Psychophysiology: Today and Tomorrow focuses on the most important theoretical aspects and practical outlets of the problem, as well as the main potentialities and interests of psychophysiology. Organized into 23 chapters, this book begins with the identification of component systems for syntax, verbal memory, focusing attention, and a system common to sequencing motor movements and phonemic discrimination. Subsequent chapter elucidates neurophysiological correlates of mental processes in man. Other chapters explore relations between electrical brain rhythms and behavior; brain exploration in psychophysiology; potentialities of neurophysiology in study and cure of mental disorders in epilepsy; and structural analysis of non-verbal thinking in man. The neuropharmacological analysis of the brain's functional organization in processes of formation and retrieval of memory engrams; role of neuropeptides in synapsomodification; and levels of functioning of transmitter systems and epileptogenesis are also explained.
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BRAIN ORGANIZATION FOR LANGUAGE: Identification of Component Systems for Syntax, Verbal Memory, Focusing Attention and a System Common to Sequencing Motor Movements and Phonemic Discrimination
G.A. Ojemann, Department of Neurological Surgery (RI 20), University of Washington, Seattle, WA 98195, USA
Publisher Summary
This chapter discusses brain organization for language. It also discusses a series of studies utilizing the electrical stimulation mapping technique during neurosurgical operations under local anesthesia where a variety of different language behaviors have been measured, including object naming, reading, short-term verbal memory, the control of single and sequential oral movements, and phonemic discrimination. In the medial central portions of ventral lateral thalamus, object naming can be disturbed by stimulation. It is suggested that this represents difficulty in the retrieval of names from long-term memory, a part of the same gating process of the specific alerting response. The naming task does not provide a sufficient variety of behavioral responses to classify the sites further, though one wonders if they might play a role in either retrieval from long-term memory or in some semantic aspect of language. The studies of naming in multilingual patients have indicated that there is a partial differential localization of cortex involved in naming in two languages. It remains to be determined whether these represent segregation of systems; for example, one might expect the syntactic system for the two languages to be differential, while the sequential movement–auditory discrimination system might be common to both languages.
An understanding of the physiological mechanisms used by the human brain for language must begin with anatomy, with the identification of what pieces of the brain play what role in language. From observations of language behaviour changes after strokes, the sites where stimulation changes naming, and more recently, the areas of brain that show evidence of increased work during language tasks, a traditional model has been developed of the brain areas for language. That model involves cortical structures in the dominant hemisphere, with an anterior zone just in front of the motor strip involved in motor, expressive aspects of language and a posterior zone in the region of the parietal-temporal junction involved in the receptive, understanding aspects of language. But there have always been problems with this traditional model. Most aphasic patients show both expressive and receptive deficits on careful testing (De Renzi and Vignolo, 1962). Sites of brain damage giving rise to a particular language disturbance often do not correspond to those predicted by the traditional model, particularly a lack of correlation between damage to the anterior language zone and the development of a motor aphasia (Mohr, 1976). And the traditional model cannot account for a number of language behaviours that are strongly lateralized to the dominant hemisphere, for example, short-term verbal memory (Albert, 1976) and the control of sequential motor movements (Mateer and Kimura, 1977). Nor does the traditional model of cortical language include the well confirmed evidence that subcortical, particularly thalamic lesions give rise to specific language disturbances (Fisher, 1958; Luria, 1977; Reynolds et al., 1978).
The present paper reviews a series of studies utilizing the electrical stimulation mapping technique during neurosurgical operations under local anaesthesia, where a variety of different language behaviours have been measured, including object naming, reading, short-term verbal memory, the control of single and sequential oral movements and phonemic discrimination. From these studies emerges a different model of what various regions of the dominant hemisphere do in relation to language. A limited region of premotor cortex in the dominant hemisphere is identified as a final common motor pathway for speech. The remainder of dominant hemisphere peri-Sylvian cortex is a brain region common to a sequential motor and auditory discrimination system. This includes not only frontal but also superior temporal and parietal regions. Cortex surrounding this both frontally and parieto-temporally is part of a system for short-term verbal memory. Interlaced between these two systems are specific cortical sites identified with control of syntax. Ventro-lateral thalamus in the dominant hemisphere contains a mechanism involved in controlling and maintaining attention on verbal material, a mechanism that is active in both language and short-term verbal memory. Although there is considerable individual variability in the exact cortical regions involved in each system, the relative relations between these systems in dominant hemispheres is quite constant.
MATERIALS AND METHODS
These studied were carried out during neurosurgical operations under local anaesthesia. Two patient populations are used. One group consists of patients undergoing stereotaxic thalamotomy for treatment of dyskinesias. These patients provide evidence on the role of lateral thalamus in language mechanisms. The other group includes patients with medically intractable epilepsy undergoing craniotomy for resection of an epileptic focus. These patients provided information on the role of language dominant cortex. The general technique has been the same in each patient population. A standardized test that provides repetitive samples of a particular language behaviour is administered to the patient in the operating room. During some trials of the test electrical stimulation is applied to specific sites in language cortex or thalamus and any changes in performance that occur during stimulation are compared to performance on interspersed trials without stimulation. Multiple sample of the effects of stimulation are obtained at each site in each patient. In patients undergoing thalamotomy, a single thalamic site is generally sampled, usually at multiple current levels, though all currents are less than those producing any evoked sensory or motor phenomena. For cortex, multiple sites in periSylvian cortex of dominant hemisphere have been sampled using the largest current level that does not produce locally recorded after-discharges in the sampled cortex. In all cases, stimulation is with 60 Hz,
msec total duration biphasic square wave pulses from a constant current stimulator, using stimulation trains that last through the particular sample of language behaviour, usually 4 seconds. Electrode location at subcortical sites is recorded on X-rays that also show the anterior and posterior commissures as standard radiologic landmarks. Cortical localization is obtained from photographs of the cortical surface by the relation to the cortical veins; stimulation sites are then reconstructed on venograms.
Four different language behaviour tests have been used in this study. The first test measures object naming and short-term verbal memory. It is published in Ojemann, Blick and Ward (1971). This is a visually presented test consisting of a series of slides, four to each trial, the entire test consisting of 60 consecutive trials. Within each trial the first slide is a measure of object naming: a picture of an object whose name is a common word with the words ‘This is a’ printed above it; the patient is trained to say ‘This is a’ and give the name of the object aloud. This is then followed by a distractor slide, a two-digit number greater than 30, which the patient is trained to read aloud and then count backwards from it by three’s aloud. Following this are two output slides for a single item test of post-distractional short-term verbal memory patterned after Peterson and Peterson (1959) with naming as input to memory and counting as a distractor during which the name must be stored in short-term memory. The first is output from memory by a cued recall, a slide with the word ‘recall’ on it appearing and the patient giving back the name of the object pictured on that trial. The second is output from memory by word recognition, a slide with four words appearing; one word is the name of the object on this trial, one the name of the object on the immediately preceding trial, and two other names of objects pictured elsewhere in the test. The patient reads the name of the object aloud. Stimulation occurs during the naming slide on some trials, the distractor slide on other trials, the cued recall slide on still other trials, the naming and cued recall slides together on still other trials and interspersed are trials with no stimulation which provide a measure of control performance. Multiple blocks of trials containing each of these test conditions are obtained at each site of stimulation. This test was used for the entire series of thalamic s...
Table of contents
Cover image
Title page
Table of Contents
Copyright
PREFACE
PART I: DIRECT CONTACT WITH THE HUMAN BRAIN
PART II: INDIRECT CONTACT WITH THE HUMAN BRAIN AND ANIMAL EXPERIMENTS
