Beta EEG band: A measure of functional brain damage and language reorganization in aphasic patients after recovery

Functional reorganization of language was investigated in a group of eleven non-fluent aphasic patients after linguistic recovery and in a group of matched healthy adults. The ElectroEncephaloGram (EEG) was recorded from 38 scalp electrodes and high-beta band (21–28 Hz), an index of cognitive cortical arousal, was computed as normalized percentage across 0–100 Hz spectral range in six electrode clusters during three linguistic tasks: Phonological, Semantic and Orthographic/visuo-perceptual. During the Phonological task, controls showed greater beta activation on left versus right central cluster, whereas aphasic patients exhibited an inverted pattern of lateralization. In addition, patients' left central cluster, located over the core lesion, showed reduced beta activity with respect to controls. A similar inhibited activation was found in aphasics' left posterior cluster located over undamaged areas. At left anterior locations, aphasics, unlike controls, exhibited larger left versus right beta activity during both Phonological and Orthographic/visuo-perceptual tasks. Results point to substantial reorganization of language in recovered non-fluent aphasics at left prefrontal sites located anterior to the damaged Broca's area and inhibited language-related activation in left posterior undamaged, but disconnected, regions.     

Delta EEG Band as a Marker of Left Hypofrontality for Language in Schizophrenia Patients

Frontal hypoactivation has consistently been demonstrated in schizophrenia patients. We hypothesized that this well-known deficit is asymmetrical, ie, centered over left frontal locations and, in-line with Crow''s theory, associated with both loss of linguistic asymmetry and correlated with positive symptoms. Electroencephalography delta band was used as a quantitative index of cortical inhibition in 17 paranoid schizophrenia patients with prevailing positive symptoms and 17 matched control subjects. Delta amplitude was measured by 38 electrodes, while participants performed 3 linguistic tasks, visuoperceptual, rhyming, and semantic judgment. Compared with control subjects, patients did not show overall delta band differences, revealing no detrimental effects of pharmacological treatment. In healthy participants, analysis of 4 quadrants/regions of interest revealed higher delta amplitude in right vs left anterior sites, indicating significant left anterior disinhibition during linguistic processing. Instead, patients showed bilateral delta band distribution and, compared with control subjects, significant greater delta amplitude (ie, brain inhibition) in linguistic left anterior centers. Patients’ left hypofrontality was functionally related to their lack of hemispheric specialization for language and was positively correlated with higher levels of delusions (P1) and conceptual disorganization (P2) Positive and Negative Syndrome Scale subscales. Results suggest, in schizophrenia patients, a functional deficit of Broca''s area, a region playing a fundamental hierarchical role between and within hemispheres by integrating many basic processes in linguistic and conceptual organization. The significant correlation between lack of anterior asymmetry and increased positive symptoms is in-line with Crow''s hypothesis postulating the etiological role of disrupted linguistic frontal asymmetry on the onset of the key symptoms of schizophrenia.     

Inverted EEG theta lateralization in dyslexic children during phonological processing

The phonological deficit hypothesis of dyslexia has been investigated in the present research by analysing language-related lateralization of the EEG theta band in a sample of dyslexic children. To this aim, a paradigm based on word-pair visual presentation was used in which the same words were processed in Semantic and Phonological tasks. Theta band amplitude, a cortical index that has been related to working memory processing, was analysed during four different phases of word elaboration, thus allowing to measure also the temporal dynamics of word reading/encoding in the verbal working memory. Control subjects showed a specific (and therefore efficient) task-related and time-dependent cortical activation: a peak of theta activity during word reading was found that decayed during the next inter stimulus interval. Furthermore, during word presentation in the Phonological task, theta amplitude was greater on the left hemisphere. Dyslexics evidenced an altered pattern of theta activation both in the temporal dimension and in the cortical space: their peak of activity was delayed to the first inter stimulus interval after word offset and was shifted to the right hemisphere throughout the whole epoch of Phonological task and in two phases of the Semantic task. Analysis of alpha band failed to replicate the complex pattern of lateralization found for theta band in the two groups, a result that suggests a specific functional role of theta band, which cannot be interpreted as a simple marker of cortical inhibition. Results point to a deficit, in dyslexic children, to recruit left hemisphere structures for the elaboration of the phonological component of the verbal working memory. This deficit was marked by a different, unspecific and dysfunctional hemispherical asymmetry of theta activation to language, a deficit that involved also the time course of phonological linguistic elaboration.     

Hemispheric alpha asymmetries for auditorily presented words of high and low visual imagery during tasks of recognition and recall of aphasic and normal subjects

Abstract

Hemispheric alpha asymmetries of normal males, normal females, and male aphasics were observed from anterior and posterior placement sites for recall and recognition of high and low imagery words and during resting conditions. Results revealed no hemispheric asymmetries across tasks and electrode placement sites for the two normal groups. Females were found to have consistently higher mean alpha amplitude values than the normal males across conditions and tasks. Aphasic subjects, both fluent and nonfluent, demonstrated greater right hemisphere alpha suppression across tasks and conditions. No significant alpha asymmetries were found between groups during the resting condition. All subjects recognized more words than they recalled. High imagery words were more readily recognized or recalled than low imagery words. Results of the investigation are discussed relative to greater use of right hemisphere processing resources by aphasic subjects for processing linguistic information.     

Anomia in patients with left inferior temporal lobe lesions

Background: Damage to left inferior temporal cortex has been associated with naming deficits resulting either from impaired access to phonological word forms (pure anomia) or from degraded semantic knowledge (semantic anomia). Neuropsychological evidence indicates that pure anomia may follow damage to posterior inferior temporal cortex (BA 37), whereas semantic anomia is associated with damage to more anterior temporal lobe regions (BA 20, 21, 38). By contrast, some investigators have suggested that it is the overall severity of anomia, rather than the nature of the underlying cognitive impairment, that is affected by the anterior extent of the lesion. Aims: To examine the naming performance of patients with left inferior temporal lobe damage and determine whether anterior extension of the lesion influences the nature and/or the severity of the naming impairment. Methods & Procedures: Eight participants with focal damage to left inferior temporal cortex completed a battery of language measures that included confrontation naming, semantic processing, and single‐word reading and spelling. Degree and type of anomia was examined relative to anterior lesion extension using both visual inspection and statistical analyses. Outcomes & Results: Naming performance ranged from unimpaired to severely defective, with only two participants demonstrating an additional mild impairment of semantic knowledge. The underlying mechanism of anomia seemed to be degraded access to phonological word forms in all participants, regardless of lesion configuration. The severity of the naming impairment was positively correlated with anterior extension of the lesion towards the temporal pole, although additional analyses suggested that these findings were significantly influenced by participant age. Naming was not correlated with performance on the nonverbal semantic task or any other demographic variable. Conclusions: The behavioural and neuroanatomical findings provide modest support for the hypothesis that a relationship exists between anterior lesion extension and the severity of concomitant anomia in patients with left inferior temporal lobe damage. The data suggest that such lesions may disconnect relatively preserved semantic knowledge from regions critical for access to phonological word forms. However, additional research is needed to discern to what extent age and individual variability temper these effects.     

Lexical retrieval and semantic knowledge in patients with left inferior temporal lobe lesions

Background: It has been proposed that anomia following left inferior temporal lobe lesions may have two different underlying mechanisms with distinct neural substrates. Specifically, naming impairment following damage to more posterior regions (BA 37) has been considered to result from a disconnection between preserved semantic knowledge and phonological word forms (pure anomia), whereas anomia following damage to anterior temporal regions (BAs 38, 20/21) has been attributed to the degradation of semantic representations (semantic anomia). However, the integrity of semantic knowledge in patients with pure anomia has not been demonstrated convincingly, nor were lesions in these cases necessarily confined to BA 37. Furthermore, evidence of semantic anomia often comes from individuals with bilateral temporal lobe damage, so it is unclear whether unilateral temporal lobe lesions are sufficient to produce significant semantic impairment.

Aims: The main goals of this study were to determine whether anomia following unilateral left inferior temporal lobe damage reflected a loss of semantic knowledge or a post‐semantic deficit in lexical retrieval and to identify the neuroanatomical correlates of the naming impairment.

Methods & Procedures: Eight individuals who underwent left anterior temporal lobectomy (L ATL) and eight individuals who sustained left posterior cerebral artery strokes (L PCA) completed a battery of language measures that assessed lexical retrieval and semantic processing, and 16 age‐ and education‐matched controls also completed this battery. High‐resolution structural brain scans were collected to conduct lesion analyses.

Outcomes & Results: Performance of L ATL and L PCA patients was strikingly similar, with both groups demonstrating naming performance ranging from moderately impaired to unimpaired. Anomia in both groups occurred in the context of mild deficits to semantic knowledge, which manifested primarily as greater difficulty in naming living things than nonliving things and greater difficulty in processing visual/perceptual as opposed to functional/associative semantic attributes. Lesion analyses indicated that both patient groups sustained damage to anterior inferior temporal lobe regions implicated in semantic processing.

Conclusions: These results contribute to a better understanding of the cognitive mechanism of naming impairment in patients with temporal lobe damage and support the notion that pure anomia and semantic anomia represent two endpoints along a continuum of semantic impairment. Unilateral left temporal lobe lesions in our patients resulted in relatively mild semantic deficits that were apparent primarily in lexical production tasks, whereas severe semantic impairment likely requires bilateral temporal lobe damage.     

Language lateralization in phonological, semantic and orthographic tasks: a slow evoked potential study

Most of literature on language has shown how different word-classes activate distinct neural networks within linguistic cortical areas. The present investigation aimed to demonstrate that, by means of slow evoked potentials and using the same set of words in different tasks, it is possible to activate cortical networks that are spatially and temporally distinguished. Twenty healthy subjects had to evaluate, in a word pair matching session, whether two words rhymed (phonological task), were semantically related (semantic task) or were written in the same letter case (orthographic task). Slow wave amplitude was computed in three relevant time windows: the last 0.5 s of first word presentation (W1), the initial contingent negative variation (iCNV) and the terminal CNV (tCNV). During W1 and iCNV intervals, both the orthographic and the phonological tasks were left lateralized. Furthermore, the phonological task was more lateralized than the orthographic because of a greater inhibition of the right hemisphere, whereas the orthographic task was characterized by a greater bilateral posterior activation. During the tCNV, only the phonological task remained left lateralized while orthographic and semantic were bilaterally distributed. Although the use of the same set of words tends to activate widely overlapped networks, in the present research task manipulation was effective in demonstrating task dependent differences in brain lateralization. Thus, the present paradigm and the adopted tasks are especially suited for studying deficit and recovery of language in patients affected by linguistic disorders such as developmental dyslexia and aphasia.     

Localization of semantic processing using functional magnetic resonance imaging

The relationship between the functional components of language and the anatomic foci of their neural systems represents a central issue in cognitive neuroscience. Conflicting results from a number of laboratories using positron emission tomography (PET) imaging techniques have led to a significant controversy over the specific neuroanatomic sites engaged by semantic processing. We report here results of an experiment designed to address this controversy, that is, whether semantic processing activates temporal and/or frontal brain regions. In this experiment we used cognitive tasks that emphasized either semantic or phonological information processing but that were similar on both memory search and responce generation components, together with functional magnetic resonance imaging, to examine the neuroanatomic loci of lexical-semantic as opposed to phonological processing. We studied nine right-handed men performing two silent generation tasks: rhyme, and semantic category. The former focuses on word form (phonological information) while the latter focuses on word meaning (semantic information). By “phonological” we mean the process of apprehending the sound structures of language. By “semantic” we mean information about the word's contextually specified meanings. Semantic processing makes demands on, and activates widespread areas within, brain including the inferior frontal regions bilaterally and the left posterior temporal region. Phonological processing engages a more restricted neuroanatomic assembly involving primarily anterior left temporal lobe sites. © 1995 Wiley-Liss, Inc.     

Mechanisms of writing]

Writing impairments are caused by various different mechanisms and lesions. The left posterior inferior temporal lobe plays the important role in retrieving the morphograms of the characters. Therefore the lesions involving this region have more effect on Kanji (Japanese morphogram) than on Kana (Japanese phonogram). The angular gyrus is considered to maintain the retrieved letter/character information and convert the naive information into writing performance. Sometimes Kana dominant impairment is detected due to this lesion because in some persons may have the direct route from phonemic presentation into writing execution process without definite retrieval of its form or morphology. The left superior parietal lobule is associated to the writing execution, thus, the lesion in this region induces the impairment of writing stroke and ill-shaped characters. The posterior part of the left middle frontal gyrus is related to select and arrange the letters to make a word, so the lesion in this area will develop paragraphia, in particular replacement of the letters within a word. Recently, the typing of the keyboard is becoming more popular in our everyday life. Reflecting this phenomenon, specific typing impairment called dystypia is reported. It is supposed that there is the impairment between linguistic process and typing execution.     

Auditory evoked potentials to verbal stimuli in healthy,aphasic, and right hemisphere damaged subjects

Summary Acoustic evoked potentials to meaningful words were recorded in healthy, aphasic, and right hemisphere-damaged subjects under four conditions: monaural left and right, binaural, and dichotic stimulation. Four major findings emerged. First, healthy and brain-damaged subjects differed in amplitude and latency values of the N1 and P2 components. In healthy subjects N1 was greater and P2 smaller than in aphasics. Both components peaked earlier in patients than in normals. Second, evoked potentials of healthy subjects showed a late sustained component which was decreased in aphasics. Third, the latencies of P1 and N1 as well as the amplitude of N1 showed a pathway effect, i.e. shorter latency and greater amplitude to contralateral stimulation. Fourth, under the dichotic condition, P1 and N1 peaked earlier over the left hemisphere. The N1 amplitude behaved differently in the three groups depending upon stimulating conditions.It is suggested that these differences reflect linguistic coding and related attentional processes in patients and normals.The paper was read in part on the 25th annual meeting of the German EEG Society, Würzburg, October 15 to 18, 1980, and the 24th annual meeting of the Hungarian EEG Society, Debrecen, November 4 to 6, 1980     

Variability of right hemisphere activation during semantic word processing in aphasic patients: an electrophysiologic study in three patients

After stroke, the interhemispheric reorganisation of the neural network implicated in language is hypothesized to be a function not only of the site of lesion but also of the residual impairment. With a multiple case approach, we tested this hypothesis in three chronic aphasic patients. Two patients, GE (capsulo-lenticular stroke) and JHN (fronto-temporal stroke) showed formal residual semantic difficulties, while the third patient (EG, large sylvian lesion) did not. Brain electric activity was analysed during a categorisation task of tachistoscopically presented words in the left and the right visual field. The temporal analysis of brain activity showed that both patients with semantic residual difficulties activated the right hemisphere (RH) during some steps of word processing. In the third patient, without semantic impairment, the RH was activated only during a short time period. Further more, RH activation was shown to be dependent on the visual field of word presentation. Phonological impairment was not predictive of RH activation. These results suggest that RH activation, particularly anterior regions, can occur during semantic processing of words as a function of semantic residual impairment.     

Reduction in cerebral activation after right hemisphere stroke

Destruction or disconnection of specific neuronal structures or failure to activate those structures may impair brain function. Because the right hemisphere seems dominant for mediating arousal, which is an important determinant of the capacity for cerebral activation, we predicted that subjects with right hemisphere damage would have a greater reduction in the capacity for cerebral activation than subjects with left hemisphere damage. A paradigm requiring that two simple tasks be performed singly and simultaneously was used to assess the capacity for activation. Subjects with right hemisphere damage had significantly greater impairment in the capacity for cerebral activation than subjects with left hemisphere damage. This impairment may partly explain the associations between right hemisphere damage and decreased ability to perform certain analytic and linguistic tasks.     

Age and evolution of language area functions. A study on adult stroke patients

This study attempted to verify some of the hypotheses advanced to explain the repeatedly reported finding that non-fluent aphasics are younger than fluent aphasics. One hundred and ninety eight vascular patients with cerebral infarcts documented by CT-scan were investigated. Also in this sample fluent patients were older than non-fluent patients. Age was found not to differ according to lesion site (anterior versus posterior). Patients with extensive lesions were, on average, younger than those with more restricted damage. The most interesting finding was that more than half patients with anterior lesion had fluent aphasia and that were remarkably older than anterior patients presenting with the classical non-fluent picture. It is inferred that anterior language areas undergo some kind of progressive functional evolution with age, though not in the sense postulated by Brown and Jaffe.     

Effect of number of syllables in word repetition]

We report a case of non-fluent conduction aphasia. The patient was a 59-year-old right-handed male. He suffered from aphasia after a left internal carotid artery occlusion. MRI study revealed subcortical lesions in the left inferior frontal gyrus and cortical lesion in the anterior part of the left insular gyrus and the left postcentral gyrus. The patient showed good comprehension of words and daily conversation but had a common difficulty in the following tasks; naming of pictures, repetition of words, reading of kanji and kana letters. In these tasks, the phonological output of the patient contained many literal paraphasias and there was a tendency that errors appeared more in the posterior portion of a target word. We analyzed the position of errors in the target word on word repetition tasks. The result confirmed the above observation. We speculate that the length of a target word may have played a critical rote in this patient's repetition capability.     

Adolescent developmental change in topography of EEG amplitude.

EEGs were recorded from 32 channels in 30 normal males, ages 16-22. Delta activity decreased throughout this age range. This decrease was greatest in the left frontal and temporal regions; no occipital lead showed this pattern. Relative EEG amplitude analysis, based on normalized maps, revealed decreases with age across alpha, delta, and theta bands with beta staying the same or increasing. These changes were greatest in the left temporal and left frontal regions. Taken together, these findings suggest that these cortical areas are maturing in the second decade of life. Both delta and theta showed significantly greater decreases with age in the left parietal region than in the right.     

The impact of low-grade brain tumors on verbal fluency performance

Verbal fluency has traditionally represented left hemispheric function, based on large acquired lesion studies. However, recent functional imaging studies have demonstrated bilateral hemispheric activation during phonemic and semantic word generation tasks. We examined 25 left hemisphere (LH) and 26 right hemisphere (RH) low-grade brain tumor patients on semantic and phonemic fluency. Patients were also assigned to a combined posterior (left and right) group (n = 26) or a combined posterior (left and right) group (n = 20) and compared with normal controls (NC; n = 57). We hypothesized that there would be greater left than right hemispheric phonemic and semantic fluency impairments. We also hypothesized that there would be greater anterior, specifically left anterior, than posterior impairments on phonemic fluency given their respective retrieval and initiation requirements. Finally, it was predicted that the LH patients, particularly the left posterior group, would exhibit the greatest semantic fluency impairments. Results indicated that on semantic fluency, the LH group produced significantly fewer semantic fluency responses compared to the RH group, but the expected left posterior and left frontal group differences were not found. There were no significant patient group differences associated with phonemic fluency. While we encountered semantic fluency impairments in this brain tumor population, we did not find the extensive deficits associated with the distinct or localized brain regions previously reported in the literature.     

The role of the left mesial frontal cortex in fluent speech: Evidence from a case of left supplementary motor area hemorrhage

This study reports on a woman who suffered left anterior cerebral artery hemorrhage with a focal lesion undercutting the left supplementary motor area. After almost complete recovery of language the patient was left with dysfluent, halting speech. In a series of four experiments we examined the major factors influencing the patient's articulation. There was a significant effect of lexicality and syllabic length on repetition and articulatory learning (Experiments 1 and 2). The number of syllables was also found to influence, in a simple reaction task, onset latencies, but not inter-response times (Experiment 3). On the contrary, articulatory intricacy had no particular effect on either repetition or vocal reaction (Experiments 1 and 3). While repetition of real words was preserved, single word production in word generation tasks was impaired. Rhyme generation and alliteration. both of which rely on phonological processing, were particularly involved, whereas semantic word generation tasks like verb generation and generation of category members were relatively spared (Experiment 4). Control tasks revealed that the observed phonological processing deficit was confined to the condition of generating spoken language output. These experimental findings suggest that the patient's dysfluent speech could neither be attributed to a deficit of linguistic processing proper, nor to one of motor execution. Her speech disorder rather resulted from an impairment of initiating sequential articulations, particularly in association with the process of downloading temporarily stored multisyllabic strings from an articulatory buffer. This deficit could obviously be overcome in real word repetition through the use of a semantic lexical route.     

Quantitative EEG findings in different stages of Alzheimer's disease.

Although quantitative EEG (q-EEG) has been used in Alzheimer's disease (AD), q-EEG changes in AD are complex because of the progressive nature of this disease. The topographical spectral power and occipital peak frequency (OPF) were compared among elderly controls, patients with mild cognitive impairment (MCI), and patients with four stages of AD. In AD patients, except those with a Clinical Dementia Rating Scale (CDR) score of 0.5, OPF was lower than that of elderly controls. Compared with elderly controls, the left anterior alpha spectral power was reduced in CDR 0.5; both posterior theta spectral powers were increased and all alpha spectral powers were reduced in CDR 1; all alpha and beta spectral powers were reduced and theta spectral power was increased in CDR 2; and all alpha and beta spectral powers were reduced and all delta and theta spectral powers were increased in CDR 3. Patients with MCI exhibited a reduction in both centrotemporal, posterior delta and left anterior, centrotemporal theta fields. The Mini-Mental State Examination (MMSE) score was related to left OPF, right posterior delta and left anterior theta spectral power, in that order. This study suggests that q-EEG in MCI shows nonoverlapping features between controls and AD patients, and AD patients show dynamic changes as the disease progresses. Finally, the left OPF is the parameter most significantly correlated with MMSE score.     

Phonological processes and phonemic paraphasias

Abstract

Aphasic phonological errors have received considerable attention in the literature. Linguistic analysis of phonological production errors has been largely based on the distinctive feature framework. Phonological process analysis has been demontrated to be an effective approach in child phonology. Process analysis focuses on the strategies which result in phonological error, rather than on the error itself. Few studies have attempted to apply process analysis to the phonological errors of adult aphasics. This paper applies process analysis to the phonemic paraphasias of posterior lesion aphasics from six published studies. Clinical and research implications are presented.     

Disorders of calculation in aphasic patients--spatial and verbal components

The aim of the study is to investigate whether the disorders of calculation observed in patients with Broca's aphasia are due to linguistic factors whereas those observed in patients with Wernicke's aphasia may be reduced in part to a disorder in the ability of spatial visualization. Two sets of arithmetic tasks were given to 20 Broca's aphasics, 20 Wernicke's aphasics, 20 patients with right hemispheric retrorolandic cerebral lesions and 40 patients with no brain damage. The solution of the tasks required different degrees of spatial visualization. The statistical evaluation of the data showed, as hypothesized, that Wernicke's aphasics perform significantly poorer than Broca's aphasics in tasks with a more pronounced spatial component than in the tasks having a predominantly verbal component.