Differential right hemispheric memory storage of emotional and non-emotional faces

Seventy-two female subjects memorized two photographed faces and subsequently discriminated these “target” faces from two “non-target” faces. The faces were presented unilaterally for 150 msec, and manual reaction times for the discriminations served as the dependent variable. The face stimuli were either “neutral” or “emotional” in facial expression, these attributes having been shown, by a preliminary study, to be highly reliable. Faster reaction times were obtained for left visual field than for right visual presentation. Subjects (N = 36) who memorized emotional faces showed significantly faster discrimination of faces presented in the left than in the right visual field (25·7 msec); subjects (N = 36) who memorized faces lacking emotional expression also showed significant left visual field superiority (11·6 msec), but this left field superiority was significantly smaller than that of subjects memorizing emotional faces. Results are consistent with previous tachistoscopic evidence of right hemisphere superiority in face recognition speed and with diverse non-tachistoscopic evidence of preferential memory storage of affective material. The pattern of latencies for the different visual field-response hand conditions supported a model of lateral specialization in which the specialized hemisphere normally processes both directly-received and interhemispherically- transferred stimuli.     

Selective averaging of the intracerebral click evoked responses in man: an improved method of measuring latencies and amplitudes.

Individual click evoked responses recorded in the right and left frontal lobe in man have been correlated with different templates, that is, particular wave shapes of evoked responses, and from the maxima of the cross correlation functions individual estimates were obtained of amplitude and latency. Averages were then made of evoked responses having particular amplitude and/or latency values. Using such selected trials for averaging, better results were obtained and artificial amplitude damping avoided. It was found for example that the component N90 varied in latency between 75 and 100 msec and was linked with the behaviour of the contralateral recorded potential amplitude of P150. Furthermore it was found that the biphasic potential N230 P430 was very unstable in latency and the amplitude of the averaged potential using all trials was about 30% too small.     

Recovery functions of somatosensory vertex potentials in man: interaction of evoked responses from right and left fingers.

Somatosensory vertex potentials (SVPs) were examined in 12 healthy subjects in response to painful electrical stimulation of the finger. SVPs consisted of N1, P1, and N2. The average latencies of the 3 peaks were 150, 225, and 350 msec, respectively. The latency and amplitude of each potential were reproducible for each subject. Recovery functions of the SVPs were analyzed in 10 subjects. A pair of stimuli were delivered to the right or left finger with interstimulus intervals (ISIs) of 50, 100, 150, 200, 350, 500 and 650 msec. SVPs partially recovered with the shortest ISI (50 msec). Full recovery could not be obtained even with the longest ISI (650 msec). Differences in recoveries within 650 msec of ISI were not observed between right and left stimulations. To examine the interaction between SVPs evoked by right and left finger stimulation, recovery functions from prior contralateral finger stimulation were analyzed with the same ISIs. SVP recoveries for right after left or left after right patterns of stimulus delivery were nearly the same as those for ipsilateral ones. It is suggested that SVPs are generated at nearly the same site in the sensory pathway regardless of the side stimulated.     

EEG and EMG responses to emotion-evoking stimuli processed without conscious awareness

Dichotic stimulus pairs were constructed with one word that was emotionally neutral and another that evoked either negative or positive feelings. Temporal and spectral overlap between the members of each pair was so great that the two words fused into a single auditory percept. Subjects were consciously aware of hearing only one word from most pairs; sometimes the emotion-evoking word was heard consciously, other times the neutral word was heard consciously. Subjects were instructed to let their thoughts wander in response to the word they heard, during which time EEG alpha activity over left and right frontal regions, and muscle activity (EMG) in the corrugator (“frowning”) and zygomatic (“smiling”) regions were recorded. Both EEG and EMG provided evidence of emotion-specific responses to stimuli that were processed without conscious awareness. Moreover both suggested relatively greater right hemisphere activity with unconscious rather than conscious processing.     

Localization and characterization of speech arrest during transcranial magnetic stimulation.

OBJECTIVE: To determine the anatomic and physiologic localization of speech arrest induced by repetitive transcranial magnetic stimulation (rTMS), and to examine the relationship of speech arrest to language function. METHODS: Ten normal, right-handed volunteers were tested in a battery of language tasks during rTMS. Four underwent mapping of speech arrest on a 1 cm grid over the left frontal region. Compound motor action potentials from the right face and hand were mapped onto the same grid. Mean positions for speech arrest and muscle activation were identified in two subjects on 3-dimensional MRI. RESULTS: All subjects had lateralized arrest of spontaneous speech and reading aloud during rTMS over the left posterior-inferior frontal region. Writing, comprehension, repetition, naming, oral praxis, and singing were relatively spared (P < .05). Stimulation on the right during singing abolished melody in two subjects, but minimally affected speech production. The area of speech arrest overlay the caudal portion of the left precentral gyrus, congruous with the region where stimulation produced movement of the right face. CONCLUSIONS: The site of magnetic speech arrest appears to be the facial motor cortex. Its characteristics differ from those of classic aphasias, and include a prominent dissociation among different types of speech output.     

Scalp-recorded short and middle latency peroneal somatosensory evoked potentials in normals: comparison with peroneal and median nerve SEPs in patients with unilateral hemispheric lesions

Peroneal somatosensory evoked potentials (SEPs) were performed on 23 normal subjects and 9 selected patients with unilateral hemispheric lesions involving somatosensory pathways. Recording obtained from right and left peroneal nerve (PN) stimulations were compared in all subjects, using open and restricted frequency bandpass filters. Restricted filter (100-3000 Hz) and linked ear reference (A1-A2) enhanced the detection of short latency potentials (P1, P2, N1 with mean peak latency of 17.72, 21.07, 24.09) recorded from scalp electrodes over primary sensory cortex regions. Patients with lesions in the parietal cortex and adjacent subcortical areas demonstrated low amplitude and poorly formed short latency peroneal potentials, and absence of components beyond P3 peak with mean latency of 28.06 msec. In these patients, recordings to right and left median nerve (MN) stimulation showed absence or distorted components subsequent to N1 (N18) potential. These observations suggest that components subsequent to P3 potential in response to PN stimulation, and subsequent to N18 potential in response to MN stimulation, are generated in the parietal cortical regions.     

The electrophysiology of tactile extinction: ERP correlates of unconscious somatosensory processing

We examined the electrophysiological correlates of left-sided tactile extinction in a patient with right-hemisphere damage. Computer-controlled punctate touch was presented to the left, right or both index fingers in an unpredictable sequence. The patient reported his conscious tactile percept (“left”, “right” or “both”). He showed extinction on 75% of bilateral trials, reporting only right stimulation for these. Somatosensory evoked potentials for unilateral stimulation showed early components over contralateral somatosensory areas (P60 and N110) for either hand. In contrast to the results observed for age-matched controls, the patient’s P60 was smaller in amplitude for left-hand touch over the right hemisphere than for right-hand touch over the intact hemisphere. Bilateral trials with extinction revealed residual P60 and N110 components over the right hemisphere in response to the extinguished left touch. These results demonstrate residual unconscious somatosensory processing of extinguished touch. They also suggest that tactile extinction can be caused by attenuation rather than elimination of somatosensory responses in the damaged hemisphere, with an underlying deficit even on unilateral trials.     

An investigation of attentional contributions to visual errors in right "neglect dyslexia"

One type of error that is sometimes produced by patients with acquired dyslexia is the substitution of an orthographically similar word with letters that overlap the target either in early or late letter positions. When such errors affect the left sides of words, they are usually produced by patients with focal right hemisphere lesions who typically show evidence of left neglect in non-reading tasks. This pattern has thus been termed “neglect dyslexia”. When the right sides of words are affected, however, patients frequently fail to show any signs of neglect in tasks other than reading. This study presents results from a patient with left hemisphere damage, and a very clear pattern of right “neglect” errors in reading, on a series of tasks testing attentional and imagery processes. Given the magnitude and consistency of the patient's reading errors, there was little evidence that these errors resulted from inattention to the right side of space or to the right side of an internally generated visual image. It is argued that the positional errors result from an impairment to an abstract ordinal code with graded activation of letter positions from first to last, and that this code is specific to tasks involving orthographic representations.     

The effects of frontal cortex lesions on event-related potentials during auditory selective attention

We compared electrophysiological indices of auditory selective attention in control subjects and in patients with unilateral lesions of the dorsolateral frontal lobes. In control subjects, ERPs following attended tones showed an enhanced negativity from 80 to 500 msec post-stimulus which had a different topographic distribution than the N120. Lesions of the frontal lobes reduced the attention-related negativity and impaired behavioral performance. The ERP reductions were equivalent in recordings obtained from electrodes placed over the damaged and intact cortex. A difference was noted between left and right frontal groups as a function of ear of delivery of the stimuli. Patients with left frontal lesions showed reduced attention effects following tones presented to either ear. Patients with right frontal lesions showed intact attention effects to right ear tones, but no attention-related negativity to left ear tones. When the left and right frontal groups were considered together, tones in ignored channels produced larger responses when presented to the ear contralateral to damaged cortex. These results underline the important role of the frontal lobes in processes of selective attention. Although the endogenous negativity produced in selective attention tasks does not appear to originate in dorsolateral frontal cortex, the frontal lobes exhibit a modulating influence upon it. In addition, the endogenous attention related negativity and exogenous N120 components apparently arise from different neural generators.     

The second sensory area in humans: evoked potential and electrical stimulation studies

A patient with intractable seizures originating from a right frontal focus was evaluated for surgical treatment. This evaluation was carried out using a chronically implanted array of 96 stainless steel electrodes 1 cm apart and covering the perirolandic and frontal areas. Somatosensory evoked potentials and electrical stimulation of the subdural electrodes localized the primary sensory hand area. Evoked potentials of identical waveform but of lower amplitude and 2.4 ms longer latency were recorded in the inferior frontal gyrus immediately anterior to the face area of the motor strip. Electrical stimulation of that area elicited: (1) a "paralyzing" feeling in the left arm and face; (2) inhibition of rapid alternating movements of left fingers, left hand, and tongue; (3) inability to maintain a strong voluntary muscle contraction of the left hand or tongue; and (4) speech arrest. This appears to be the first report of a secondary sensory area in humans demonstrated by both electrical stimulation and evoked potential studies. Electrical stimulation showed that the secondary sensory area overlapped an area of complex motor control, suggesting that the secondary sensory area provides direct sensory feedback information for appropriate motor integration.     

Repetitive transcranial magnetic stimulation of the dominant hemisphere can disrupt visual naming in temporal lobe epilepsy patients.

We used repetitive transcranial magnetic stimulation (rTMS) to study visual naming in 14 patients with temporal lobe epilepsy. Ten had left hemisphere language by Wada testing and all experienced speech arrest with rTMS of the motor speech area in the left frontal lobe. One left-hander had speech arrest with stimulation of sites on both sides. Subjects were asked to name pictures or read words presented on a computer monitor. rTMS was delivered on half of the trials. Stimulation sites were the motor speech area in the left frontal lobe, the mirror site on the right, and the left and right mid superior and posterior temporal lobes. rTMS at left hemisphere sites caused more naming errors than did right hemisphere rTMS. All individual subjects, except two who had temporal lobe resections and the one with bilateral speech arrest, produced more naming errors with rTMS of left hemisphere sites. There was no significant effect on word reading. rTMS at the left hemisphere and right frontal sites produced reductions in reaction time for picture naming, but not for word reading. This was observed for both correct and incorrect responses. This study shows that left hemisphere rTMS can disrupt visual naming selectively.     

On hemispheric differences in evoked potentials to speech stimuli.

Eight subjects listened to lists of speech sounds (pa or ba) or pure tones (250 or 600 c/sec). Within each list one of the sounds (the "frequent") occurred more often than the other (the "target") in a ratio of approximately 4:1. Subjects were required to count the targets in each list; concurrently, evoked responses to both targets and frequents were being separately averaged from electrodes at vertex at symmetrical left and right parietal locations. The evoked responses show the expected sequence of deflections at all three electrode sites, including large P3 waves (about 350 msec latency) to the target stimuli. However, the left and right hemispheric responses to speech or tones, either frequent or target, were strikingly similar, both to the eye and by statistical tests intended to reveal differences between them.     

Cerebral somatosensory potentials evoked by posterior tibial nerve stimulation: lateralization and relation to handedness in left-handed normal subjects

Somatosensory potentials evoked by stimulation of the right and left posterior tibial nerves were studied in left-handed normal subjects. Hand preference was assessed by the Edinburgh Handedness Inventory; a laterality score (Geschwind score) was calculated for each subject. Hand skill was assessed by the peg moving task. The mean amplitude of the N1 wave from the right cerebral cortex was found to be significantly larger than that from the left cerebral cortex. In the subjects without familial sinistrality, there was no statistically significant difference between the evoked potentials from the right and left sides. In the subjects with familial sinistrality, the mean amplitude of the N1 wave from the right cerebral cortex was found to be significantly larger than that from the left cerebral cortex. There was an inverse relationship between the lateralization quotient (LQ) for the N1 wave and left-hand preference. The amplitudes of the P1, N1, and P2 waves from the right cerebral cortex were positively linearly correlated with left-hand preference. There was an inverse relationship between LQ for the P1 and N1 waves and the right-hand skill. The left-hand skill was not correlated with LQ for the evoked potential. The LQs for the P1 and N1 waves were negatively linearly correlated with the difference between the right and left hand skills (right minus left peg moving times). The amplitudes of the P1 and N1 waves from the left cerebral cortex were found to be inversely related to the right hand skill. There was no relationship between the evoked potential amplitudes from the right cerebral cortex and left hand skill in the total sample. It was concluded that the stronger sensory feedback for the somatomotor foot area within the right cerebral cortex would contribute to left-footedness in left-handers; the asymmetric organization of the somatosensory potentials evoked by stimulation of the right and left PTNs correlates with hand preference and skill, but in an unexpected manner.     

Electrophysiologic correlates of visuo-spatial attention shift

We investigated neurophysiologic correlates of shifting visual attention across the visual field. Event-related potentials (ERPs) were recorded in 12 normal subjects during a visual discrimination task in which target stimuli were presented at a predictable or unpredictable location in the eccentric visual field. Subjects were obliged to shift their attention from the expected site to the unpredictable site immediately after the presentation of shifted stimuli in order to detect the change of stimulus attributes. Shifted stimuli modulated the NI component (130–200 msec), producing a larger amplitude at the posterior temporal site contralateral to the stimulus field and a smaller amplitude over the ipsilateral hemisphere. Furthermore, shifted stimuli uniquely evoked a positive ERP component with a latency of 200–300 msec, which distributed broadly over the skull maximally at the frontal and central electrode sites. Both the negative and positive components changed in amplitude as a function of shift distance and direction. These results suggest that modulations of the negative and positive deflections reflect the shift of covert visuo-spatial attention and that right hemispheric dominance does not exist at least in the early stage of shifting spatial attention.     

Rapid memory stabilization by transient theta coherence in the human medial temporal lobe

Presenting stimuli again after presentation of intervening stimuli improves their retention, an effect known as the spacing effect. However, using event‐related potentials (ERPs), we had observed that immediate, in comparison to spaced, repetition of pictures induced a positive frontal potential at 200–300 ms. This potential appeared to emanate from the left medial temporal lobe (MTL), a structure critical for memory consolidation. In this study, we tested the behavioral relevance of this signal and explored functional connectivity changes during picture repetition. We obtained high‐density electroencephalographic recordings from 14 healthy subjects performing a continuous recognition task where pictures were either repeated immediately or after 9 intervening items. Conventional ERP analysis replicated the positive frontal potential emanating from the left MTL at 250–350 ms in response to immediately repeated stimuli. Connectivity analysis showed that this ERP was associated with increased coherence in the MTL region—left more that right—in the theta‐band (3.5–7 Hz) 200–400 ms following immediate, but not spaced, repetition. This increase was stronger in subjects who better recognized immediately repeated stimuli after 30 min. These findings indicate that transient theta‐band synchronization between the MTL and the rest of the brain at 200–400 ms reflects a memory stabilizing signal. © 2015 Wiley Periodicals, Inc.     

Electrophysiological aspects of sensory conduction velocity in healthy adults. 2. Ratio between the amplitude of sensory evoked potentials at the wrist on stimulating different fingers in both hands.

The normal ratio between the amplitude of the sensory evoked potential (SEP) at the wrist on stimulating digits 1, 2, 3, and 5 was determined in 44 healthy adult subjects. The first digit had the larger amplitude, and the fifth digit the smallest SEP. The amplitude expresses the density of sensory innervation in each finger. The ratio between the amplitude of different fingers varied according to the age of the subject. The amplitude of the SEP from a digit innervated by the median nerve decreased in the elderly more than the SEP amplitude of the digit innervated by the ulnar nerve, probably because of a chronic compression in the carpal tunnel. The changes in the normal amplitude ratio can be applied to the topographic diagnosis of radicular and brachial plexus lesions if a fixed segmental sensory innervation of the hand is accepted. In 44 right handed subjects the amplitude of the sensory evoked potentials at the wrist was significantly larger in the left hand. This asymmetry of sensory innervation between hands could be physiological, and suggests a greater density of sensory innervation in the left hand of right handed subjects.     

Topographic evoked potentials during backward masking in schizophrenics, patient controls and normal controls

1. 1. A backward masking task with simultaneous measurement of topographically mapped evoked potentials was performed by normal, schizophrenic, and patient control subjects.

2. 2. Behavioral results replicated previous studies demonstrating schizophrenic deficit and to a lesser extent patient control deficit in this task.

3. 3. Two competing theories of (A) defects in “gating” mechanisms or (B) failure in early stimulus “registration” processes were tested.

4. 4. Topographical evoked response maps Indicated a significant absence of a negative going wave in the 70–100 msec epoch in the schizophrenic group relative to both control groups.

5. 5. As the 70–100 msec negativitity attenuation occurred during target presentation, and well before mask onset, it was concluded that schizophrenic deficit in this task consists of a failure in Initial stimulus “registration” processes within the time allowed for stimulus availability.

6. 6. Such defective mechanisms may be significant in the pathogenesis of schizophrenia.

Imitation of para-phonological detail following left hemisphere lesions

Imitation in speech refers to the unintentional transfer of phonologically irrelevant acoustic-phonetic information of auditory input into speech motor output. Evidence for such imitation effects has been explained within the framework of episodic theories. However, it is largely unclear, which neural structures mediate speech imitation and how imitation is related with verbal repetition. Two experiments were conducted, a standard repetition task, and a transformation task requiring phonetic manipulation of the presented auditory nonword stimuli. Nonword materials varied sub-phonemically in word stress (pitch elevation magnitude; PEM) and in a parameter related to speaking style, i.e., the explicitness of final schwa-syllables (SSE). We examined speech imitation in 10 healthy participants, 10 patients with phonological impairments after left hemisphere lesions, and 11 patients with right hemisphere lesions. In repetition, significant imitation of SSE and PEM was observed in all groups of participants. In transformation, imitation occurred in healthy participants and in the patients with right hemisphere lesions, whereas no imitation was observed in the patient group with left hemisphere lesions. Voxel-based lesion-symptom mapping revealed that different areas within the left temporal plane influenced the degree of imitation of phonetic and prosodic detail in repetition.     

Potentielse´voque´s visuels et somesthe´siqu es pendant le sommeil de l'homme

The authors studied the visual and somatosensory responses of 20 healthy adult subjects during the different phases of sleep and during the cloudy period which followed their awakening.

The evoked somatosensory responses were the most difficult to investigate; the subjects tended to wake up or enjoyed light sleep only during these studies. Nevertheless, it was possible to establish a great increase in the amplitude (which may be doubled) and the latency of the initial, positive wave during the first, second, third and fourth stages (classification by Dement and Kleitman)

During the 1-REM stage, the responses tended to take on a morphology comparable to that of wakefulness. The most remarkable modifications concerned the evoked visual responses. During the course of phases I–IV, one could observe a progressive and clear simplification of the responses. In all the subjects, whatever the differences existing in the state of wakefulness, the responses became superimposed and homogeneous: triphasic — positive, negative, positive. The homogeneity was absolute on the vertex; however, another type of response could be observed in the ‘specific regions’: biphasic — positive, negative.

During the 1-REM stage, the visual evoked responses took on the same morphology as during wakefulness with several very slight differences.

During the ‘cloudy period’ which followed the awakening, the responses on the vertex were different from those in the inion or in the occipital region. In these ‘specific regions’ the evoked response reached only very gradually the form and amplitude that the responses had during wakefulness; contrariwise, on the vertex the response took on its awakening morphology almost immediately.