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G Ojemann

Publications and source records attributed to G Ojemann.

16 recordsLinked to original sources
PubMed1999

Functional roles of Broca's area and SMG: evidence from cortical stimulation mapping in a deaf signer.

The importance of the left hemisphere in language function has been firmly established and current work strives to understand regional specializations within the perisylvian language areas. This paper reports a case study of a deaf user of American Sign Language undergoing an awake cortical stimulation mapping procedure. Patterns of sign errors accompanying electrical stimulation of Broca's area and the supramarginal gyrus (SMG) are reported. Our findings show Broca's area to be involved in the motor execution of sign language. These data demonstrate that the linguistic specificity of Broca's area is not limited to speech behavior. In addition, unusual semantic-phonological errors were observed with stimulation to the SMG; these data may implicate the SMG in the binding of linguistic features in the service of language production. Taken together, these findings provide important insight into the linguistic specificity of Broca's area and the functional role of the supramarginal gyrus in language processing.

Anomia↗
PubMed1997

Visualization-based mapping of language function in the brain.

Cortical language maps, obtained through intraoperative electrical stimulation studies, provide a rich source of information for research on language organization. Previous studies have shown interesting correlations between the distribution of essential language sites and such behavioral indicators as verbal IQ and have provided suggestive evidence for regarding human language cortex as an organization of multiple distributed systems. Noninvasive studies using ECoG, PET, and functional MR lend support to this model; however, there as yet are no studies that integrate these two forms of information. In this paper we describe a method for mapping the stimulation data onto a 3-D MRI-based neuroanatomic model of the individual patient. The mapping is done by comparing an intraoperative photograph of the exposed cortical surface with a computer-based MR visualization of the surface, interactively indicating corresponding stimulation sites, and recording 3-D MR machine coordinates of the indicated sites. Repeatability studies were performed to validate the accuracy of the mapping technique. Six observers-a neurosurgeon, a radiologist, and four computer scientists, independently mapped 218 stimulation sites from 12 patients. The mean distance of a mapping from the mean location of each site was 2.07 mm, with a standard deviation of 1.5 mm, or within 5.07 mm with 95% confidence. Since the surgical sites are accurate within approximately 1 cm, these results show that the visualization-based approach is accurate within the limits of the stimulation maps. When incorporated within the kind of information system envisioned by the Human Brain Project, this anatomically based method will not only provide a key link between noninvasive and invasive approaches to understanding language organization, but will also provide the basis for studying the relationship between language function and anatomical variability.

Brain Mapping↗
PubMed1997

Evaluation of a visualization-based approach to functional brain mapping.

We describe a method for mapping stimulation data, obtained at the time of neurosurgery for intractable epilepsy, onto a 3D MRI-based neuroanatomic model of the individual patient. The mapping is done by comparing an intraoperative photograph of the exposed cortical surface with a computer-based MR visualization of the surface, interactively indicating corresponding stimulation sites, and recording 3-D MR machine coordinates of the indicated sites. Repeatability studies were performed to validate the accuracy of the mapping technique. Six observers--a neurosurgeon, a radiologist, and four computer scientists, independently mapped 218 stimulation sites from 12 patients. The mean distance of the six locations from the mean location of each site was 2.07 mm, with a standard deviation of 1.5 mm, or within 5.07 mm with 95% confidence. Since the surgical sites are accurate within approximately 1 cm, these results show that the visualization-based approach is accurate within the limits of the stimulation maps. When incorporated within the kind of information system envisioned by the Human Brain Project, this anatomically-based method will not only provide a key link between non-invasive and invasive approaches to understanding language organization, but will also provide the basis for studying the relationship between language function and anatomical variability.

Brain Mapping↗
PubMed1993

Quantitative dendritic and spine analyses of speech cortices: a case study.

The present case study documents an unprecedented opportunity for correlative investigation of brain structure and function by quantitatively investigating the basilar dendritic systems of supragranular pyramidal cells in several cortical areas from a subject who had undergone electrical stimulation mapping 2 years prior to death. Electrical stimulation mapping results provided valuable functional information about the cortical areas removed for postmortem histological analysis. Morphometric analyses distinguished between proximal (first, second, and third order) and ontogenetically later developing distal (fourth order and above) basilar dendritic branches. In general, perisylvian language association stimulation sites (classical Wernicke's and Broca's areas) were characterized by different dendritic patterns than motor strip sites. In primary motor strip tissue blocks, proximal segments were longer than distal segments. In "higher order" elaborative cortical zones, distal segments were longer than proximal segments. Proximal segments outnumbered distal segments in primary motor zones, but the numerical difference between proximal and distal segments was reduced in the association areas. Finally, fourth order segments had significantly more dendritic spines than third order segments in all sites. These dendritic findings suggest a somewhat later ontogenetic development in classical Broca's and Wernicke's areas than in primary motor cortex.

Adult↗
PubMed1989

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.

Epilepsy↗
PubMed1989

Neuronal activity in the human lateral temporal lobe. II. Responses to the subjects own voice.

We have recorded neuronal responses in the lateral temporal lobe of man to overt speech during open brain surgery for epilepsy. Tests included overt naming of objects and reading words or short sentences shown on a projector screen, repetition of tape recorded words or sentences presented over a loudspeaker, and free conversation. Neuronal activity in the dominant and non-dominant temporal lobe were about equally affected by overt speech. As during listening to language (see Creutzfeldt et al. 1989), responses differed between recordings from sites in the superior and the middle or inferior temporal gyrus. In the superior temporal gyrus all neurons responded clearly and each in a characteristic manner. Activation could be related to phonemic aspects, to segmentation or to the length of spoken words or sentences. However, neurons were mostly differently affected by listening to words and language as compared to overt speaking. In neuronal populations recorded simultaneously with one or two microelectrodes, some neurons responded predominantly to one or the other type of speech. Excitatory responses during overt speaking were always auditory. In the middle temporal gyrus more neurons (about 2/3) responded to overt speaking than to listening alone. Activations elicited during overt speech were seen in about 1/3 of our sample, but they were more sluggish than those recorded in the superior gyrus. A prominent feature was suppression of on-going activity, which we found in about 1/3 of middle and in some superior temporal gyrus neurons. This suppression could precede vocalization by up to a few hundred ms, and could outlast it by up to 1 s. Evoked ECoG-potentials to words heard or spoken were different, and those to overt speech were more widespread.

Emotions↗
PubMed1989

Neuronal activity in the human lateral temporal lobe. III. Activity changes during music.

During open brain surgery under local anesthesia for the treatment of medically intractable temporal lobe epilepsy we have recorded neuronal activity from the lateral temporal lobe with microelectrodes while the patients listened to short pieces of music. Three groups of music were tested: A) Simple familiar or unknown classical tunes at a simple rhythm and harmony, played on piano; B) Orchestrated folk music; C) Drumming without a tune. All types of music lead to changes of neuronal discharge rate. Musical pieces of type A produced a decrease in 48% of the recordings, an increase in about 17% and had no effect in 30%. A similar distribution of effects was found during type B-music (48%, 22%, 30%, respectively). During type C, only 26% showed a decrease and 74% an increase. When music was turned off, usually the reverse change from that caused by music was seen. In addition to changes of discharge rate, a slight entrainment of activity by single, regularly appearing notes (rhythm) was seen in some neurons. A few neurons showed a change of activity related to musical phrases (activation towards the end of a 4-bar 4/4 phrase). In contrast to the effects of verbal stimuli and overt speech, the effects of music on discharge rates did not show obvious topographical differences between superior, middle and inferior temporal gyrus. They also were bilateral with no significant right-left differences.

Acoustic Stimulation↗
PubMed1989

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.

Adolescent↗
PubMed1979

Human language cortex: localization of memory, syntax, and sequential motor-phoneme identification systems.

Subdivisions of the human peri-Sylvian language cortex were derived from stimulation mapping during craniotomies under local anesthesia. Naming, reading, short-term verbal memory, single and sequential orofacial movements, and phoneme identification were tested. Sequential orofacial movements and phoneme identification were altered from the same brain sites and thus identified a common system for language production and understanding. This system surrounded a final motor pathway for speech and was surrounded by a separate short-term verbal-memory system. Between the sequential motor-phoneme identification and memory systems were sites where only naming or reading were altered, including sites related exclusively by syntax.

Adolescent↗