Pakhomov Sv

Lateralized Automatic Auditory Processing of Phonetic Versus Musical Information: A PET Study

Previous positron emission tomography (PET) and functional magnetic resonance imaging (fMRI) studies show that during attentive listening, processing of phonetic information is associated with higher activity in the left auditory cortex than in the right auditory cortex while the opposite is true for musical information. The present PET study determined whether automatically activated neural mechanisms for phonetic and musical information are lateralized. To this end, subjects engaged in a visual word classification task were presented with phonetic sound sequences consisting of frequent (P = 0.8) and infrequent (P = 0.2) phonemes and with musical sound sequences consisting of frequent (P = 0.8) and infrequent (P = 0.2) chords. The phonemes and chords were matched in spectral complexity as well as in the magnitude of frequency difference between the frequent and infrequent sounds (/e/ vs. /o/; A major vs. A minor). In addition, control sequences, consisting of either frequent (/e/; A major) or infrequent sounds (/o/; A minor) were employed in separate blocks. When sound sequences consisted of intermixed frequent and infrequent sounds, automatic phonetic processing was lateralized to the left hemisphere and musical to the right hemisphere. This lateralization, however, did not occur in control blocks with one type of sound (frequent or infrequent). The data thus indicate that automatic activation of lateralized neuronal circuits requires sound comparison based on short‐term sound representations. Hum. Brain Mapping 10:74–79, 2000.

Comparison of brain activation after sustained non-fatiguing and fatiguing muscle contraction: a positron emission tomography study

The concept of fatigue refers to a class of acute effects that can impair motor performance, and not to a single mechanism. A great deal is known about the peripheral mechanisms underlying the process of fatigue, but our knowledge of the roles of the central structures in that process is still very limited. During fatigue, it has been shown that peripheral apparatus is capable of generating adequate force while central structures become insufficient/sub-optimal in driving them. This is known as central fatigue, and it can vary between muscles and different tasks. Fatigue induced by submaximal isometric contraction may have a greater central component than fatigue induced by prolonged maximal efforts. We studied the changes in regional cerebral blood flow (rCBF) of brain structures after sustained isometric muscle contractions of different submaximal force levels and of different durations, and compared them with the conditions observed when the sustained muscle contraction becomes fatiguing. Changes in cortical activity, as indicated by changes in rCBF, were measured using positron emission tomography (PET). Twelve subjects were studied under four conditions: (1) rest condition; (2) contraction of the m. biceps brachii at 30% of MVC, sustained for 60 s; (3) contraction at 30% of MVC, sustained for 120 s, and; (4) contraction at 50% of MVC, sustained for 120 s. The level of rCBF in the activated cortical areas gradually increased with the level and duration of muscle contraction. The fatiguing condition was associated with predominantly contralateral activation of the primary motor (MI) and the primary and secondary somatosensory areas (SI and SII), the somatosensory association area (SAA), and the temporal areas AA and AI. The supplementary motor area (SMA) and the cingula were activated bilaterally. The results show increased cortical activation, confirming that increased effort aimed at maintaining force in muscle fatigue is associated with increased activation of cortical neurons. At the same time, the activation spread to several cortical areas and probably reflects changes in both excitatory and inhibitory cortical circuits. It is suggested that further studies aimed at controlling afferent input from the muscle during fatigue may allow a more precise examination of the roles of each particular region involved in the processing of muscle fatigue.

Hemispheric lateralization of cerebral blood-flow changes during selective listening to dichotically presented continuous speech.

Regional cerebral blood flow (rCBF) was measured with positron emission tomography (PET) while subjects were selectively listening to continuous speech delivered to one ear and ignoring concurrent speech delivered to the opposite ear, as well as concurrent text or letter strings running on a screen. rCBF patterns associated with selective listening either to the left-ear or right-ear speech message were compared with each other and with rCBF patterns in two visual-attention conditions in which the subjects ignored both speech messages and either read the text or discriminated the meaningless letter strings moving on the screen. Attention to either speech message was associated with enhanced activity in the superior temporal cortex of the language-dominant left hemisphere, as well as in the superior and middle temporal cortex of the right hemisphere suggesting enhanced processing of prosodic features in the attended speech. Moreover, enhanced activity during attention to either speech message was observed in the right parietal areas known to have an important role in directing spatial attention. Evidence was also found for attentional tuning of the left and right auditory cortices to select information from the contralateral auditory hemispace.

Brain processing of tonic muscle pain induced by infusion of hypertonic saline

Most of the previous studies on the effects of pain on Regional Cerebral Blood Flow (rCBF) had been done with brief cutaneous or intramuscular painful stimuli. The aim of the present study was to investigate the effect on rCBF of long lasting tonic experimental muscle pain. To this end we performed PET investigations of rCBF following tonic experimental low back pain induced by continuous intramuscular infusion of hypertonic (5%) saline (HS) with computer controlled infusion pump into the right erector spinae on L3 level in 19 healthy volunteers. Changes in rCBF were measured with the use of 15O labelled water during four conditions: Baseline (before start of infusion), Early Pain (4 min after start of infusion), Late Pain (20 min after start of infusion) and Post‐Pain (>15 min after stop of infusion) conditions.

Study of the Brain Organization of Creativity: III. Brain Activation Assessed by the Local Cerebral Blood Flow and EEG

In this article, a polymethodological approach was applied to the analysis of the brain organization of creative thinking. The electroencephalographic studies and the investigation of the local cerebral blood flow by means of positron-emission tomography in the same testing conditions substantially validate and supplement each other. The physiological indices of subjects were recorded during the composition of stories with the given words belonging to the same or different semantic fields. The reconstruction of correct grammatical forms in a presented text and memorizing of a set of words were used as control tasks. The fundamental importance of the processes taking place in both frontal lobes (Brodmanns areas (BA) 8–11 and 44–47) and the interhemispheric interaction was demonstrated.

Selective attention to human voice enhances brain activity bilaterally in the superior temporal sulcus.

Regional cerebral blood flow was measured with positron emission tomography (PET) in 10 healthy male volunteers. They heard two binaurally delivered concurrent stories, one spoken by a male voice and the other by a female voice. A third story was presented at the same time as a text running on a screen. The subjects were instructed to attend silently to one of the stories at a time. In an additional resting condition, no stories were delivered. PET data showed that in comparison with the reading condition, the brain activity in the speech-listening conditions was enhanced bilaterally in the anterior superior temporal sulcus including cortical areas that have been reported to be specifically sensitive to human voice. Previous studies on attention to non-linguistic sounds and visual objects, in turn, showed prefrontal activations that are presumably related to attentional control functions. However, comparisons of the present speech-listening and reading conditions with each other or with the resting condition indicated no prefrontal activity, except for an activation in the inferior frontal cortex that was presumably associated with semantic and syntactic processing of the attended story. Thus, speech listening, as well as reading, even in a distracting environment appears to depend less on the prefrontal control functions than do other types of attention-demanding tasks, probably because selective attention to speech and written text are over-learned actions rehearsed daily.

Study of the Brain Organization of Creative Thinking

This article is a continuation of a series of works on the brain organization of creative thinking. It was shown in earlier studies that, when solving creative tasks, subjects choose between two strategies (successive and insight), and the results of the study of the brain mechanisms of the successive strategy were described [1–3]. The results of positron-emission tomography (PET) study of the second (insight) strategy of solving creative tasks are presented in this communication.

Cerebral mechanisms of error detection during deceptive responses in the normal state and under the influence of alcohol

Event-related potentials (ERPs) were studied during deceptive and truthful responses of subjects that were in the normal state or under the influence of alcohol. The psychological task was designed in such a way that the subjects themselves decided whether or not they would tell a lie. Thirteen healthy volunteers participated in the study. An actual deceptive answer was characterized by a higher amplitude of the frontocentral ERP N190 component compared to the ERP accompanying a truthful answer. Alcohol consumption inverted the ratio between the amplitudes of this component in the cases of deceptive and truthful answers (with a higher amplitude in the latter case). The obtained result suggests that a deceptive action activates the so-called cerebral error detector. Under the influence of alcohol, the cerebral error detection system functioned abnormally, so that a deceptive action was not perceived as erroneous. This disturbance of automatic control may account for the lower amplitude of the late positive component of ERPs, which, in our opinion, reflects the process of making a decision on a deceptive response. This may explain why, e.g., alcohol consumption by a driver is hazardous: the activity is mainly controlled by conscious processes (the probability of making “the only right decision” in a critical situation is decreased, reactions become slow, etc.). Thus, the experimental model where the subject consumes a small amount of alcohol may be used for studying the altered functional mode of the cerebral error detector. Such studies seem promising in terms of searching for and developing methods for noninvasive modification of the error detector activity that could be used, e.g., in treatment for obsessions.

Stages of the cerebral mechanisms of deceptive responses

Cerebral mechanisms of perceiving and telling lies were studied by recording event-related potentials (ERPs) both after an actual deceptive response and during the time interval when the subject decided to tell a lie. Ten healthy volunteers participated in the study. The test consisted of their playing a game against a computer. The subjects could choose between deceptive and truthful answers so as to win the game. The subjects gave a deceptive answer intentionally, the structure of the test ensuring equal numbers of deceptive and truthful answers. The relaxation times in the cases of truthful and deceptive answers did not differ significantly from each other. The comparison of ERPs accompanying deceptive and truthful answers showed the existence of a negativity with a latent period of 90 ms in the regions of the right frontal, central, and right parietal derivations. This negativity indicated that the brain reacted to a deceptive answer even if this a priori “erroneous” act ensured reaching the goal and, in this sense, was subjectively relevant. In terms of the cerebral error detector mechanism, this phenomenon may be regarded as a special case of a general response of the brain to giving an incorrect (deceptive) answer, rather than a response to a lie per se. The interval of time when, presumably, the decision on a deceptive answer was being made was found to contain the late positive component P540, which is most likely to be involved in the preparation of the deceptive answer and the intention to tell a lie.

Mechanisms of Selective Attention during Competitive Discrimination of Visual and Auditory Verbal Information: Positron Emission Tomography and Cortical Evoked Potential Studies

The mechanisms of selective verbal attention were studied under conditions of simultaneous delivery of speech signals via the visual and auditory channels. The investigation was based on the comparison and synthesis of data obtained by two methods: positron emission tomography (PET) and brain evoked potentials (EPs). A new approach was developed: complementary tasks were constructed in such a way that, despite principal methodological problems, the same phenomenon could be investigated in one paradigm in EP and PET studies. The results obtained by the two methods are in rather good agreement with respect to topography: the secondary and tertiary areas, as well as the associative brain areas, are involved in attention concentration, that is, selection of verbal information occurs at the level of cognitive processes. The combination of two complementary methods, PET and EP, allowed the processes of processing of sensory information and brain mechanisms of selective attention to be investigated much more completely. The PET studies contributed to further understanding of brain mechanisms evidencing where processing occurs and the EP method provided insight into the mechanism of how this information is processed inside the corresponding cortical areas. The finding that the activation of primary areas of the visual cortex is accompanied by the inhibition of visual information deserves attention. This conclusion can be considered highly significant because of the concordance of the two independent methods. How to interpret it is not yet clear. It is possible that, in the case of primary importance of verbal information and priority of the visual channel for the repression from consciousness of artificially irrelevant information, a safety mechanism is activated: the amplified signal enters the brain cortex, where it is retained in the short-term “iconic” memory. This enables a reaction to this stimulus (if necessary), in the presence of any additional sign involving selective attention.