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PubMed1989

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.

Adult↗
PubMed2005

Visually self-induced seizures sensitive to round objects.

PURPOSE: To describe a previously unreported type of self-induced pattern-sensitive seizures in a child. METHODS: Evaluation of clinical and EEG features. RESULTS: An 18-month-old boy was initially seen with series of short focal tonic seizures self-induced by gazing intermittently at round objects. Self-induction of these seizures had an obvious relieving effect on the child. Covering the round object foiled further seizures but resulted in a tantrum. Later in the course, an increasing variety of patterns proved to be capable of inducing seizures, which occurred with increasing frequency and severity, including secondarily generalized tonic-clonic seizures. Interictal EEG revealed multifocal sharp-and-slow-waves. Ictal EEG showed no abnormalities during short focal seizures and rapidly generalizing epileptic discharges during a secondarily generalized seizure. No photosensitivity was noted. Motor and mental development of the boy stagnated over a period of 2 years. Behavioral therapy as well as medical treatment, consisting of various combinations of antiepileptic drugs (AEDs) together with a selective serotonin-reuptake inhibitor, were of merely transient benefit. Only combined pharmacotherapy, including valproate, sulthiame, and clobazam, resulted in seizure control at age 3 years 9 months. CONCLUSIONS: Visual capture of geometric patterns other than stripes or gratings may trigger focal seizures with secondary generalization. Synchronization of cortical neurons responsible for pattern recognition may account for epileptogenesis in this child.

Age Factors↗
PubMed1996

Spatial tuning loss of pattern reversal visual evoked response in optic nerve disease.

We compared the pattern reversal visual evoked response (PVER) amplitude-check size functions from 25 eyes (25 normal subjects; visual acuities > or = 20/20) with those from 32 eyes (22 patients; visual acuities 20/15 to 20/50; mean, 20/25.5) with mild optic nerve disease to determine if spatial tuning loss of the PVER occurs in the presence of optic nerve dysfunction. The steady-state PVER was recorded with five check sizes (range, 160 to 10 minutes of arc). To analyze the PVER amplitude-check size function, we calculated the difference between the maximum and minimum PVER amplitudes and then calculated the area of spatial tuning (the area under the function). Values were significantly smaller in patients than in normal subjects (1.81 +/- 1.27 microV versus 5.73 +/- 3.27 microV; F = 41.24, p = 0.0001; 3.87 +/- 2.70 area units versus 12.57 +/- 7.60 area units; F = 38.62, p = 0.0001). There was no shift in the distribution of peak check sizes. Results suggest that a spatial tuning loss occurs in optic nerve disease. The shape of the function, including the area of spatial tuning, appears to be a sensitive indicator of early or mild optic nerve dysfunction.

Adolescent↗
PubMed1982

Pattern reversal visual evoked potentials in Japanese patients with multiple sclerosis.

Forty-seven Japanese patients with multiple sclerosis, 29 probable (clinically definite) and 18 possible, were studied by black-and-white checkerboard pattern reversal visual evoked potential and were compared with a control group of 20 healthy young adults. The major positive peak (P100) was found to be abnormal in 70% of all cases, 90% of probable cases and 39% of possible cases. P100 was delayed in 38% of all cases and was absent in 23% of all cases. None of the eyes showing a flat pattern response was in the acute stage of optic neuritis. The percentage of cases with no response (23% of all cases) was greater than any of the previously reported series from Western countries, substantiating the previously reported clinical features of oriental multiple sclerosis. The pattern response was absent only when testing eyes with severe visual impairment, whereas delayed latency of P100 was seen regardless of the severity of visual impairment, suggesting the usefulness of P100 latency for detecting subclinical optic nerve lesions.

Adolescent↗
PubMed1994

Effects of aging on the primate visual system: spatial and temporal processing by lateral geniculate neurons in young adult and old rhesus monkeys.

1. Visual abilities decline during normal aging, and many of these declines are due to neural changes in the retina or central visual pathways. We have begun studies of the primate visual system to investigate the location and nature of these changes as well as to answer general questions about the effects of aging on neural function. We began with the dorsal lateral geniculate nucleus (LGN) because it is the main structure through which visual information passes on the way to cortex and because the parallel parvocellular and magnocellular pathways, which may be affected differently by aging, are anatomically distinct there. 2. Single-cell recordings were made in the LGN of young adult (5-16 yr) and old (25-28 yr) rhesus monkeys. We made quantitative measures of a wide variety of response properties for a large number of parvocellular (n = 257) and magnocellular (n = 113) neurons in the two groups of animals. As a result, in addition to studying the effects of aging, we were able to make quantitative comparisons between parvocellular and magnocellular neurons using larger samples than have been studied previously and for some properties that have not been studied before. 3. We found that magnocellular neurons have significantly higher maximal response rates and signal-to-noise ratios than parvocellular neurons. However, response latencies to visual stimulation were similar for neurons in the two types of layers. In agreement with previous studies, magnocellular neurons had higher maximal contrast sensitivity and higher contrast gain than parvocellular neurons. However, the sensitivity difference occurred because nearly all of the neurons with low sensitivities (< 10) were in the parvocellular layers, not because neurons in the magnocellular layers had the highest sensitivities. 4. Neurons with the smallest receptive-field centers, the highest spatial-frequency resolutions, and the highest optimal spatial frequencies were found in the parvocellular layers. However, the overall distributions of each of these properties overlapped substantially for neurons in the two types of layers, and the mean values were not significantly different. The mean high temporal-frequency cutoff was significantly higher for magnocellular than parvocellular neurons, but the difference was small (only 3 Hz), and it occurred because many parvocellular neurons had lower cutoffs than any seen in the magnocellular layers, not because magnocellular neurons had the highest temporal-frequency cutoffs. Parvocellular neurons also had narrower temporal-frequency tuning than magnocellular neurons. However, there was no significant difference in optimal temporal frequency.(ABSTRACT TRUNCATED AT 400 WORDS)

Aging↗
PubMed2003

Functional specialization in the human frontal cortex observed during task anticipation.

The purpose was to evaluate whether a scalp-recorded slow potential will show specificity during the anticipation of different types of visual tasks. One of the tasks required the comparison of pairs of familiar faces, and the other was the comparison of abstract dotted patterns. Each trial began with one of the two cues (S1) followed by consecutive pictures (S2 and S3). Faces and patterns were superimposed, and the switching between tasks depended on the cue. The ERP analysis was done for the time window between S1 (cue) and S2 presentations. The major differences between tasks were found in the anterior scalp regions starting at 700 ms from S1 onset. During Pattern task anticipation, the proposed sources in the right frontal area were more anterior, inferior and lateral than those in Face task. The task-specific slow electric potentials may indicate the functional specialization for attentive anticipation in the human frontal lobe.

Adult↗
PubMed1989

Neurophysiological investigation of the pretectal nucleus lentiformis mesencephali in Rana pipiens.

Previous studies have demonstrated that the large-celled, optic pretectal nucleus lentiformis mesencephali (nLM) is essential for horizontal optokinetic nystagmus, yet little is known about its neurophysiology. In the present study, single-unit analysis of nLM utilized a large-field, patterned stimulus presented for 8 directions and 3 velocities of movement. All units localized in nLM were spontaneously active, motion sensitive, with response profiles that ranged from strongly directional and narrowly tuned to asymmetric and broadly tuned. Only about one-third of the units could be classified as directional, and no response bias for horizontal or temporal-to-nasal motion was observed. The majority of directional units showed greatest responsiveness at the lowest stimulus velocity, while the reverse occurred for many broadly tuned units. These low-velocity, highly directional units may be comparable to the 'retinal slip' neurons recently described in the large-celled pretectal nucleus of mammals. Directional information in the nLM of Rana pipiens thus appears to be represented in the activity of a large population of motion-sensitive units which includes both narrowly and broadly tuned individual response profiles. These results are consistent with the population-coding hypothesis recently advanced to account for directional coding in other sensorimotor systems, including primate motor cortex and superior colliculus.

Acceleration↗
PubMed2005

Phonotactic knowledge and lexical-semantic processing in one-year-olds: brain responses to words and nonsense words in picture contexts.

During their first year of life, infants not only acquire probabilistic knowledge about the phonetic, prosodic, and phonotactic organization of their native language, but also begin to establish first lexical-semantic representations. The present study investigated the sensitivity to phonotactic regularities and its impact on semantic processing in 1-year-olds. We applied the method of event-related brain potentials to 12- and 19-month-old children and to an adult control group. While looking at pictures of known objects, subjects listened to spoken nonsense words that were phonotactically legal (pseudowords) or had phonotactically illegal word onsets (nonwords), or to real words that were either congruous or incongruous to the picture contents. In 19-month-olds and in adults, incongruous words and pseudowords, but not nonwords, elicited an N400 known to ref lect mechanisms of semantic integration. For congruous words, the N400 was attenuated by semantic priming. In contrast, 12-month-olds did not show an N400 difference, neither between pseudo- and nonwords nor between incongruous and congruous words. Both 1-year-old groups and adults additionally displayed a lexical priming effect for congruous words, that is, a negativity starting around 100 msec after words onset. One-year-olds, moreover, displayed a phonotactic familiarity effect, that is, a widely distributed negativity starting around 250 msec in 19-month-olds but occurring later in 12-month-olds. The results imply that both lexical priming and phonotactic familiarity already affect the processing of acoustic stimuli in children at 12 months of age. In 19-month-olds, adult-like mechanisms of semantic integration are present in response to phonotactically legal, but not to phonotactically illegal, nonsense words, indicating that children at this age treat pseudowords, but not nonwords, as potential word candidates.

Acoustic Stimulation↗
PubMed1990

Allocation of visual attention to spatial locations: tradeoff functions for event-related brain potentials and detection performance.

Event-related brain potentials (ERPs) were recorded in response to unilateral arrays of letters flashed in rapid, randomized sequences to left and right visual field locations. Subjects were required to focus attention exclusively on either left or right field stimuli, or to divide attention in different proportions between the two fields, with the aim of detecting infrequent target letters. Both d' and percent hits for target detections increased significantly as attentional allocation to a stimulus location increased. Attention operating characteristic (AOC) curves for the target detection scores were highly similar in form to those for the amplitudes of the long-latency, endogenous ERP components--N350-650 and P400-800 (P300). All of these measures showed gradual, nearly rectangular tradeoff functions. In contrast, the AOC curves for the early sensory-evoked components displayed steep, nearly linear amplitude tradeoffs as attention was increasingly allocated to one visual field at the expense of the other. The early and late ERP components were considered as indices of separate but interacting levels of attentional selection having different operating principles.

Adolescent↗