Co-Planar Stereotaxic Atlas of the Human Brain—3-Dimensional Proportional System: An Approach to Cerebral Imaging, J. Talairach, P. Tournoux. Georg Thieme Verlag, New York (1988), 122 pp., 130 figs. DM 268

Information about the basal ganglia has accumulated at a prodigious pace over the past decade, necessitating major revisions in our concepts of the structural and functional organization of these nuclei. From earlier data it had appeared that the basal ganglia served primarily to integrate diverse inputs from the entire cerebral cortex and to "funnel" these influences, via the ventrolateral thalamus, to the motor cortex (Allen & Tsukahara 1974, Evarts & Thach 1969, Kemp & Powell 1971). In particular, the basal

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Parallel Organization of Functionally Segregated Circuits Linking Basal Ganglia and Cortex

Information processing in the cerebral cortex involves interactions among distributed areas. Anatomical connectivity suggests that certain areas form local hierarchical relations such as within the visual system. Other connectivity patterns, particularly among association areas, suggest the presence of large-scale circuits without clear hierarchical relations. In this study the organization of networks in the human cerebrum was explored using resting-state functional connectivity MRI. Data from 1,000 subjects were registered using surface-based alignment. A clustering approach was employed to identify and replicate networks of functionally coupled regions across the cerebral cortex. The results revealed local networks confined to sensory and motor cortices as well as distributed networks of association regions. Within the sensory and motor cortices, functional connectivity followed topographic representations across adjacent areas. In association cortex, the connectivity patterns often showed abrupt transitions between network boundaries. Focused analyses were performed to better understand properties of network connectivity. A canonical sensory-motor pathway involving primary visual area, putative middle temporal area complex (MT+), lateral intraparietal area, and frontal eye field was analyzed to explore how interactions might arise within and between networks. Results showed that adjacent regions of the MT+ complex demonstrate differential connectivity consistent with a hierarchical pathway that spans networks. The functional connectivity of parietal and prefrontal association cortices was next explored. Distinct connectivity profiles of neighboring regions suggest they participate in distributed networks that, while showing evidence for interactions, are embedded within largely parallel, interdigitated circuits. We conclude by discussing the organization of these large-scale cerebral networks in relation to monkey anatomy and their potential evolutionary expansion in humans to support cognition.

The organization of the human cerebral cortex estimated by intrinsic functional connectivity

As humans, we perceive feelings from our bodies that relate our state of well-being, our energy and stress levels, our mood and disposition. How do we have these feelings? What neural processes do they represent? Recent functional anatomical work has detailed an afferent neural system in primates and in humans that represents all aspects of the physiological condition of the physical body. This system constitutes a representation of 'the material me', and might provide a foundation for subjective feelings, emotion and self-awareness.

How do you feel? Interoception: the sense of the physiological condition of the body.

Magnetoencephalography (MEG) is a noninvasive technique for investigating neuronal activity in the living human brain. The time resolution of the method is better than 1 ms and the spatial discrimination is, under favorable circumstances, 2-3 mm for sources in the cerebral cortex. In MEG studies, the weak 10 fT-1 pT magnetic fields produced by electric currents flowing in neurons are measured with multichannel SQUID (superconducting quantum interference device) gradiometers. The sites in the cerebral cortex that are activated by a stimulus can be found from the detected magnetic-field distribution, provided that appropriate assumptions about the source render the solution of the inverse problem unique. Many interesting properties of the working human brain can be studied, including spontaneous activity and signal processing following external stimuli. For clinical purposes, determination of the locations of epileptic foci is of interest. The authors begin with a general introduction and a short discussion of the neural basis of MEG. The mathematical theory of the method is then explained in detail, followed by a thorough description of MEG instrumentation, data analysis, and practical construction of multi-SQUID devices. Finally, several MEG experiments performed in the authors' laboratory are described, covering studies of evoked responses and of spontaneous activity in both healthy and diseased brains. Many MEG studies by other groups are discussed briefly as well.

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Magnetoencephalography—theory, instrumentation, and applications to noninvasive studies of the working human brain

The generators and functional correlates of gamma oscillations within the sensorimotor cortex remain unclear. With the goal of locating the oscillations' sources precisely and then studying the relationship between oscillatory reactivity and ongoing movement, we recorded stereoelectroencephalograms with intracerebral electrodes in eight epileptic subjects awaiting surgical treatment. The sensorimotor cortex was free of lesions and was exhaustively explored with the electrodes. Subjects were asked to perform various self-paced movements contralateral to the exploration zone, brief and sustained, distal movements and a pointing movement. We used the event-related desynchronization method to quantify the reactivity of the 40-60-Hz band before, during and after the performance of movement. A very focused, event-related synchronization of gamma rhythms was found in all subjects. It was predominantly observed in the primary sensorimotor area and its distribution was consistent with the functional map established using electrical stimulations. Two different temporal patterns were observed, the event-related synchronization of gamma rhythms was related either to movement onset or to movement offset but was never recorded before movement. This observation suggests that gamma oscillations are more probably related to movement execution than to motor planning. The different patterns argue in favour of multiple functional roles; it has been shown that gamma oscillations may support the efferent drive to the muscles and here we show that they are also likely to be related to somatosensory integration. We therefore suggest that gamma oscillations in the 40-60-Hz band may support afferent sensory feedback to the sensorimotor cortex during the performance of movement.

Intracerebral study of gamma rhythm reactivity in the sensorimotor cortex

The first electrophysiological study of the human lateral geniculate nucleus (LGN), optic radiation, striate, and extrastriate visual areas is presented in the context of presurgical evaluation of three epileptic patients (Patients 1, 2, and 3). Visual-evoked potentials to pattern reversal and face presentation were recorded with depth intracranial electrodes implanted stereotactically. For Patient 1, electrode anatomical registration, structural magnetic resonance imaging, and electrophysiological responses confirmed the location of two contacts in the geniculate body and one in the optic radiation. The first responses peaked approximately 40 milliseconds in the LGN in Patient 1 and 60 milliseconds in the V1/V2 complex in Patients 2 and 3. Moreover, steady state visual-evoked potentials evoked by the unperceived but commonly experienced video-screen flicker were recorded in the LGN, optic radiation, and V1/V2 visual areas. This study provides topographic and temporal propagation characteristics of steady state visual-evoked potentials along human visual pathways. We discuss the possible relationship between the oscillating signal recorded in subcortical and cortical areas and the electroencephalogram abnormalities observed in patients suffering from photosensitive epilepsy, particularly video-game epilepsy. The consequences of high temporal frequency visual stimuli delivered by ubiquitous video screens on epilepsy, headaches, and eyestrain must be considered.

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Human lateral geniculate nucleus and visual cortex respond to screen flicker

Objectives: To quantify the morphologic changes of temporopolar structures to better understand the pathophysiology of anterior temporal white matter increased T2 signal observed in temporal lobe epilepsy (TLE). Methods: MRI was performed in 30 patients with TLE and in 30 normal control subjects and independently assessed by visual analysis and quantitative measurements. Specifically, the temporal pole (TP) volume, as well as its gray and white matter components, was measured using three-dimensional T1 MR images and a semiautomatic protocol. The authors tested whether the presence of an increased T2-weighted signal in the anterior temporal white matter was associated with significant TP atrophy. The associations between the TP volume and MRI signs of hippocampal sclerosis, age at onset, seizure frequency, duration of illness, and a history of febrile convulsions were also studied. Results: Both right and left TLE populations demonstrated a reduction of the temporopolar white and gray matter volumes ipsilateral to seizure onset ( p p p Conclusions: The temporal pole is frequently atrophic ipsilateral to seizure onset in refractory TLE. The association between TP atrophy and ISWM suggests that both abnormalities might derive from a common pathologic process.

Temporopolar changes in temporal lobe epilepsy A quantitative MRI-based study

Thalamic pain is a severe and treatment-resistant type of central pain that may develop after thalamic stroke. Lesions within the ventrocaudal regions of the thalamus carry the highest risk to develop pain, but its emergence in individual patients remains impossible to predict. Because damage to the spino-thalamo-cortical system is a crucial factor in the development of central pain, in this study we combined detailed anatomical atlas-based mapping of thalamic lesions and assessment of spinothalamic integrity using quantitative sensory analysis and laser-evoked potentials in 42 thalamic stroke patients, of whom 31 had developed thalamic pain. More than 97% of lesions involved an area between 2 and 7 mm above the anterior-posterior commissural plane. Although most thalamic lesions affected several nuclei, patients with central pain showed maximal lesion convergence on the anterior pulvinar nucleus (a major spinothalamic target) while the convergence area lay within the ventral posterior lateral nucleus in pain-free patients. Both involvement of the anterior pulvinar nucleus and spinothalamic dysfunction (nociceptive thresholds, laser-evoked potentials) were significantly associated with the development of thalamic pain, whereas involvement of ventral posterior lateral nucleus and lemniscal dysfunction (position sense, graphaesthesia, pallaesthesia, stereognosis, standard somatosensory potentials) were similarly distributed in patients with or without pain. A logistic regression model combining spinothalamic dysfunction and anterior pulvinar nucleus involvement as regressors had 93% sensitivity and 87% positive predictive value for thalamic pain. Lesion of spinothalamic afferents to the posterior thalamus appears therefore determinant to the development of central pain after thalamic stroke. Sorting out of patients at different risks of developing thalamic pain may be achievable at the individual level by combining lesion localization and functional investigation of the spinothalamic system. As the methods proposed here do not need complex manipulations, they can be added to routine patients' work up, and the results replicated by other investigators in the field.

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François Mauguière

Papers

Intracerebral study of gamma rhythm reactivity in the sensorimotor cortex

Human lateral geniculate nucleus and visual cortex respond to screen flicker

Temporopolar changes in temporal lobe epilepsy A quantitative MRI-based study

Thalamic pain: anatomical and physiological indices of prediction

Somatosensory evoked potentials. The International Federation of Clinical Neurophysiology.