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Biomedical subjects

E Lettich

Publications and source records attributed to E Lettich.

At least 37 records · Page 2Linked to original sources
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↗
PubMed1988

Neuronal activity in human lateral temporal cortex related to short-term verbal memory, naming and reading.

Extracellular microelectrode recordings were obtained from lateral temporal cortex that was subsequently resected in patients undergoing craniotomies under local anaesthesia for treatment of medically intractable epilepsy. During these recordings patients performed visually presented measures of overt and silent naming and word reading, short-term verbal memory and a control task requiring matching of angles. These measures were designed so that the same visual stimuli elicited language, short-term memory or spatial responses. Statistically significant changes within and between these various measures were identified. Technically satisfactory recordings were obtained from 17 populations reflecting activity predominantly from 1 neuron, in 13 patients. Two populations demonstrated no significant changes in any measured functions. Only 1 population showed changes suggesting a relation to visual perception. Four populations in or adjacent to the superior temporal gyrus altered activity with overt speech. Four other populations in the anterior temporal lobe altered activity during silent, but not overt speech. Some relation to language or memory was established for 13 of the 17 populations: 1 altered activity during reading alone, 6 during memory alone, and 6 to both. Most of the recording sites showing these language and memory changes were not essential for those functions based on surface electrical stimulation mapping. Thus the area of temporal lobe that participates in language and memory, as indicated by changes in neuronal activity, is substantially larger than the areas essential for those functions as determined by stimulation mapping. Within that participatory area, changes related to language were most often an increase in activity sustained throughout the task, a pattern suggestive of mechanisms of selective attention. Changes related to memory most often included a sustained increase in activity at the time of entry of information into memory, and again at retrieval, with decreased activity during the time the memory was stored. A few neuronal populations demonstrated relative inhibition of activity during the memory task, compared with control measures.

Electric Stimulation↗
PubMed1984

Cochlear summating potential recorded from the external auditory meatus of normal humans. Amplitude-intensity functions and relationships to auditory nerve compound action potential.

The summating potential (SP) and the auditory nerve compound action potential (AP) of the electrocochleogram were recorded from the external auditory meatus (EAM) of 10 normal subjects in response to alternating rarefaction and condensation clicks at 90-120 dB pe SPL. Both logarithmic and power functions suggested a similar strength of relationship between SP amplitude and stimulus intensity in each subject. However, a power function represented a more appropriate model of this relationship for the whole set of subjects than did the logarithmic function. Individual power function exponents varied from 0.35 to 0.56 with a weighted average of 0.46 and a S.E. of 0.03. By contrast, because of major heterogeneity of individual slopes at the high stimulus intensities eliciting EAM-measurable SPs, neither the logarithmic nor the power model provided a common description of the relationship between AP voltage and click strength for all subjects. Remarkable inter-individual variability also characterized the relationships between SP and AP amplitudes at various intensity levels and between the SP/AP amplitude ratio and click intensity. The lawful behavior of SP amplitude with varying click strength indicates that, in appropriate circumstance, non-invasive recordings from the ear canal of normal humans provide quantitative information on certain states of activity of cochlear receptors.

Action Potentials↗
PubMed1984

Subdural strip electrodes for localizing epileptogenic foci.

Surgical removal of epileptogenic brain is indicated for treatment of many medically refractory focal seizure disorders. One of the important factors in providing good results from surgery is the accuracy of identifying the epileptogenic focus. However, accurate localization may be difficult when only standard scalp recordings are used. Many epilepsy centers have used intracranial recording techniques to better define regions of cortical epileptogenicity . Although subdural strip electrodes were first utilized many years ago, the more popular method of intracranial recording has been by intracortical depth electrodes. The authors present their method of placing subdural strip electrodes for extensive recordings from the cortex. To date, this method has been used to provide continuous monitoring of the electrocorticogram in 28 patients for periods up to 3 weeks, with only two minor complications. This procedure is relatively safe and a valuable alternative to placing intracortical depth electrodes.

Cerebral Cortex↗
PubMed1980

Case report: responses to stripe width changes and to complex gratings of a patient with pattern-sensitive epilepsy.

A pattern-sensitive subject's ability to see faint gratings of several different stripe widths (spatial frequencies) was essentially normal, with the greatest sensitivity occurring for gratings with 2 cycles of light and dark stripes per degree of visual arc (c/deg). Epileptiform discharges, however, occurred maximally at a narrower stripe width, 5 c/deg. The 50% bandwidth of the epileptic response was approximately one octave, which is similar to postulated 'spatial frequency channels' in the visual system. Hypothesized inhibitory interactions between the 5 c/deg grating and a 15 c/deg grating were not observed.

Adult↗
PubMed1980

Pattern-sensitive epilepsy. I: A demonstration of a spatial frequency selective epileptic response to gratings.

Rare individuals suffer epileptic seizures when they view certain images, particularly stripes. Contrast-threshold functions (the ability to see faint stripes of various widths) were determined for two pattern-sensitive brothers, and the epileptogenicity of various patterns was assessed for one of them. Sine wave grating contrast-detection thresholds for the two subjects were essentially normal, with lowest thresholds at approximately 2 cycles/degree (c/deg). Epileptiform discharges occurred maximally at 5 c/deg with a 1-octave 50% bandwidth. Pattern epileptogenicity was increased by the addition of a third harmonic sine wave grating to its fundamental, but was unaffected by the phase relation of the two gratings. The frequency selectivity of epileptic responsiveness was quantitatively similar to a "spatial frequency channel." Inhibitory interaction were not present. The findings suggest relations between the phenomena of pattern-sensitive epilepsy and hypothesized spatial frequency channels which merit further exploration.

Adolescent↗
PubMed1980

Pattern-sensitive epilepsy. II: Effects of pattern orientation and hemifield stimulation.

The majority of pattern-sensitive epileptics described in the literature have responded mainly to veritical or near-vertical gratings. In this study, orientation selectivity was reexamined in two patients and the effects of hemifield stimulation are also reported. Prior studies of our subjects by Chatrian et al. (1970) revealed that Case 1 was sensitive to all orientations and that Case 2 was responsive to vertical or near-vertical gratings only. Upon reexamination, Case 1 was distinctly less sensitive to oblique orientations and Case 2 was slightly responsive to horizontal gratings. At the time of testing, Case 1 was clinically improved and Case 2 was acutely worse compared to their conditions during the 1970 studies. With low-contrast gratings, Case 1 responded only to vertical orientations. However, when presented with a checkerboard pattern, he responded only when the edges were diagonal and not when they were vertical and horizontal. Upper hemifield gratings were epileptogenic, whereas lower hemifield presentations were almost ineffective. Lateral hemifield presentation produced discharges mainly in the contralateral hemisphere. The results suggest that orientation selectivity is not a fixed property of the pattern-sensitive condition. Instead, it is apparently influenced by clinical status and pattern properties. The checkerboard results suggest that the epileptogenic feature of the pattern is its Fourier fundamental component rather than individual lines and edges. The hemifield results may indicate a functional difference between the upper and lower visual fields.

Adolescent↗
PubMed1975

Congenital insensitivity to noxious stimuli.

Cerebral-evoked potentials were used to study a 25-year-old man, the older of two siblings with congenital insensitivity to all noxious stimuli, gross impairment of temperature perception, and anhidrosis. Electrical stimulation of tooth pulp consistently eliciting pain and cerebral responses in normal subjects evoked neither cerebral potentials nor painful or other sensations in our patient. However, ordinarily painful electric shocks to the skin of his face evoked cerebral responses as well as sensations lacking disagreeable qualities. Those cerebral potentials elicited by electrical stimulation of the median nerve, clicks, and light flashes were within normal limits. These findings strongly suggest that a defect in transmission of noxious impulses presumably involving first order sensory neurons exists in our patient.

Adult↗
PubMedDate not supplied

Changes in power and coherence of brain activity in human sensorimotor cortex during performance of visuomotor tasks.

Electrocorticograms (ECoG) were recorded using subdural grid electrodes in forearm sensorimotor cortex of six human subjects. The subjects performed three visuomotor tasks, tracking a moving visual target with a joystick-controlled cursor; threading pieces of tubing; and pinching the fingers sequentially against the thumb. Control conditions were resting and active wrist extension. ECoGs were recorded at 14 sites in hand- and arm-sensorimotor area, functionally identified with electrical stimulation. For each behavior we computed spectral power of ECoG in each site and coherence in all pair-wise sites. In three out of six subjects, gamma-oscillations were observed when the subjects started the tasks. All subjects showed widespread power decrease in the range of 11-20 Hz and power increase in the 31-60 Hz ranges during performance of the visuomotor tasks. The changes in gamma-range power were more vigorous during the tracking and threading tasks compared with the wrist extension. Coherence analysis also showed similar task-related changes in coherence estimates. In contrast to the power changes, coherence estimates increased not only in gamma-range but also at lower frequencies during the manipulative visuomotor tasks. Paired sites with significant increases in coherence estimates were located within and between sensory and motor areas. These results support the hypothesis that coherent cortical activity may play a role in sensorimotor integration or attention.

Epilepsy↗
PubMedDate not supplied

Seizures of fronto-orbital origin: a proven case.

Distinguishing characteristics of seizures of frontal origin have not been clearly delineated. We describe a case of seizures of proven fronto-orbital origin to provide further definition of characteristics of seizures arising in that lobe. A 36-year-old man had medically intractable seizures since age 8 years. Clinically the seizures were stereotyped, with cessation of activity followed by turning of head and body to the right and then by struggling, kicking, and vocalizations indicating fear. Total seizure duration was approximately 30 s, with an apparent abrupt return of consciousness. The interictal scalp EEGs were similar to those of primary generalized epilepsy, with bisynchronous though asymmetric epileptiform activity anteriorly. Ictal scalp recordings were not localizing. Recordings from bilateral frontal and temporal subdural electrodes showed an electrical focus in the right fronto-orbital region which was confirmed by electrocorticography (ECoG) at the time of craniotomy. The right fronto-orbital cortex was resected and on pathologic examination showed gliotic tissue and intracytoplasmic neuronal inclusions of periodic acid-Schiff (PAS)-positive granules consistent with lipofuscinosis. The patient has remained seizure-free for 6 years after operation.

Adult↗