Anterior Electrodes Research Articles

Event-related potentials during memory search and selective attention to letter size and conjunctions of letter size and color.

The analysis of event-related potentials was used in two experiments to investigate the structure of information processing in a task in which subjects selectively attended to letter size (Experiment 1) or a conjunction of letter size and color (Experiment 2) and searched for target letters within the attended stimulus category. The event-related potentials showed that selective attention to letter size resulted in the enhancement of a central N2b component (onset about 200 ms), which was assumed to reflect feature nonspecific orienting of attention. When attention was directed to conjunctions of letter size and color an earlier effect was found (onset about 150 ms) consisting of positivity at the anterior electrodes and negativity at OZ. This earlier effect was assumed to reflect feature-specific selective processing. Although the early effect showed a hierarchical pattern of results, in which the effect of attending to size was contingent on the relevance of the color attribute, the N2b showed a more independent pattern of results, in which the relevance of either the color or the size attribute resulted in an enhancement of this component, independent of the relevance of the other attribute. An increase in the duration of the memory search process resulted in a prolonged negativity with an onset of about 200 ms which was maximal at CZ. In both experiments the initial phase of this negativity was also found in the event-related potentials to the unattended stimulus categories, suggesting that the search process was initiated nonselectively and terminated after the selection cues were identified. Detection of attended target letters resulted in a parietal P3b component. In both experiments there was an earlier effect discriminating targets and nontargets in the range 200-300 ms.

Brain potentials during selective attention, memory search, and mental rotation.

Event-related potentials were measured in a task that combined the classic selective attention paradigm with memory search and mental rotation paradigms. Subjects were required to attend to stimulus letters in one color and to ignore stimuli in a different color. Within the attended category subjects searched for target letters from a prememorized set (the memory set) and indicated whether they were presented normally or in mirror-image. Letters in all stimulus categories were presented randomly in either their upright position or rotated over 60 degrees, 120 degrees, or 180 degrees. The event-related potentials showed that the earliest effect of attending to color was a positivity at the anterior electrodes and a negativity at Oz (onset about 150 ms), followed by the enhancement of a central N2 component (N2b, onset about 220 ms). The early effect is thought to reflect selective processing of elementary stimulus features, the later N2b the covert orienting of attention. A later, prolonged central negativity elicited by attended stimuli covaried with the duration of the memory search process. Target detection resulted in a parietal P3b component, and also in an earlier negativity (in the range approximately 200-300 ms) to both attended and unattended targets, suggesting an early preattentive target classification. There were two effects of the rotation of stimuli. First there was an early occipital effect (about 200-300 ms), irrespective of attention and stimulus categories. It was argued that this effect reflected the preattentive identification of the orientation of the stimulus letters. A later (onset about 350-400 ms) parietal effect consisted of an increase in negativity as a function of the angle over which letters were rotated. This prolonged negativity had a later onset latency than the search-related negativity, and was restricted to the event-related potentials to target letters in the attended input channel. It was suggested that this component is the manifestation of a mental rotation process. It was argued that rotation-related negativity and memory search-related activity reflect operations in distinct working memory subsystems.

The Anterior Temporal Electrode in the EEG of the Adult: Utility and Optimal Placement

ABSTRACT.The anterior temporal cerebral region is not well covered, electroencephalographically, by the usual EEG electrodes. Numerous attempts have been made to add anterior temporal electrodes. There has been discussion regarding the amount of additional information actually attributable to those electrodes. We systematically evaluated the abnormalities revealed by one such noninvasive set of anterior temporal electrodes, D. Silverman's T1 and T2. We reviewed 624 consecutive EEGs and concluded that, in the adult, anterior temporal electrodes can add significantly to the information contained in the routine interictal EEG.

Comparison of Sphenoidal and Anterior Temporal Electrodes in Recording Epileptiform Activity from Patients with Medial Temporal Lobe Epilepsy

Comparison of Sphenoidal and Anterior Temporal Electrodes in Recording Epileptiform Activity from Patients with Medial Temporal Lobe Epilepsy

Time course of sympathetic denervation supersensitivity in canine ventricular recovery

We studied the timing of the electrophysiological effects of sympathetic supersensitivity with chronically implanted electrodes in the anterior and posterior left ventricular free wall in 10 dogs. We produced denervation of the anterior wall in six dogs by application of phenol surrounding the anterior electrode. Drug infusions that were performed under pentobarbital sodium anesthesia included norepinephrine, isoproterenol, and methoxamine. In four controls there was no difference in response of the two sites. Presynaptic supersensitivity was manifest as early as 2 days and as late as 64 days by a parallel left shift (greater than or equal to 8.3 ms) in the norepinephrine dose to effective refractory period shortening response curve in the anterior compared with posterior left ventricle, P less than 0.01. The isoproterenol dose-response curve was also shifted to the left by 5.6 ms (P less than 0.01) but was manifest only after 10 days and only until 28 days from the denervation procedure. Local repolarization in the denervated areas shortened more than the innervated areas with both drugs. The methoxamine dose-response curve was flat, and the anterior-denervated area was not different than the posterior-innervated area. We conclude that recovery properties in ventricular muscle demonstrate evidence of supersensitivity, which is neurotransmitter and beta- but not alpha-receptor specific.

The role of intrinsic neurons in lateral hypothalamic self-stimulation

In this brief review, we summarize some of our recent work concerning the effect of a specific lesion of the intrinsic neurons located in the middle part of the lateral hypothalamus on electrical self-stimulation of this structure by electrodes implanted along the medial forebrain bundle. In a first experiment the neurons of the lateral hypothalamus were destroyed unilaterally by local injejction of ibotenic acid (4 μg in 0.5 μl). The contralateral side served as the sham-lesion control. Between 10 and 20 days later, electrodes were bilaterally implanted, one in the lesioned area, the other in the contralateral hypothalamus. Intracranial self-stimulation (ICSS) was obtained separately for each electrode, at various current intensities, using a nose-poke response. ICSS from electrodes implanted in the lesioned area was decreased in all cases, whereas ICSS of the sham-lesioned side was normal. In a second experiment, two groups of rats lesioned and implanted as above, received two additional electrodes either in the anterior hypothalamus or in the posterior hypothalamus. In rats with electrodes in the anterior hypothalamus, the lesion produced a large deficit in self-stimulation when stimulation was applied to the anterior electrode ipsilateral to the lesion. Only 3 of 6 rats showed a decrease in ICSS with stimulation of the posterior hypothalamic electrode ipsilateral to the lesion. These results suggest that ICSS in the anterior part of the medial forebrain bundle is sustained by long fibers originating in the middle part of the lateral hypothalamus, while ICSS in the posterior part of the lateral hypothalamus may not depend on the neurons located in the lesioned area.

Electrical self-stimulation deficits in the anterior and posterior parts of the medial forebrain bundle after ibotenic acid lesion of the middle lateral hypothalamus

The aim of the present study was to analyse the involvement of the intrinsic neurons located in the middle lateral hypothalamus in electrical self-stimulation measured with electrodes in the anterior and posterior parts of the medial forebrain bundle. In rats without hypothalamic lesions, self-stimulation rates from both anterior and posterior electrodes were similar on either side of the brain. For all rats with ibotenic acid-induced lesions in the lateral hypothalamus, self-stimulation rates were lower with electrodes in the area of the lesion, while self-stimulation on the contralateral side was normal. In rats with electrodes in the anterior hypothalamus, the lesion produced a large deficit when stimulation was applied to the anterior electrode ipsilateral to the lesion. Only three rats showed a decrease in self-stimulation with stimulation of the posterior hypothalamic electrode ipsilateral to the lesion; self-stimulation of the other three rats was normal. These results suggest that self-stimulation in the anterior part of the medial forebrain bundle is supported by long fibers originating in the middle part of the lateral hypothalamus, while self-stimulation in the posterior part of the lateral hypothalamus can be influenced by another system not involved in reward processes observed in the rostral part of the medial forebrain bundle.

Anatomically-dependent facilitation and inhibition of hypothalamic self-stimulation by food deprivation

The effects of food deprivation on hypothalamic self-stimulation in guinea pigs were investigated in a free-operant shuttle-box situation which provides a rate-independent index of reward and an index of aversion. Food deprivation produced anatomically specific reward-modulation effects that were clearly dissociable from general activation or debilitation. All of the posterior electrodes showed increased reward and all of the anterior electrodes showed decreased reward. In contrast, food deprivation generally exerted very little effect on the aversive component of ICS.

Directionality of rewarding impulses within the medial forebrain bundle self-stimulation system of the rat.

Self-stimulation performance of rats was tested with conditioning pulses to the anterior preoptic area of the medial forebrain bundle followed at various intervals by test pulses to the contralateral posterior hypothalamic area of this bundle. Alternatively, conditioning pulses were delivered through the posterior electrode and test pulses were sent through the anterior electrode. The animals' performance in these two test sequences was indicative of (i) synaptic facilitation and (ii) a posterior convergence site of "self-stimulation impulses" in the medial forebrain bundle.

Current distribution from defibrillation electrodes in a homogeneous torso model

In this paper a theoretical model is derived and use to estimate parameters relevant to current flow from external defibrillating electrodes in the antero-posterior position. The mean current density in the heart was found to be 3.6 milliamperes/cm 2 . per ampere current through the electrodes. The ratio of the extreme values of current densities in the heart was 4 to 1 and the percentage of total current flowing through the heart 45%. A change in chest depth from 19 to 30 cm. caused a change in average density of 10 to 20% from that found in a typical chest while a 2 inch displacement of the anterior electrode resulted in a 14% change in average density in the heart. Neglecting possible effects due to poor electrode contacts, theoretically computed temparature rises associated with single pulse defibrillation were found to be negligible. The validity of the theoretical model was, tested by comparing some of its predictions to corresponding measurements in a homogeneous electrolytic tank and in human subjects. Although the correlation was good, the data must be considered approximate in view of the model simplifications. A design criterion in the form of a “quality ratio” is discussed. This is the ratio of the minimum current in the heart to the maximum current density elsewhere in the body.

The Use of the Lead-Field Concept in the Development of Leads Satisfactory for Vectorcardiography. I. The Sagittal Lead

After a brief discussion of the lead field concept and an illustration of its application using a Teledeltos paper model, studies carried out on patients, employing multiple electrode or grid arrangements located over the precordium and the left posterior chest, to obtain the sagittal component of cardiac electromotive forces (e.m.f.'s), are described. On the basis of these observations, a minimum of 15 properly arranged and connected electrodes should be employed in the anterior electrode system but fewer will be needed posteriorly. A scheme, using 63 electrodes mounted in sponge rubber, has been devised to simplify the grid arrangement.

The unipolar Leads of the electrocardiogram in right ventricular enlargement: Juan Codina-Altés, M.D., and Carlos Pijean de Beristain, M.D., Barcelona, Spain

1.1. Seven cases are reported which show huge T-waves in the precordial leads of the electrocardiogram.2.2. In all cases the large waves disappeared at a later date.3.3. These huge T-waves are sometimes clicited from a small area of the precordium only. If the anterior electrode is placed clsewhere on the anterior chest wall, they may not appear in the tracing.4.4. The symptoms in this group of cases point to the diagnosis of coronary occlusion. Their relative mildness suggests the complete occlusion of a small vessel or the partial occlusion of a large one.5.5. The lesion associated with huge upright T-waves in precordial leads is probably located in the auterior surface of the left ventricle. The fact that this clectrocardiographic phenomenon has not been seen in a series of 550 controls, makes it seem justifiable to regard it as indicative of an acute or subacute disturbance of the coronary circulation.6.6. Large inverted T-waves in precordial leads considerably exceeding the normal amplitude probably signify the presence of a lesion in the posterior surface of the left ventricle, analogous to that causing huge upright T-waves.7.7. RS-T interval deviations may be absent in this group of cases.8.8. A small upward deflection, prior to the downward deflection of QRS in precordial leads, has been observed in several of these cases. This wave is probably an abnormal finding, if more than 2 mm. in height.

Huge T-waves in precordial leads in cardiac infarction

1. 1. Seven cases are reported which show huge T-waves in the precordial leads of the electrocardiogram. 2. 2. In all cases the large waves disappeared at a later date. 3. 3. These huge T-waves are sometimes clicited from a small area of the precordium only. If the anterior electrode is placed clsewhere on the anterior chest wall, they may not appear in the tracing. 4. 4. The symptoms in this group of cases point to the diagnosis of coronary occlusion. Their relative mildness suggests the complete occlusion of a small vessel or the partial occlusion of a large one. 5. 5. The lesion associated with huge upright T-waves in precordial leads is probably located in the auterior surface of the left ventricle. The fact that this clectrocardiographic phenomenon has not been seen in a series of 550 controls, makes it seem justifiable to regard it as indicative of an acute or subacute disturbance of the coronary circulation. 6. 6. Large inverted T-waves in precordial leads considerably exceeding the normal amplitude probably signify the presence of a lesion in the posterior surface of the left ventricle, analogous to that causing huge upright T-waves. 7. 7. RS-T interval deviations may be absent in this group of cases. 8. 8. A small upward deflection, prior to the downward deflection of QRS in precordial leads, has been observed in several of these cases. This wave is probably an abnormal finding, if more than 2 mm. in height.