP), hypnotic suggestions were used to modify and control the experience of the phantom limb, and positron emission tomography (PET) was used to index underlying pathways and areas involved in the processing of phantom limb experience (PLE) and PLP. The patients' subjective experiences of pain were recorded in a semistructured protocol. PET results demonstrated activation in areas known to be responsible for sensory and motor processing. The reported subjective experiences of PLP and movement corresponded with predicted brain activity patterns. This work helps to clarify the central nervous system correlates of phantom limb sensations, including pain. It further suggests that hypnosis can be incorporated into treatment protocols for PLP.
Sampaio, E., Maris, S., & Bachy-y-Rita, P. (2001). Brain plasticity: 'visual' acuity of blind persons via the tongue. Brain Research, 908(2), 204-207.
The 'visual' acuity of blind persons perceiving information through a newly developed human-machine interface, with an array of electrical stimulators on the tongue, has been quantified using a standard Ophthalmological test (Snellen Tumbling E). Acuity without training averaged 20/860. This doubled with 9 h of training. The interface may lead to practical devices for persons with sensory loss such as blindness, and offers a means of exploring late brain plasticity. (C) 2001 Elsevier Science BY. All rights reserved.
Schoups, A., Vogels, R., Qian, N., & Orban, G. (2001). Practising orientation identification improves orientation coding in V1 neurons. Nature, 412(6846), 549-553.
The adult brain shows remarkable plasticity, as demonstrated by the improvement in fine sensorial discriminations after intensive practice. The behavioural aspects of such perceptual learning are well documented, especially in the visual system(1-8). Specificity for stimulus attributes clearly implicates an early cortical site, where receptive fields retain fine selectivity for these attributes; however, the neuronal correlates of a simple visual discrimination task remained unidentified. Here we report electrophysiological correlates in the primary visual cortex (V1) of monkeys for learning orientation identification. We link the behavioural improvement in this type of learning to an improved neuronal performance of trained compared to naive neurons. Improved long-term neuronal performance resulted from changes in the characteristics of orientation tuning of individual neurons. More particularly, the slope of the orientation tuning curve that was measured at the trained orientation increased only for the subgroup of trained neurons most likely to code the orientation identified by the monkey. No modifications of the tuning curve were observed for orientations for which the monkey had not been trained. Thus training induces a specific and efficient increase in neuronal sensitivity in V1. Shallice, T. (2001). 'Theory of mind' and the prefrontal cortex. Brain, 124, 247-248.
Shimojo, S., & Shams, L. (2001). Sensory modalities are not separate modalities: plasticity and interactions. Current Opinion in Neurobiology, 11(4), 505-509.
Historically, perception has been viewed as a modular function, with the different sensory modalities operating independently of each other. Recent behavioral and brain imaging studies challenge this view, by suggesting that cross-modal interactions are the rule and not the exception in perception, and that the cortical pathways previously thought to be sensory-specific are modulated by signals from other modalities.
Small, D. M., Zatorre, R. J., Dagher, A., Evans, A. C., & Jones-Gotman, M. (2001). Changes in brain activity related to eating chocolate: From pleasure to aversion. Brain, 124(Pt 9), 1720-33.
We performed successive H(2)(15)O-PET scans on volunteers as they ate chocolate to beyond satiety. Thus, the sensory stimulus and act (eating) were held constant while the reward value of the chocolate and motivation of the subject to eat were manipulated by feeding. Non- specific effects of satiety (such as feelings of fullness and autonomic changes) were also present and probably contributed to the modulation of brain activity. After eating each piece of chocolate, subjects gave ratings of how pleasant/unpleasant the chocolate was and of how much they did or did not want another piece of chocolate. Regional cerebral blood flow was then regressed against subjects' ratings. Different groups of structures were recruited selectively depending on whether subjects were eating chocolate when they were highly motivated to eat and rated the chocolate as very pleasant [subcallosal region, caudomedial orbitofrontal cortex (OFC), insula/operculum, striatum and midbrain] or whether they ate chocolate despite being satiated (parahippocampal gyrus, caudolateral OFC and prefrontal regions). As predicted, modulation was observed in cortical chemosensory areas, including the insula and caudomedial and caudolateral OFC, suggesting that the reward value of food is represented here. Of particular interest, the medial and lateral caudal OFC showed opposite patterns of activity. This pattern of activity indicates that there may be a functional segregation of the neural representation of reward and punishment within this region. The only brain region that was active during both positive and negative compared with neutral conditions was the posterior cingulate cortex. Therefore, these results support the hypothesis that there are two separate motivational systems: one orchestrating approach and another avoidance behaviours.
Stewart, L., Ellison, A., Walsh, V., & Cowey, A. (2001). The role of transcranial magnetic stimulation (TMS) in studies of vision, attention and cognition. Acta Psychologica, 107(1-3), 275-291.
Transcranial magnetic stimulation (TMS) can be conceptualized as a virtual lesion technique, capable of disrupting organized cortical activity, transiently and reversibly. The technique combines goad spatial and temporal resolution and, moreover, because it represents an interference technique, can be said to have excellent functional resolution. The following is a review and discussion of the contribution which TMS has made to the study of vision, attention, development and plasticity and speech, and language. (C) 2001 Elsevier Science B.V. All rights reserved.
Tyler, K. L., & Malessa, R. (2000). The Goltz-Ferrier debates and the triumph of cerebral localizationalist theory. Neurology, 55(7), 1015-1024.
Objective: To analyze the significance of the Goltz-Ferrier debates held at the International Medical Congress of 1881 for the development of ideas on cerebral localization. Background: Cerebral localization was the subject of vigorous debate throughout the 19th century. At the Congress of 1881, David Ferrier, a leading proponent of cerebral localization, and Friedrich Leopold Goltz, an equally prominent anti- localizationist, had the opportunity to present their experimental research before 3,000 of the world's leading medical figures. Methods: The authors reviewed and translated the presentations by Goltz and Ferrier at the Congress and supporting publications in contemporary medical journals. Results: In his presentation to the Physiology Section, Goltz criticized localizationists for their widely divergent conclusions about the exact anatomic sites of cortical centers and for their failure to adequately explain functional restitution after cortical ablations. He noted that localizationist theories could, like an apple, "look very tempting and still have a worm inside." He described his own studies on massive decerebrations in dogs and noted that despite complete destruction of the cortices of both hemispheres these animals failed to exhibit motor weakness or deficits in primary sensation. Ferrier noted that Goltz's results were irreconcilable with his own experiments in monkeys, in which circumscribed lesions produced clear and reproducible functional deficits. Both investigators exhibited animals with cortical ablations. Ferrier's presentation of a hemiplegic monkey prompted Charcot's famous utterance, "C'est un malade!" ["It's a patient!"]. A distinguished committee examined the brains of the animals, and confirmed that Ferrier had indeed succeeded in producing a circumscribed lesion in the frontoparietal cortex, whereas the cortical ablations in Goltz's dogs were much less widespread than anticipated. Conclusions: Ferrier's dramatic demonstration of the effects produced by localized lesions in macaques triumphed over Goltz's unitary view of brain function, providing a major impetus for the subsequent successful development of neurologic surgery.
Vuilleumier, P., Chicherio, C., Assal, F., Schwartz, S., Slosman, D., & Landis, T. (2001). Functional neuroanatomical correlates of hysterical sensorimotor loss. Brain, 124, 1077- 1090.
Hysterical conversion disorders refer to functional neurological deficits such as paralysis, anaesthesia or blindness not caused by organic damage but associated with emotional 'psychogenic' disturbances. Symptoms are not intentionally feigned by the patients whose handicap often outweighs possible short-term gains. Neural concomitants of their altered experience of sensation and volition are still not known. We assessed brain functional activation in seven patients with unilateral hysterical sensorimotor loss during passive vibratory stimulation of both hands, when their deficit was present and 2-4 months later when they had recovered. Single photon emission computerized tomography using Tc-99m-ECD revealed a consistent decrease of regional cerebral blood flow in the thalamus and basal ganglia contralateral to the deficit. Independent parametric mapping and principal component statistical analyses converged to show that such subcortical asymmetries were present in each subject. Importantly, contralateral basal ganglia and thalamic hypoactivation resolved after recovery. Furthermore, lower activation in contralateral caudate during hysterical conversion symptoms predicted poor recovery at followup. These results suggest that hysterical conversion deficits may entail a functional disorder in striatothalamocortical circuits controlling sensorimotor function and voluntary motor behaviour. Basal ganglia, especially the caudate nucleus, might be particularly well situated to modulate motor processes based on emotional and situational cues from the limbic system. Remarkably, the same subcortical premotor circuits are also involved in unilateral motor neglect after organic neurological damage, where voluntary limb use may fail despite a lack of true paralysis and intact primary sensorimotor pathways. These findings provide novel constraints for a modern psychobiological theory of hysteria.
Start | basic neuroanat. | reading | zeki extracts | table of links | List of Refs | Journals