Intracerebral interactions caused by bilateral median nerve stimulation in man: a magnetoencephalographic study

Cortical integration of bilateral nociceptive signals: when more is less

Integration of nociceptive information is essential to produce adapted responses, to promote body integrity and survival. However, how the brain integrates nociceptive inputs from different body areas remains unknown. The aim of this study was to examine the cortical integration of bilateral nociceptive inputs evoked by laser heat stimuli. Sixteen healthy volunteers (8 F, 8 M; age: 25.5 ± 4.3) were recruited to participate in one session during which painful laser stimuli were applied to their hands with 2 Nd:YAP laser systems. Electroencephalographic activity was recorded to measure laser-evoked potentials and event-related spectral perturbations. Twenty nociceptive stimuli were applied in each of the 4 counterbalanced conditions: (1) right hand, (2) left hand, and both hands with (3) attention to the right or (4) attention to the left. Compared with unilateral conditions, N2 and P2 peak amplitude as well as gamma oscillation power were decreased in bilateral conditions (P < 0.05), but these effects were not affected by the direction of attention (P > 0.1). By contrast, pain was not significantly different in any condition (P > 0.05). These findings show that although more nociceptive inputs reach the brain with multiple nociceptive stimuli, their sensory representation is decreased while pain perception remains unchanged. These interactions between cerebral processing of nociceptive information from different body regions could support coordinated behavioral responses when pain origins from multiple sources.

A multi-signature brain-computer interface: use of transient and steady-state responses

OBJECTIVE

The aim of this paper was to increase the information transfer in brain-computer interfaces (BCI). Therefore, a multi-signature BCI was developed and investigated. Stimuli were designed to simultaneously evoke transient somatosensory event-related potentials (ERPs) and steady-state somatosensory potentials (SSSEPs) and the ERPs and SSSEPs in isolation.

APPROACH

Twelve subjects participated in two sessions. In the first session, the single and combined stimulation conditions were compared on these somatosensory responses and on the classification performance. In the second session the on-line performance with the combined stimulation was evaluated while subjects received feedback. Furthermore, in both sessions, the performance based on ERP and SSSEP features was compared.

MAIN RESULTS

No difference was found in the ERPs and SSSEPs between stimulation conditions. The combination of ERP and SSSEP features did not perform better than with ERP features only. In both sessions, the classification performances based on ERP and combined features were higher than the classification based on SSSEP features.

SIGNIFICANCE

Although the multi-signature BCI did not increase performance, it also did not negatively impact it. Therefore, such stimuli could be used and the best performing feature set could then be chosen individually.

Non-transcallosal ipsilateral area 3b responses to median nerve stimulus

We report two patients with left hemisphere lesions who had no normal left hemispheric responses to right median nerve stimulus on magnetoencephalography but displayed right area 3b responses. One patient had suffered a severe left hemispheric contusion and the other left hemispheric infarction. Equivalent current dipoles of these ipsilateral responses were detected on the central sulcus adjacent to the location of the N20m response to left median nerve stimulus. The somatosensory afferent pathway from the hand may extend directly to the ipsilateral area 3b without following the transcallosal pathway in at least part of the population.

Characteristics of sensori-motor interaction in the primary and secondary somatosensory cortices in humans: a magnetoencephalography study

We studied sensori-motor interaction in the primary (SI) and secondary somatosensory cortex (SII) using magnetoencephalography. Since SII in both hemispheres was activated following unilateral stimulation, we analyzed SIIc (contralateral to stimulation) as well as SIIi (ipsilateral to stimulation). Four tasks were performed in human subjects in which a voluntary thumb movement of the left or right hand was combined with electrical stimulation applied to the index finger of the left or right hand: L(M)-L(S) (movement of the left thumb triggered stimulation to the left finger), L(M)-R(S) (movement of the left thumb triggered electrical stimulation to the right finger), R(M)-R(S) (movement of the right thumb triggered electrical stimulation to the right finger), and R(M)-L(S) (movement of the right thumb triggered electrical stimulation to the left finger). Stimulation to the index finger only (S condition) was also recorded. In SI, the amplitude of N20m and P35m was significantly attenuated in the R(M)-R(S) and L(M)-L(S) tasks compared with the S condition, but that for other tasks showed no change, corresponding to a conventional gating phenomenon. In SII, the R(M)-L(S) task significantly enhanced the amplitude of SIIc but reduced that of SIIi compared with the S condition. The L(M)-L(S) and R(M)-R(S) tasks caused a significant enhancement only in SIIi. The L(M)-R(S) task enhanced the amplitude only in SIIc. The laterality index showed that SII modulation with voluntary movement was more dominant in the hemisphere ipsilateral to movement but was not affected by the side of stimulation. These results provided the characteristics of activities in somatosensory cortices, a simple inhibition in SI but complicated changes in SII depending on the side of movement and stimulation, which may indicate the higher cognitive processing in SII.

Lateralization of brain activity during lower limb joints movement. An fMRI study

Studies of unilateral finger movement in right-handed subjects have shown asymmetrical patterns of activation in primary motor cortex and subcortical regions. In order to investigate the existence of an analogous pattern during lower limb joints movements, functional magnetic resonance imaging (fMRI) was used. Eighteen healthy, right leg dominant volunteers participated in a motor block design study, performing unilateral right and left repetitive knee, ankle and toes flexion/extension movements. Aiming to relate lower limb joints activation to the well-described patterns of finger movement, serial finger-to-thumb opposition was also assessed. All movements were auditory paced at 72 beats/min (1.2 Hz). Brain activation during movement of the nondominant joints was more bilateral than during the same movement performed with the dominant joints. Finger movement had a stronger lateralized pattern of activation in comparison with lower limb joints, implying a different functional specialization. Differences were also evident between the joints of the lower limb. Ankle and toes movements elicited the same extend of MR signal change in the majority of the examined brain regions, whereas knee joint movement was associated with a different pattern. Finally, lateralization index in primary sensorimotor cortex and basal ganglia was significantly affected by the main effect of dominance, whereas the lateralization index in cerebellum was significantly affected by the joint main effect, demonstrating a lateralization index increase from proximal to distal joints.

Response of SI cortex to ipsilateral, contralateral and bilateral flutter stimulation in the cat

Background

While SII cortex is considered to be the first cortical stage of the pathway that integrates tactile information arising from both sides of the body, SI cortex is generally not considered as a region in which neuronal response is modulated by simultaneous stimulation of bilateral (and mirror-image) skin sites.

Results

Optical intrinsic signal imaging was used to evaluate the response of SI and SII in the same hemisphere to 25 Hz sinusoidal vertical skin displacement stimulation ("skin flutter") applied contralaterally, ipsilaterally, and bilaterally (simultaneously) to the central pads of the forepaws. A localized increase in absorbance in both SI and SII occurred in response to both contralateral and bilateral flutter stimulation. Ipsilateral flutter stimulation evoked a localized increase in absorbance in SII, but little or no change in SI absorbance. In the forepaw representational region of SI, however, bilateral stimulation of the central pads evoked a response substantially smaller (approximately 30–35% smaller) than the response to flutter stimulation of the contralateral central pad.

Conclusion

The finding that the response of SI cortex to bilateral central pad flutter stimulation is substantially smaller than the response evoked by a contralateral flutter stimulus, together with the recently published observation that a region located posteriorly in SII responds with a substantially larger response to a bilateral flutter stimulus than the response evoked from the contralateral central pad, lead us to propose that the SI activity evoked by contralateral skin stimulation is suppressed/inhibited (via corticocortical connections between SII and SI in the same hemisphere) by the activity a simultaneous ipsilateral skin stimulus evokes in posterior SII.

Ipsilateral representation of oral structures in human anterior parietal somatosensory cortex and integration of inputs across the midline

Anterior parietal somatosensory areas 3a, 3b, 1, and 2 generally contain cells with receptive fields that are on the contralateral body. However, inputs from midline structures such as the mouth must be uniquely integrated across the midline. This hypothesis is supported by studies of these fields from nonhuman primates that demonstrate ipsilateral representations of oral structures. We used magnetoencephalography (MEG) to examine the cortical representations of the lips and tongue in humans and to examine the time course of interaction of bilateral inputs from these structures. Ipsilateral activation was observed in response to tactile stimulation of the upper lip in 69% of cases, the lower lip in 85% of cases, and the tongue in 88% of cases. In the contralateral hemisphere, the map of oral structures tended to be in agreement with that from nonhuman primates, although variation was large and source locations were not statistically significantly different from each other. There were no differences in latency of activation for ipsi-vs. contralateral responses (about 30 msec), and cortical sources from ipsi-and contralateral stimulation tended to be located together. Differential activation for bilateral vs. unilateral stimulation occurred later than activation in S1, around 110 msec, and was localized to the upper bank of the Sylvian sulcus. Our findings indicate that, unlike nonhuman primates, humans have an ipsilateral representation of the lips in 3b/1, possibly related to the precise manipulation necessary for the articulation of speech. The distinct pattern of differential activation for uni-vs. bilateral stimulation suggests a unique neural mechanism of integration across the midline for inputs from the mouth.

Hand posture modulates neuronal interaction in the primary somatosensory cortex of humans

OBJECTIVE

To investigate the effects of hand posture on the modulation of neuronal interactions in the cortical finger regions of the human somatosensory cortex.

METHODS

Neuronal magnetic fields, evoked by electrical stimuli to the thumb and/or to the index finger of the right hand, were recorded in different hand postures ('OPEN': opened hand and 'CLOSE': both fingers in opposite position to pick up something) by using a whole head type magnetoencephalography. The equivalent current dipole (ECD) for components in the primary (SI) and secondary somatosensory cortices (SII) was calculated. The interaction ratio (IR) was calculated as a ratio of the vector sum of ECD moments evoked by respective stimulation of each finger to the ECD moment evoked by simultaneous stimulation of both fingers.

RESULTS

The mean IR of N20m was significantly larger in CLOSE than in OPEN (p=0.033, ANOVA). On the contrary, the IR of P40m was larger in OPEN than in CLOSE (p=0.042). The IR of SII components was not significantly different between the different hand postures (p=0.35).

CONCLUSIONS

Neuronal interaction between the thumb and index finger in the human SI is modulated by hand posture. Provided that forming hand posture is related to receiving sensory input, the interaction modulation may play a role in the facilitation of somatosensory processing.

SIGNIFICANCE

Our results suggest experimental evidence for the immediate modulation of neuronal activity in the somatosensory area.

Left-hemisphere-dominant SII activation after bilateral median nerve stimulation

We used bilateral median nerve stimuli to find out possible hemispheric dominance in the activation of the second somatosensory cortex, SII. Somatosensory evoked fields (SEFs) were recorded from 14 healthy adults (7 right-handed, 7 left-handed) with a 306-channel neuromagnetometer. Electrical stimuli were applied once every 3 s simultaneously either to the left and right median nerves at the wrists or to the palmar skin of both thumbs. Sources of SEFs were modeled with four current dipoles, located in the SI and SII cortices of both hemispheres. The SI activation strengths did not differ between the hemispheres, whereas the SII responses were significantly stronger in the left than in the right hemisphere. In right-handers, the left/right SII ratios were 1.9 and 1.8 for wrist and thumb stimuli, respectively. The corresponding values were 1.5 and 1.7 in left-handers. The results indicate handedness-independent functional specialization of the human SII cortices.

Timing and connectivity in the human somatosensory cortex from single trial mass electrical activity

Parallel-distributed processing is ubiquitous in the brain but often ignored by experimental designs and methods of analysis, which presuppose sequential and stereotypical brain activations. We introduce here a methodology that can effectively deal with sequential and distributed activity. Regional brain activations elicited by electrical median nerve stimulation are identified in tomographic estimates extracted from single trial magnetoencephalographic signals. Habituation is identified in both primary somatosensory cortex (SI) and secondary somatosensory cortex (SII), often interrupted by resurgence of strong activations. Pattern analysis is used to identify single trials with homogeneous regional brain activations. Common activity patterns with well-defined connectivity are identified within each homogeneous group of single trials across the subjects studied. On the contralateral side one encounters distinct sets of single trials following identical stimuli. We observe in one set of trials sequential activation from SI to SII and insula with onset of SII at 60 msec, whereas in the other set simultaneous early co-activations of the same two areas.

A magnetoencephalographic study on development of the somatosensory cortex in infants

In order to examine the sensori-motor correlation in infants, we recorded the somatosensory evoked magnetic fields to tactile stimulation by using a 37-channel magnetoencephalograph. Twelve healthy infants were examined at palmar grasp stage and pincers grasp stage. Air-tapping stimulation of the right thumb was performed. Three distinct components (W1-3) emerged, W3, with a latency of approximately 100 ms, being the most prominent. As infants grew up, the correlation coefficient and the amplitude of the equivalent current dipole of W3 for the thumb increased. These developmental changes may be attributable to increases in the stability and reproducibility of the cortex in response to somesthetic inputs. Moreover, this change along with motor development supports the presence of a sensori-motor correlation in infants.

Functional overlap of finger representations in human SI and SII cortices

We aimed to find out to what extent functional representations of different fingers of the two hands overlap at the human primary and secondary somatosensory cortices SI and SII. Somatosensory evoked fields (SEFs) were recorded with a 306-channel neuromagnetometer from 8 subjects. Tactile stimuli, produced by diaphragms driven by compressed air, were delivered to the fingertips in three different conditions. First, the right index finger was stimulated once every 2 s. Then two other stimuli were interspersed, in different sessions, to right- or left-hand fingers (thumb, middle finger, or ring finger) between the successive right index finger stimuli. Strengths of the responses to right index finger stimuli were evaluated in each condition. Responses to right index finger stimuli were modeled by three current dipoles, located at the contralateral SI and the SII cortices of both hemispheres. The earliest SI responses, peaking around 65 ms, were suppressed by 18% (P < 0.05) when the intervening stimuli were presented to the same hand; intervening stimuli to the other hand had no effect. The SII responses were bilaterally suppressed by intervening stimuli presented to either hand: in the left SII, the suppression was 39 and 42% (P < 0.01) and in the right SII 67 and 72% (P < 0.001) during left- and right-sided intervening stimuli, respectively. Left- and right-sided intervening stimuli affected similarly the SII responses and had no effect on the response latencies. The results indicate a strong and symmetric overlap of finger representations for both hands in the human SII cortices, and a weaker functional overlap for fingers of the same hand in the SI cortex.

Evidence for interhemispheric processing of inputs from the hands in human S2 and PV

In the present investigation, we identified cortical areas involved in the integration of bimanual inputs in human somatosensory cortex. Using functional magnetic resonance imaging (fMRI) and magnetoencephalography (MEG), we compared the responses to unilateral versus bilateral stimulation in anterior parietal cortex and areas in the Sylvian fissure of the contralateral hemisphere. The extent of fMRI activation on the upper bank of the Sylvian fissure, in the second somatosensory (S2) and the parietal ventral (PV) areas, was significantly larger for bilateral stimulation than for unilateral stimulation. Using MEG, we were able to describe the latency of response in S1 and S2/PV to unilateral and bilateral stimulation. The MEG response had three components under both stimulus conditions. An early peak in S1 at 40 ms, a middle peak in S2/PV at 80-160 ms, and three late peaks in S2/PV at 250-420 ms. There was an increase in magnetic field strength in S2/PV to bilateral stimulation at 300-400 ms post stimulus. The fMRI results indicate that, as in monkeys, S2/PV receives inputs from both the contralateral and ipsilateral hand. The MEG data suggest that information is processed serially from S1 to S2. The very late response in S2/PV indicates that extensive intrahemispheric processing occurs before information is transferred to the opposite hemisphere. The neural substrate for the increased activation and field strength at long latencies during bilateral stimulation can be accounted for in three ways. Under bilateral stimulus conditions, more neurons may be active, neuronal firing rate may increase, and/or neural activity may be more synchronous.

The somatosensory evoked magnetic fields

Averaged magnetoencephalography (MEG) following somatosensory stimulation, somatosensory evoked magnetic field(s) (SEF), in humans are reviewed. The equivalent current dipole(s) (ECD) of the primary and the following middle-latency components of SEF following electrical stimulation within 80-100 ms are estimated in area 3b of the primary somatosensory cortex (SI), the posterior bank of the central sulcus, in the hemisphere contralateral to the stimulated site. Their sites are generally compatible with the homunculus which was reported by Penfield using direct cortical stimulation during surgery. SEF to passive finger movement is generated in area 3a or 2 of SI, unlike with electrical stimulation. Long-latency components with peaks of approximately 80-120 ms are recorded in the bilateral hemispheres and their ECD are estimated in the secondary somatosensory cortex (SII) in the bilateral hemispheres. We also summarized (1) the gating effects on SEF by interference tactile stimulation or movement applied to the stimulus site, (2) clinical applications of SEF in the fields of neurosurgery and neurology and (3) cortical plasticity (reorganization) of the SI. SEF specific to painful stimulation is also recorded following painful stimulation by CO(2) laser beam. Pain-specific components are recorded over 150 ms after the stimulus and their ECD are estimated in the bilateral SII and the limbic system. We introduced a newly-developed multi (12)-channel gradiometer system with the smallest and highest quality superconducting quantum interference device (micro-SQUID) available to non-invasively detect the magnetic fields of a human peripheral nerve. Clear nerve action fields (NAFs) were consistently recorded from all subjects.

Dipolar source modeling of somatosensory evoked potentials to painful and nonpainful median nerve stimulation

Dipolar source modeling might help in clarifying whether somatosensory evoked potentials (SEPs) after electrical stimulation at painful intensity contain any information related to the nociceptive processing. SEPs were recorded after left median nerve stimulation at three different intensities: intense but nonpainful (intensity 2); slightly painful (pain threshold; intensity 4); and moderately painful (intensity 6). Scalp SEPs at intensities 2, 4, and 6 were fitted by a five-dipole model. When the strength modifications of the source activities up to 40 ms were examined across the different stimulus intensities, no significant difference was found. In the later epoch (40-200 ms), a posterior parietal dipole and two bilateral sources probably located in the second somatosensory (SII) areas increased significantly their dipole moments when the stimulus was increased from 2 to 4 and became painful. Since no difference was found when the stimulus intensity was increased from 4 to 6, the observed increase of the dipolar strengths is probably related to a variation of the stimulus quality (nonpainful vs. painful), rather than of the stimulus intensity per se. Our findings lead us to conclude that a large convergence of nociceptive and non-nociceptive afferents probably occurs bilaterally in the SII areas.

Activation of the somatosensory cortex during Abeta-fiber mediated hyperalgesia. A MSI study

OBJECTIVE

To investigate the neural activation in the primary somatosensory cortex (SI) that is induced by capsaicin-evoked secondary Abeta-fiber-mediated hyperalgesia with magnetic source imaging (MSI) in healthy humans.

BACKGROUND

Dynamic mechanical hyperalgesia, i.e. pain to innocuous light touching, is a symptom of painful neuropathies. Animal experiments suggest that alterations in central pain processing occur so that tactile stimuli conveyed in Abeta low threshold mechanoreceptive afferents become capable of activating central pain signalling neurons. A similar state of central sensitization can be experimentally produced with capsaicin.

METHODS

In six individuals the somatosensory evoked magnetic fields (SEFs) induced by non-painful electrical stimulation of Abeta-afferents at the forearm skin were recorded. Capsaicin was injected adjacent to the stimulation site to induce secondary dynamic Abeta-hyperalgesia. Thereafter, the SEFs induced by the identical electrical stimulus applied within the secondary hyperalgesic skin were analyzed. The electrical stimulus was subsequently perceived as painful without changing the stimulus intensity and location. Latencies, anatomical source location and amplitudes of SEFs during both conditions were compared.

RESULTS

Non-painful electrical stimulation of Abeta-afferents induced SEFs in SI at latencies between 20 and 150 ms. Stimulation of Abeta-afferents within the capsaicin-induced secondary hyperalgesic skin induced SEFs at identical latencies and locations as compared with the stimulation of Abeta-afferents within normal skin. The amplitudes, i.e., the magnetic dipole strengths of the SEFs were higher during Abeta-hyperalgesia.

CONCLUSIONS

Acute application of capsaicin produces an increase in the excitability of central neurons, e.g., in SI. This might be due to sensitization of central neurons so that normally innocuous stimuli activate pain signalling neurons or cortical neurons might increase their receptive fields.

Differential interaction of somatosensory inputs in the human primary sensory cortex: a magnetoencephalographic study

OBJECTIVE

Somatosensory evoked magnetic fields (SEFs) were recorded to investigate the interaction of the somatosensory inputs using the modality of electrical finger stimulation in 6 normal subjects.

METHODS

Electrical stimuli were given to the index (II), middle (III) or little (V) fingers individually, and also to pairs of either the II and III simultaneously, or the II and V simultaneously. The interaction ratio (IR) was calculated as the ratio of the SEF amplitude by simultaneous two-finger stimulation to the arithmetically summed SEF amplitudes of two individual-finger stimulations.

RESULTS

SEFs showed 3 major components: N22m, P30m and P60m. The N22m and P60m revealed a clear somatotopic organization in the primary sensory cortex (S1) in the sequence of II, III and V, while the P30m showed a cluster with medial location compared with N22m and P60m in S1. The N22m had a significantly greater IR in II and III stimulation compared to that in II and V stimulation. The P60m also showed a similar trend in the IR but was greater than that of N22m. In contrast, the IR in P30m showed no such tendency.

CONCLUSION

The interaction of S1 was most influenced when adjacent receptive fields were activated in the modality of electrical finger stimulation. Our results were consistent with the concept that the Brodmann's areas in S1 which produce the 3 components of the SEFs have different functional organization.

Magnetoencephalography in the study of human somatosensory cortical processing

Magnetoencephalography (MEG) is a totally non-invasive research method which provides information about cortical dynamics on a millisecond time-scale. Whole-scalp magnetic field patterns following stimulation of different peripheral nerves indicate activation of an extensive cortical network. At the SI cortex, the responses reflect mainly the activity of area 3b, with clearly somatotopical representations of different body parts. The SII cortex is activated bilaterally and it also receives, besides tactile input, nociceptive afference. Somatically evoked MEG signals may also be detected from the posterior parietal cortex, central mesial cortex and the frontal lobe. The serial versus parallel processing in the cortical somatosensory network is still under debate.

Hierarchical somatosensory processing

Recent studies of the postcentral and additional somatosensory cortices support a hierarchical scheme for information processing. In the postcentral gyrus, the complexity of receptive field properties increases with caudal progression from area 1. It has been reported that the anterior bank of the intraparietal sulcus, the caudalmost part of the postcentral gyrus, is responsible for the systematic integration of bilateral body parts, as well as of somatic and visual information.

Magnetoencephalographic study of intracerebral interactions caused by bilateral posterior tibial nerve stimulation in man

We studied somatosensory evoked magnetic fields (SEFs) following stimulation of bilateral posterior tibial nerves ('bilateral' waveform) in normal subjects to determine the inter- and intra-hemispheric interference effects caused by activation of sensory areas in bilateral hemispheres. Activated areas in the primary and second sensory cortices (SI and SII) in each hemisphere following bilateral stimulation were clearly identified by estimation of the double best-fitted equivalent current dipoles (ECD) using the spherical head model, and the large inter-individual differences were identified. SEFs following the right posterior tibial nerve stimulation and those following the left stimulation were summated ('summated' waveform). The 'difference' waveform was induced by a subtraction of 'bilateral' waveforms from the 'summated' waveform. Short-latency deflections showed no consistent changes between the 'summated' and 'bilateral' waveforms, but the long-latency deflection, the N100m-P100m, in the 'bilateral' waveform was significantly (P < 0.02) reduced in amplitude as compared with the 'summated' waveform. The differences were clearly identified in the 'difference' waveform, in which the main deflections, U100m-D100m, were found. The ECDs of the short-latency deflections were located in SI contralateral to the stimulated nerve, but the ECDs of the N100m-P100m were located in bilateral SII which are considered to receive ascending signals from the body bilaterally. Therefore, some inhibitory interactions might take place in SII by receiving inputs from the body bilaterally.

Effects of sleep on somatosensory evoked responses in human: a magnetoencephalographic study

We studied the effects of sleep on somatosensory evoked magnetic fields (SEFs) following median nerve stimulation in normal subjects, to investigate the changes of functional processing of sensory perception in the primary and second sensory cortices (SI and SII). The early components, 1M, 2M and 3M, which were generated in SI contralateral to the stimulated nerve, showed no significant change of latency or amplitude in stage 1 or 2 as compared with those in the awake state. The long-latency response, 4M whose latency was about 100 ms, was significantly enhanced in stage 2. The 4M was considered to be generated in SI and SII in the awake state, but the enhanced 4M in stage 2 was restricted in SI. The 4M(I) generated in SII of the hemisphere ipsilateral to the stimulated nerve, corresponding to 4M in the contralateral hemisphere, was absent during sleep. These findings were probably due to the difference of activities between SI and SII during sleep, that is, an increase of sensitivity to somatosensory stimulation in SI but a decrease or disappearance in SII.