Brain organization for language from the perspective of electrical stimulation mapping

Neuronal activity in the human lateral temporal lobe. I. Responses to speech

Single and multiple unit neuronal activity was recorded from the cortex of the lateral temporal lobe in conscious humans during open brain surgery for the treatment of epilepsy. Recordings were obtained from the right and left superior, middle and inferior temporal gyrus of 34 patients (41 recording sites). Recordings were restricted to regions to be resected during subsequent surgery. This excluded recordings from language areas proper. Neuronal responses to words and sentences presented over a loudspeaker and during free conversation were recorded. No significant differences between the right and left hemisphere were obvious. All neurons in the superior temporal gyrus responded to various aspects of spoken language with temporally well defined activation/inhibition patterns, but not or only little to non-linguistic noises or tones. Excitatory responses were typically short or prolonged (up to several hundred ms) bursts of discharges at rates above 20/sec, reaching peak rates of 50-100/s. Such responses could be specifically related to certain combinations of consonants suggesting a function in categorization, they could depend on word length, could differentiate between polysyllabic and compound words of the same length or could be unspecifically related to language as such. No formant specific responses were found, but the prolonged excitations across syllables suggest that consonant/vowel combinations may play a role for some activation patterns. Responses of some neurons (or neuronal populations) depended on the attention paid to the words and sentences, or the task connected with them (repeat words, speech addressed to the patient demanding something). Neurons in the middle and inferior temporal gyrus were only little affected by listening to single words or sentences, but some were unspecifically activated by words or while listening to sentences. Excitatory responses varied within a limited range of discharge rates usually below 5-10/s. Phonetic distortion of spoken language could reduce responses in superior temporal gyrus neurons, but also the slight changes in discharge rate of middle temporal neurons could be absent during distorted and uncomprehensible speech sounds. We conclude that superior temporal gyrus neuron responses reflect some general phonetic but not semantic aspects of spoken language. Middle and inferior temporal gyrus neurons do not signal phonetic aspects of language, but may be involved in understanding language under certain conditions.

Motor-motor adaptation: preliminary findings

This study investigated the relationship between speech perception and speech production. An experimental technique called motor-motor adaptation was devised. Subjects produced a speech token repeatedly (20 to 40 repetitions), then produced a second token one time. These tokens all contained stop consonants and were subsequently analyzed for voice onset time. The results paralleled previous findings using the experimental procedure, perceptuomotor adaptation. The present study supports the notion of a perception-production link.

Tumour-surgery within the central motor strip: surgical results with the aid of electrical motor cortex stimulation

Surgery of tumours within or close to the central motor area always carries the risk of a new or increased postoperative motor deficit. One reason may be the difficulty of localizing the sensorimotor region, when it is displaced or distorted by the tumour and the perifocal oedema. Recently anatomical data of the craniocerebral topography of the central sulcus became available. We safely used under general anaesthesia the intraoperative mapping of the motor cortex by direct cortical electrical stimulation. In 21 patients tumours adjacent to or within the motor area were microsurgically resected. As a result of intraoperative localization the surgical approach had to be modified in contrast to the preoperative localization of the lesion in 5 patients. No new or increased motor deficit occurred and in some cases the preoperative weakness was reduced remarkably.

Cortical language localization in left, dominant hemisphere. An electrical stimulation mapping investigation in 117 patients

The localization of cortical sites essential for language was assessed by stimulation mapping in the left, dominant hemispheres of 117 patients. Sites were related to language when stimulation at a current below the threshold for afterdischarge evoked repeated statistically significant errors in object naming. The language center was highly localized in many patients to form several mosaics of 1 to 2 sq cm, usually one in the frontal and one or more in the temporoparietal lobe. The area of individual mosaics, and the total area related to language was usually much smaller than the traditional Broca-Wernicke areas. There was substantial individual variability in the exact location of language function, some of which correlated with the patient's sex and verbal intelligence. These features were present for patients as young as 4 years and as old as 80 years, and for those with lesions acquired in early life or adulthood. These findings indicate a need for revision of the classical model of language localization. The combination of discrete localization in individual patients but substantial individual variability between patients also has major clinical implications for cortical resections of the dominant hemisphere, for it means that language cannot be reliably localized on anatomic criteria alone. A maximal resection with minimal risk of postoperative aphasia requires individual localization of language with a technique like stimulation mapping.

Selective posterior cerebral artery injection of amytal: new method of preoperative memory testing

The carotid Amytal test (Wada test) was introduced, in 1948 by Wada, to localize speech function before temporal lobectomy in patients with medically refractory epilepsy, and it remains the standard for that purpose. The same test has also been used since 1962 to evaluate memory function; however, the adequacy of the test in this application has been viewed with increasing skepticism in recent years. Therefore, we developed an alternative to the Wada test. It consists of selective injection of Amytal into the posterior cerebral artery (PCA). This PCA Amytal test is designed to test only memory function (not language). We present several anatomic and functional reasons why this approach should be superior to the Wada test for this purpose. We also present preliminary data in support of this hypothesis. To date, we have had successful results of the PCA Amytal test in 38 of 45 patients (84%), and one major complication has occurred (2%).

Tonotypic cortical representation in man (case report)

Cortical stimulation--evoked perception of tones differing in pitch suggests that the perception of pitch may be discretely organized in the human auditory parakoniocortex. Findings, obtained from a neurosurgical patient undergoing temporal lobectomy, are discussed with reference to anatomical and functional considerations of the auditory parakoniocortex in humans. These tonotypic findings are potentially significant since, as previously reported, auditory sensations have not been analyzed in relation to perceptual categories of pitch.

Validation of Language Localisation by Computer Assisted Tomographic and Topographic Techniques

Computerized tomographic procedures have been used extensively since their introduction to examine specific language disabilities in aphasic patients and to correlate anatomical and clinical changes. The resulting overwhelming evidence in favour of lateralisation and localisation has been confirmed by regional blood flow studies and punctate electrical stimulation as well as by the topographic maps provided by neurometries. That specific lexical functions are localised within the peri-Sylvian cortex in the left cerebral hemisphere is now generally accepted, but the macroscopic mapping, which largely ignores the contribution of the ipsilateral thalamus and possibly of the basal nuclei, must not be mistaken for the language encoding processes in the parallel pathways which have been identified.

Cerebral organization of verbal and motor functions in left-handed and right-handed adults: effects of concurrent verbal tasks on unimanual tapping performance

Two experiments were conducted to study the interference effects of different concurrent verbal tasks on unimanual single-finger tapping and unimanual sequential finger tapping. Experiment 1 involved 24 right-handed university students. In the dual-task conditions, right-handers showed a greater right-hand than left-hand performance reduction for single-finger tapping, and an equal right-hand and left-hand reduction for sequential tapping. Experiment 2 involved 60 left-handed university students, divided into four groups according to familial sinistrality and writing hand posture. In the dual-task conditions, left-handers showed a greater left-hand than right-hand performance reduction for single-finger tapping, and an equal left-hand and right-hand reduction for sequential finger tapping. A dichotic listening task revealed a left hemispheric dominance for auditory linguistic functioning in most of the left-handers. Familial sinistrality and hand posture, on the whole, did not influence tapping performances. However, these factors influenced the ear asymmetries on the dichotic listening task. It is speculated that, with single-finger tapping, interference only takes place beyond the point of language motor programming, that is to say, at the motor areas and the supplementary motor areas of the cortex.

Epigenesis and the evolution of the human brain

This article proposes an hypothesis for the evolution of the human brain. It is based on the concepts of (i) regulation of nerve cell proliferation, and (ii) selective stabilisation of synapses during development. The former process is supposed to be rigidly regulated by the genome, while the latter (selective stabilisation) is proposed as developing in a more plastic manner. It is suggested here that genetic alterations of the regulation of neuroblast proliferation led to epigenetic rearrangements in selective synapse stabilisation, thus producing significant changes in cerebral connectivity. This view is in agreement with the punctuationalist theory of human evolution, and differs from other approaches to human nature, such as structuralist grammar and sociobiology.

Some general physiological principles of the human brain functioning

Implantation of electrodes into the human brain for diagnosis and therapy of different brain disorders enabled the revelation of some general and specific regularities in the brain functioning which, being properly accounted for, may promote further more efficient brain research with both invasive and non-invasive techniques. This is a discussion of three major principles revealed during comprehensive study of the human brain, including stimulation and recording of the broad range of physiological processes both in a relaxed state and when performing a set of psychological tests. (1) The presence of the flexible links in the cerebral systems subserving complex activity; (2) cerebral restrictive and protective mechanisms; (3) the ability of certain brain areas to respond selectively to the erroneous recognition of a given type of activity--error detection.

Surgical therapy for medically intractable epilepsy

There has been a recent renewal of interest in surgical therapy for medically intractable epilepsies. Cortical resection and callosotomy are the most widely accepted modes of surgical management. The indications for each of these approaches are reviewed. Although there has been much interest in imaging techniques, including positron emission tomography, to identify epileptogenic zones, identification still depends primarily on the electroencephalogram (EEG). There are several approaches to the evaluation and intraoperative management of patients undergoing cortical resection for temporal lobe epileptogenic zones. These range from selection based on scalp interictal EEG criteria, with resections guided by electrocorticography and functional mapping, to selection based on the location of ictal onset as recorded by chronically implanted depth electrodes, with an anatomically standard resection of the temporal lobe or resection limited to amygdalohippocampectomy. No one approach provides the optimum balance of benefits to risks and costs for all patients. The relative value of the different approaches for various populations of patients with medically intractable partial complex seizures is reviewed. Techniques for minimizing the morbidity of these operations, especially in regard to language and memory, are also discussed, as are the contributions to an understanding of the neurobiology of human epilepsy and human higher functions derived from the surgical therapy of epilepsy.

Compulsive thalamic self-stimulation: a case with metabolic, electrophysiologic and behavioral correlates

A 48-year-old woman with a stimulating electrode implanted in the right thalamic nucleus ventralis posterolateralis developed compulsive self-stimulation associated with erotic sensations and changes in autonomic and neurologic function. Stimulation effects were evaluated by neuropsychologic testing, endocrine studies, positron emission tomographic measurements of regional cerebral metabolic rate for glucose, EEG and evoked potentials. During stimulation, vital signs and pupillary diameter increased and a left hemiparesis and left hemisensory loss developed. Verbal functions deteriorated and visuospatial processing improved. Plasma growth hormone concentrations decreased, and adrenocorticotrophic hormone and cortisol levels rose. With stimulation, glucose metabolism increased in both thalami and both hemispheres, reversing baseline right-sided hypometabolism and right-left asymmetries. EEG and both somatosensory and brain-stem auditory evoked potentials remained unchanged during stimulation, while visual evoked potentials revealed evidence of anterior visual pathway dysfunction in the left eye. This case establishes the potential for addiction to deep brain stimulation and demonstrates that widespread behavioral and physiological changes, with concomitant alteration in the regional cerebral metabolic rate for glucose, may accompany unilateral thalamic stimulation.

Evidence that fixation digits can contribute to visual field asymmetries in lateralized tachistoscopic tasks

Fixation point digits have been widely used in tachistoscopic laterality studies as a simple and convenient means of ensuring unihemispheric projection of stimulus materials to the hemispheres. Previous findings demonstrate that fixation digits do not influence asymmetries in recognition accuracy studies with adult Ss. Present results, comparing four conditions differing in their use of fixation digits, show that in the naming latency paradigm the requirement to remember and report fixation control digits significantly augments RVF superiority. Implications for other latency tasks are discussed.

The "forced-attention paradigm" in dichotic listening to CV-syllables: a comparison between adults and children

The present study was concerned with the effects of directional attention on the right-ear-advantage (REA) in dichotic listening. It was suggested that if selective attention contributes to the REA during a non-forced, free recall condition, then comparing the unattended left and right ear scores when attention is forced to the right and the left ear, respectively, would yield an "attention-free" estimate of the REA. Each subject participated in a non-forced, free recall, condition; in a forced-right condition; and in a forced-left condition. During the two forced conditions, subjects were instructed to only attend to and report the right and left ear inputs, respectively. The stimuli were the six stop-consonants paired with the vowel a. Four right-handed groups participated (N = 18): Adult males, adult females, boys (8-9 years), girls (8-9 years). The results showed a significant REA in all groups during the non-forced condition. During the forced-right condition, significantly more correct recalls were obtained from the right compared to the left ear in all groups. During the forced-left condition, significantly more correct recalls from the left compared to the right ear was obtained only in the two adult groups, but not in the children groups. Finally, comparing correct recalls from the unattended right ear (during the forced-left condition) with the unattended left ear (during the forced-right condition) revealed a significant REA in all groups except for the adult females.

Visual event-related potentials to colored patterns and color names: attention to features and dimension

Four right-handed males and 4 right-handed females were instructed to match pairs of stimuli (colored flashes with either colored patterns or color names) presented sequentially to the central retina. Subjects were to respond to the second stimulus of a pair when it matched the first stimulus in terms of sensory color or word meaning. ERPs recorded from the second stimulus of a pair over occipital and frontal cortical regions indicate the following: Interdimension effects reflect an early and more global discrimination process between colored patterns and word patterns per se. The source of this effect appears to be localized in occipital cortical regions. Intradimension effects were evident later in time and reflect a more refined discrimination process between particular features within a dimension rather than between dimensions. The intradimension color effect began earlier in time than the word effect (229 msec versus 318 msec in the occipital data) and appears to be localized in posterior temporal regions. The onset of the word effect appears to have two neural generators: an early effect localized in frontal regions (274 msec) and a later effect localized in occipital regions (318 msec). The hierarchical model of language processing seems to hold true predominantly in posterior cortical regions. Effects associated with linguistic processing were evident in frontal regions before effects were noted in the occipital regions. This result suggests that either: word information is processed simultaneously and independently in the different regions, or anterior regions feedback onto posterior regions and, therefore, influence the processing in this region.

Sex differences in brain organization: implications for human communication

This article reviews current knowledge in two major research domains: sex differences in neuropsychophysiology, and in human communication. An attempt was made to integrate knowledge from several areas of brain research with human communication and to clarify how such a cooperative effort may be beneficial to both fields of study. By combining findings from the area of brain research, a communication paradigm was developed which contends that brain-related sex differences may reside largely in the area of communication of emotion.

Sexual dimorphism of auditory activity in the zebra finch song system

While the tracheosyringeal motor neurons of anesthetized male zebra finches fire in response to acoustic stimuli, the same motor neurons in females show no such response. Females masculinized by estradiol implants on Days 1 or 2 after hatching may develop auditory responses in their tracheosyringeal motor neurons; the presence of the response is directly related to the degree of masculinization of the estradiol-treated females' telencephalic song centers. In male zebra finches, neurons in HVc (Hyperstriatum Ventrale pars caudalis) respond to sound, and the HVc is necessary for the tracheosyringeal auditory response. Multiunit auditory activity was demonstrated in the HVc of female zebra finches. A single 20-microA pulse delivered to the male HVc elicits a large volley in the tracheosyringeal nerve; microstimulating the female HVc does not evoke a response in the motor nerve. This failure of both auditory and HVc stimulation to elicit a response in the female tracheosyringeal nerve is attributed to the lack of a functional HVc-nucleus Robustus Archistriatalis projection in females. If, as has been suggested, the tracheosyringeal auditory response may be important for the processing of song, female zebra finches might not process song in the same manner as do males.

Hypotheses on mnemonic information processing by the brain

From a neuropsychological point of view, hypotheses are offered on the possible action of the brain in the processing of mnemonic information for long-term storage (or for retrieval of long-term stored information). It is argued that strict relations between damage of circumscribed brain structures and amnesia, as they have been suggested in recent case reports, are questionable for several reasons: Firstly, the involved regions differ between cases; secondly, there is some counter-evidence from other cases in which similar neuronal damage failed to result in lasting amnesic disturbances; thirdly, it is hypothesized that even from circumscribed brain damage it is not justifiable to conclude that the lesioned structure is solely or principally responsible for the observed mnemonic changes, as the brain acts in an integrative way, that is, on the basis of a wide-spread network of neuronal information processing. On the basis of these and related arguments, hypotheses and models on mnemonic information processing in the intact and in the damaged brain are derived. With these hypotheses even the frequent observation of interindividual differences in mnemonic information processing finds a possible explanation which is in conformity to known anatomical circuits and connections and to principles of neuronal coding.

Auditory responses in avian vocal motor neurons: a motor theory for song perception in birds

The hypoglossal motor neurons that innervate the vocal organ (syrinx) of the male zebra finch show a selective, long-latency (50-millisecond) response to sound. This response is eliminated by lesions to forebrain song-control nuclei. Different song syllables elicit a response from different syringeal motor neurons. Conspecific vocalizations may therefore be perceived as members of a set of vocal gestures and thus distinct from other environmental sounds. This hypothesis is an avian parallel to the motor theory of speech perception in humans.

The neuropathology of amnesia

Relations between brain damage and memory disturbance are outlined with emphasis on the so-called amnesic syndrome. Following a brief introduction into forms of memory and memory failures, the basic causes of brain damaage (with relevance to amnestic failures) are described. Thereafter, the two best-known forms of brain damage-amnesia relations are reviewed: the consequences of damage to medial temporal lobe structures and to diencephalic regions. For the cases with medial temporal lobe damage, evidence is reported in greater detail for H.M., who has been examined more than any other amnesic patient for more than 30 years now, as a considerable amount of literature has accumulated on his behavior in diverse situations. Other cases with more or less circumscribed damage to medial temporal lobe structures are reviewed so as to outline criteria for or against the hypothesis that there are regions within the medial temporal lobe whose damage might be critical for the amnesic syndrome. Two cases of diencephalic amnesia are summarized in particular (cases of Mair et al., 1979) as they have received extensive neuropsychological and neuropathological investigation. Other cases with, for example, Korsakoff's disease are reviewed, as well as cases with diencephalic, or combined mesencephalic-diencephalic damage without nutritional causes. A third group of patients with massive, but still selective amnesic disturbances are then described: cases of basal forebrain damage, followed by descriptions of Alzheimer's disease which has similarities in the underlying neuropathology. This leads over to cases with more generalized intellectual deteriorations (dementia), which may have developed on the basis of primarily cortical damage or damage principally to basal ganglia structures. After reviewing cases with mainly material-specific memory failures--usually as a consequence of restricted neocortical damage--a separate section follows on patients in whom retrograde amnesia is the prominent symptom. The contribution of animal models of human amnesia is critically reviewed and discrepancies are analyzed between human and animal memory disturbances. This section emphasizes the value of investigating inter-dependencies between brain structures by pointing out that relations between memory disturbances and brain damage may be more complicated than apparent from a simple structure-function assignment. This aspect is further followed up in the conclusions.

Verbal memory deficits after left temporal lobectomy for epilepsy. Mechanism and intraoperative prediction

Verbal memory deficits remain a major complication of dominant hemisphere temporal lobectomy for epilepsy. The extent of this deficit was assessed preoperatively and 1 month and 1 year postoperatively with the Wechsler Verbal Memory Scale (WMSV) in 14 adults undergoing left temporal lobectomy. Intraoperative localization of language and verbal memory was also performed by electrical stimulation mapping. The WMSV score decreased an average of 22% at 1 month (13 cases), and 11% at 1 year (10 cases), even though in the majority of cases the medial extent of the resections had been significantly modified as a result of preoperative memory changes in response to intracarotid amobarbital perfusion testing. Memory decline was greater in patients who were not seizure-free, and correlated with the lateral (but not the medial) extent of the resection. The memory deficit could be predicted intraoperatively with 80% accuracy from the relationship of the resection to sites identified by electrical stimulation mapping as essential to naming or input or storage aspects of memory. This technique was applied prospectively in two additional cases with left temporal epileptic foci and complete verbal memory loss with left hemisphere amobarbital inactivation. These resections were tailored to avoid the essential naming and memory sites; the WMSV score increased 1 month postoperatively in both cases. This study identifies a lateral cortical component for verbal memory. Sites essential for that component can be localized intraoperatively with stimulation mapping; when they are spared in a resection, verbal memory deficit following dominant hemisphere temporal lobectomy can be prevented even in high-risk cases.