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• W4250069235 abstract "Full text Figures and data Side by side Abstract eLife digest Introduction Results Discussion Material and methods References Decision letter Author response Article and author information Metrics Abstract It is unclear whether the two hippocampal lobes convey similar or different activities and how they cooperate. Spatial discrimination of electric fields in anesthetized rats allowed us to compare the pathway-specific field potentials corresponding to the gamma-paced CA3 output (CA1 Schaffer potentials) and CA3 somatic inhibition within and between sides. Bilateral excitatory Schaffer gamma waves are generally larger and lead from the right hemisphere with only moderate covariation of amplitude, and drive CA1 pyramidal units more strongly than unilateral waves. CA3 waves lock to the ipsilateral Schaffer potentials, although bilateral coherence was weak. Notably, Schaffer activity may run laterally, as seen after the disruption of the connecting pathways. Thus, asymmetric operations promote the entrainment of CA3-autonomous gamma oscillators bilaterally, synchronizing lateralized gamma strings to converge optimally on CA1 targets. The findings support the view that interhippocampal connections integrate different aspects of information that flow through the left and right lobes. https://doi.org/10.7554/eLife.16658.001 eLife digest In humans and other backboned animals, the brain is divided into the left and right hemispheres, which are connected by several large bundles of nerve fibers. Thanks to these fiber tracts, sensory information from each side of the body can reach both sides of the brain. However, although many areas of the brain work with a counterpart on the opposite hemisphere to process this sensory information, they do not necessarily perform the same tasks, or perform them at the same time as their partner. The hippocampus is a brain region that helps to support navigation, to detect novelty, and to produce memories. In fact, our brains contain two hippocampi – one in each hemisphere. Previous studies of the hippocampus have tended to record from only one side of the brain. Benito, Martín-Vázquez, Makarova et al. now compare the activity of the left and right hippocampi, and consider how the two structures might work together. Recordings of the electrical activity of the hippocampi of anesthetized rats show that different groups of neurons fire in rhythmic sequence, forming waves called gamma waves. Successive waves have different amplitudes, and can be thought to form ‘strings’. The recordings made by Benito et al. show that the two hippocampi produce parallel strings of waves, although the waves that originate in the right hemisphere are generally larger than those that originate in the left. Right-hemisphere waves also tend to begin slightly earlier than their left-hemisphere counterparts. Further experiments revealed that disrupting the fiber tracts between the hemispheres uncouples the waves that no longer occur at the same time, and the strings of waves may remain constrained to one side of the brain. In healthy animals, however, the right-hand dominance acts as a master-slave device, and makes the waves from the two hemispheres pair up and merge in the neurons that receive them both. Thus the information running in both hippocampi can be integrated or compared before sending to the cortex for task execution or storage. Overall, the findings reported by Benito et al. suggest that different types of information flow through the left and right hemispheres, and that the brain integrates these two streams using asymmetric connections. The next challenge is to identify how the information in the two streams differs: whether each stream reflects different sensory stimuli, different features of a scene, or the difference between recalled and perceived information. https://doi.org/10.7554/eLife.16658.002 Introduction Lateralization of certain neural functions in vertebrates is thought to bear evolutionary advantages (Halpern et al., 2005). Earlier studies have mainly focused on finding anatomical correlates to behavioral asymmetries, but there has been little insight gained into the functional mechanisms underlying the differential routing and integration of activity in bilateral networks. For example, fMRI studies have shown bilateral or lateral activation of the same structures when subject performs different tasks (Smith and Goodale, 2015; Lee et al., 2016). The bilateral function in the hippocampus is largely unknown and it is unclear to what extent the two lobes convey similar or complementary information, and whether they do indeed work together. However, the existence of important bilateral connections between the same and different hippocampal subregions does suggest some degree of integration and cooperation. In rodents, hippocampal lateralization is observed during certain memory tasks (Klur et al., 2009; Shipton et al., 2014), in the expression of synaptic plasticity (Kohl et al., 2011), or following environmental enrichment (Shinohara et al., 2013). In the human, such lateralization was reported during sequence disambiguation (Kumaran and Maguire, 2006) and in cognitive navigation (Iaria et al., 2003; Iglói et al., 2015). Available data is however limited and it provides no mechanistic insights. Here we have used pathway-specific local field potentials (LFPs) (Herreras et al., 2015) in anesthetized rats to study the spontaneous transmission in the bilateral CA3→CA1 Schaffer segment during irregular non-theta EEG states, a pattern that in active animals is associated to sensory input during immobility and consummatory behaviors. The hippocampal CA3 region is an important hub for ascending and cortical pathways (Vinogradova, 2001), and its output is conveyed to numerous brain regions, directly or from the next station in the CA1 after bilateral integration (Swanson et al., 1981). The left and right CA3 are connected reciprocally through the ventral hippocampal commissure (VHC), and they also send excitatory inputs to the CA1 on both sides of the brain through an associational (Schaffer)-commissural system that converges on pyramidal cells (PCs, Figure 1A). Hence, this system represents an ideal model to explore the flow of activity and its integration in bilateral networks. In addition, numerous electrophysiological studies show that the CA3 region behaves as a powerful gamma oscillator with inhibitory and excitatory local network components (Traub et al., 1996; Fisahn et al., 1998; Bartos et al., 2002; Csicsvari et al., 2003; Hájos et al., 2004; Mann et al., 2005; Oren et al., 2006; Hájos and Paulsen, 2009; Pietersen et al., 2009; Gulyás et al., 2010; Mann and Mody, 2010; Kohus et al., 2016). Whether and how the left and right CA3 gamma oscillators are coupled and how this influences the bilateral activity and performance of the hippocampus have not been explored. Figure 1 with 1 supplement see all Download asset Open asset Experimental paradigm and clean out of the Schaffer and CA3som activities. (A) Functional characteristics of the bilateral CA3→CA1 segment: (1) an intrinsic gamma oscillator fueled by inhibition in each CA3 region produces gamma output from PCs; (2) The left and right CA3-PCs are interconnected through the ventral hippocampal commissure (VHC, maroon arrows), enabling the coupling of CA3 gamma oscillators; (3) The excitatory outputs of CA3-PCs from both sides converge in each CA1 (Schaffer and Commissural pathways). (B) Experimental setup. Two-shank linear arrays were located at homotopic sites of the dorsal left and right hippocampi. Recordings were acquired simultaneously and each group was analyzed separately by an Independent Component Analysis (ICA). (C) ICA of a sample epoch across the CA1 and CA3/DG layers. In raw LFPs (black traces), several bands of coherent voltage fluctuations are observed that indicate multiple activation in different synaptic territories (three are outlined by filled ovals spanning the CA1 and the Dentate subfields, while small maroon ovals mark activity in the st. pyramidale of the CA3). The ICA returns the spatially-coherent components and provides readout of the temporal dynamics free of a contribution by the others. A set of components or LFP-generators was obtained per shank, each with a characteristic spatial distribution or voltage weight (Vwt) that enabled matching between shanks. Details of the extraction are in Figure 1—figure supplement 1. Colored traces from top to bottom: Schaffer (cyan), CA3som (maroon), lacunosum-moleculare (green), and GCsom (purple). The amplitudes are normalized (0.37:0.25:0.84:1). In other figures voltage units are employed that were estimated for the sites with maximum power (triangles in Vwt plots). https://doi.org/10.7554/eLife.16658.003 We set out to compare the dynamic relationships of two network components that can be addressed on a cell-assembly basis using pathway-specific LFPs, the CA3 PC excitatory output reflected in CA1 Schaffer LFPs, and a somatic inhibitory input to the same population (CA3som). We also studied the impact of excitatory bilateral convergence on the output of neurons in the next station, the CA1, by comparing the waveform details of Schaffer gamma waves on both sides and cell firing of CA1 units. To extract the Schaffer and CA3som LFP activities from the field contributions added by other concurrent pathways, we applied a spatial discrimination method to multisite linear LFP recordings (Figure 1B) (Herreras et al., 2015). This approach provides unprecedented temporal precision and specification of the origin such that each spatially-isolated activity reflects the envelope of postsynaptic currents elicited by an afferent population on another (Makarova et al., 2011; Fernandez-Ruiz et al., 2012a; Martín-Vázquez et al., 2013; Schomburg et al., 2014; Herreras et al., 2015). Indeed, we previously reported that the Schaffer LFPs contain a regular succession of gamma waves (gamma strings) that reflect excitatory packages of extremely variable amplitude (Fernandez-Ruiz et al., 2012a, 2012b), these being elicited in CA1 PCs by the synchronous firing of CA3 PC assemblies at gamma intervals (Fisahn et al., 1998; Hájos and Paulsen, 2009; Takahashi et al., 2010; Fernandez-Ruiz et al., 2012a). The respective excitatory and inhibitory nature of Schaffer and CA3som gamma waves has also been established previously (Hájos et al., 2004; Benito et al., 2014). These studies indicate that Schaffer and CA3som gamma waves are generally larger and lead from the right lobe, while the CA3som component forms part of a local gamma oscillator that paces outgoing excitatory Schaffer packages. These form strings of gamma waves that may run unilaterally as seen upon VHC disconnection. In both sides, Schaffer waves may lead at different antero-posterior CA1 locations indistinctly, although they are all submitted to global bilateral asymmetric entrainment that optimizes bilateral convergence in the CA1. This inference is supported by the preferred firing of CA1 pyramidal cells during bilateral waves in contrast to the preferred unilateral driving of putative interneurons. Results The mean frequency of LFPs recorded in the stratum radiatum of CA1 was 45.2 ± 1.2 Hz (estimated from the autocorrelation function on 10 min epochs, n = 7 animals), which corresponds to the so-called low-gamma frequency band that characterizes the hippocampal segment under study (Csicsvari et al., 2003; Fernandez-Ruiz et al., 2012a, 2012b; Martín-Vázquez et al., 2013; Schomburg et al., 2014). Here we use the term gamma wave to refer to each pulse-like fluctuation of the LFP repeating at intervals of 20–25 ms, i.e. the wavelength of the oscillation, regardless of the duration of individual waves that differ for specific synaptic pathways (see below). Epochs containing layer-specific strings of gamma waves were observed in all hippocampal subregions, but they blend with activities at multiple frequencies and temporal patterns in a variable fashion (Figure 1C). Accordingly, the precise time course of individual waves cannot be reasonably assigned to a specific synaptic pathway. By using independent component analysis (ICA) (Bell and Sejnowski, 1995) to maximize spatially coherent activity, we isolated a small number of pathway-specific LFPs (colored traces) with characteristic spatial voltage weights (Vwt) that corresponded to a linear sample of the voltage shell produced by each synaptic pathway in the volume (Herreras et al., 2015). The populations of origin and the postsynaptic targets (pyramidal or granule cells) have been identified elsewhere (Bell and Sejnowski, 1995; Korovaichuk et al., 2010; Fernandez-Ruiz et al., 2012a; 2012b; Martín-Vázquez et al., 2013, 2015; Schomburg et al., 2014). We here studied the Schaffer-specific CA3→CA1 excitatory input that reflects assembly organization of CA3 output, and the somatic CA3 inhibitory input (Figure 1C, cyan and maroon traces, respectively). Details of the contributions cleaned of any influence of nearby sources in the stratum lacunosum-moleculare (s.l-m.) of the CA1, or the Dentate Gyrus (DG), respectively, are shown in Figure 1—figure supplement 1. Schaffer gamma activity is stronger and precedes in the right side The Schaffer activity contained strings of gamma waves, irregular fluctuations, and Sharp-Waves (SPW), each reflecting different regimes of organized firing in CA3 PCs (Benito et al., 2014). The occurrence and duration of gamma strings was unpredictable, ranging from a few waves to many seconds and they were no further characterized. To test the bilateral complementariness we first compared the time course of Schaffer activity as a whole (containing interspersed gamma strings and irregular fluctuations) in two pairs of left-right homotopic sites of the dorsal hippocampus (Figure 2A and Figure 2—figure supplement 1). Epochs with frequent SPWs were avoided or these were removed as they contribute disproportionately to the statistics. We found significant wide band coherence between pairs of sites that are 0.5 mm apart within antero-posterior (a-p) lamellar strips. This coherence is reduced and restricted to the gamma band in bilateral comparisons (Figure 2—figure supplement 2). The cross-correlation coefficient (CC) behaved similarly (La-Lp, 0.84 ± 0.03; Ra-La, 0.57 ± 0.04; F(1,12) = 26.9; p<0.001; mean of epochs lasting 85–167 s, n = 7). The mean τmax of CCs was similar for a-p sites (0.32 ± 0.2 ms) but shifted -0.82 ± 0.3 ms (F(1,12) = 8.5, p=0.01) for La-Ra comparisons, with the right side leading. Figure 2 with 3 supplements see all Download asset Open asset Functional asymmetry in the bilateral CA3-CA1 system. (A) Sample string of Schaffer-gamma obtained from four sites. Individual waves coincide regardless of their amplitude. Globally, Schaffer-gamma is larger on the right side. The scheme shows the location of recordings from a coronal view (Figure 2—figure supplement 1). (B–E) Representative experiment showing the features of individual waves compared pairwise within (La,Lp) and between hippocampi (La,Ra) (n = 6623 pairs of waves in 167 s). The blue and red dots belong to the pairs when L or R waves were longer, respectively. The population statistics and additional examples are in Figure 2—figure supplements 2–3. (B) Waves co-vary closely in the same side (left) and much less so between sides (right): a, best fit tangent; r, correlation coefficient. The insets show superimposed averaged waves (cal: 20 ms and 100 μV). (C) A string of Schaffer gamma shows unilateral waves in both sides (triangles). In paired bilateral waves, either side may lead (ovals). (D) Bilateral synchronization was measured from the start of the waves (time lag). The positive and negative values indicate that L or R waves led, respectively. R waves preceded more often (black bars), the bilateral lag being larger when R-waves were longer (line subplot in blue). (E) The amplitude difference between paired waves in the right and left sides is plotted against their time lag. Larger waves on any side had a tendency to lead. https://doi.org/10.7554/eLife.16658.005 Figure 2—source data 1 Spreadsheet containing measurements of the LFP generators and extracted waves for each experiment. Data are presented as the mean and s.e.m. for: cross- correlation index and τmax, amplitude and duration of extracted Schaffer and CA3som gamma waves, total number of paired waves (ipsilateral and bilateral), percentage of unilateral waves, covariation of amplitude and duration of bilateral waves, lag between start time of bilateral waves or ipsilateral paired waves, lags between paired waves in subgroups of longer waves in L, R, anterior or posterior sites, cross-correlation between Schaffer and CA3som waves, and the covariation index of amplitude and duration. The data pertain to Figures 2, Figure 2—figure supplement 2, Figure 4, and Figure 4—figure supplement 1. https://doi.org/10.7554/eLife.16658.006 Download elife-16658-fig2-data1-v2.xlsx Figure 2—source data 2 Schaffer LFP generators and extracted waves for the experiments used in Figures 2 and 4. https://doi.org/10.7554/eLife.16658.007 Download elife-16658-fig2-data2-v2.zip Gamma strings of tight left-right amplitude co-modulation between paired waves (Figure 2A and C) alternate with others of loose covariation (Figure 2—figure supplement 3). Therefore, we quantified the features of individual waves obtained through a deconvolution approach (see Figure 2—source data 1 and 2, and Materials and methods) and compared these between different sites. To avoid noisy LFP events, waves were only considered when they lasted >5 ms and reached >20 μV. The amplitude, duration and start time of individual Schaffer gamma waves reflect the size and synchronization of CA3 PC assemblies. Waves were designated as paired when they overlapped at two sites by at least 70% of their duration. Despite of a clear amplitude fluctuation at any site, paired waves were nearly identical along lamellar strips in one side (Figure 2A and B; covariance was ρA = 0.78 ± 0.02 for the amplitude and ρD = 0.63 ± 0.02 for the duration in La:Lp comparison), while they showed less co-variation between homotopic La-Ra sites (ρA = 0.5 ± 0.04 and ρD = 0.44 ± 0.03; see population statistics in Figure 2—figure supplement 2B,C). The matching waveforms and strong covariation of ipsilateral waves rule out the possibility that the modulation of amplitude over successive waves is due to a different site of origin of the waves and hence, the distance to the electrodes (Benito et al., 2014). Rather, it is consistent with a coarse lamellar-like distribution of Schaffer fibers in the CA1 for all waves, regardless of their amplitude. The mean wave duration was the same on both sides (R and L: 26.7 ± 0.7 ms; F(1,12) = 0, p=0.96). We found notable bilateral asymmetries. In particular, waves on the right side were larger in amplitude (Ra: 299 ± 11 µV; La: 237 ± 15 µV; F(1,12) = 12, p=0.005, n = 7 animals: Figure 2B–D). Interestingly, bilateral waves were rarely initiated synchronously. Although either side may lead (ovals in Figure 2C), it was more common that waves in the right side did so (55.6 ± 0.8% vs 44.4 ± 0.8% ). On average, the R waves preceded with similar values between anterior or posterior sites (Ra-La: 0.62 ± 0.14 ms; Rp-Lp: 0.67 ± 0.18 ms). We also found a notable proportion of unilateral waves (Figure 2C), with a higher incidence on the right side (R: 11.7 ± 2.4%; L: 5.5 ± 1%). These unilateral waves were smaller than bilateral ones in the right hemisphere (212 ± 20 µV; bilateral vs. unilateral: p=0.002), but not in the left one (192 ± 20 µV; p=0.09). To countercheck the overall primacy of Schaffer activity on one side we applied the Granger Causality (GC) test between the right and left Schaffer generators over 90 s epochs. Figure 3A shows R and L Schaffer activations in a representative experiment. The GC test confirmed that there are statistically significant and reciprocal relations between the R and L sides (Figure 3B: p=10–6 and p=10–8 for L to R and R to L relations, respectively). Moreover, the functional relation peaked in the low-gamma frequency band (30–50 Hz) and the right to left link was strongly dominant over time (Figure 3C,D). This result was verified for all seven animals. Figure 3 Download asset Open asset Assessment of functional asymmetry with Granger causality and phase relations. (A) A short epoch of activations of the right and left Schaffer pathways. (B) F-statistics for Granger Causality (GC) test revealing significant reciprocal influence from R to L and from L to R sides. (C) Frequency dependence of GC. R to L relation exhibits a peak at gamma frequency. (D) Time-frequency display of the GC index. R to L relationship is stronger and more persistent. (E) Distribution of phases in the L side with onsets related to zero phases in the R side, i.e., when field events begin. The mean phase lag of 0.22 rad (corresponding to 0.95 ms time lag) is highly significant. The population data is indicated in the text. https://doi.org/10.7554/eLife.16658.011 Although the GC test confirmed a preferred right to left directionality, it provided no time lag between the Schaffer activities. We crosschecked the lag obtained from the start times of the paired gamma waves using an additional test to evaluate the phase shift between the Schaffer activities. Figure 3E shows the histogram of the phases in Schaffer activity in the left side with onsets related to zero phases in the right side (corresponding to the beginning of LFP events in that side). The circular statistics confirmed the presence of a highly significant peak at Δϕ = 0.22 ± 0.04 radians. Thus, the right side indeed appears to lead the generation of activity in Schaffer pathways. By evaluating the mean frequency of the generators (~45 Hz) we can estimate the corresponding time lag Δt = 0.95 ± 0.2 ms, in a good agreement with the value obtained by the analysis of paired Schaffer waves (1.12 ms for this experiment). Again this result was verified in all seven animals (Δϕ = 0.12 ± 0.06 radians; Δt = 0.54 ± 0.26 ms), with the mean time lag being roughly equal to the τmax in the CCs. Variable ipsilateral dynamics subjects to global asymmetric bilateral coupling Since the duration of paired waves was not identical, we explored whether the leading site had any relation to the wave’s features. The more relevant results were obtained when paired left-right waves were sorted by the site at which they showed longer duration (L or R, anterior or posterior) (Figure 2B,D,E). Notably, the right-left lag was accentuated when R-waves were longer (a, p: 3.09 ± 0.06 and 3.03 ± 0.17 ms), whilst longer L-waves also led to righ-hand ones albeit by a smaller amount (a, p: 1.97 ± 0.13 and 1.91 ± 0.23 ms, n = 7, F(1,12) = 517, p<0.001) (Figure 2D, and Figure 2—figure supplement 2). The data from different individuals indicated that these lags were robust for different antero-posterior locations of the shanks or when there was a slight a-p displacement between the right and left sides (Figure 2—source data 1 and Figure 2—figure supplement 1). We also found a tendency towards a lead by longer and larger waves irrespective of the leading side (Figure 2E). These observations indicated an independent discharge by left and right CA3 assemblies that project to the anterior or posterior sites of CA1 indistinctly, while the overall lag towards the right-hand side supports a global right-to-left asymmetric entrainment. Such directionality is also supported by the fact that the mean lag from crossed Lp to Ra sites (1.13 ± 0.25 ms) was roughly equal to the accumulated lag from right to left plus the lag used by a-p axonal conduction: Ra→La (0.62 ± 0.14 ms), La→Lp (0.52 ± 0.1 ms). In turn, the La to Rp lag became balanced (–0.1 ± 0.24 ms) as expected if the righ-to-left lag were absorbed by the opposite sign of the a-p lag: La→Ra (-0.62 ± 0.14 ms), Ra→Rp (0.67 ± 0.33 ms). The preferred lead of longer/larger Schaffer gamma waves in either side might suggest that CA3 clusters on one side excite CA3 clusters on the other, which then set up delayed contralateral Schaffer waves in the CA1. We explored this possibility by estimating the minimum time used by CA3 spikes on one side to get to CA3 PCs through the latency of the contralateral CA3 antidromic population spike elicited from the septal pole of the Left CA3, which was 2.5 ± 0.1 ms (n = 6). We also estimated the shortest possible lag for the direct driving of CA3 to the contralateral CA1 through the latency of the evoked commissural fEPSP in CA1, which amounted 5.8 ± 0.3 ms (n = 7, i.e.: three-fold the L-R lag for spontaneous paired waves). These results leave some room for a reduced fraction of the bilateral waves to be explained by the inter-hippocampal excitatory driving of unilaterally ignited CA3 clusters, although the presence of numerous unilateral waves points to additional mechanisms. Notably, side-independent instigation of Schaffer waves was also found in intra-hippocampal a-p comparisons. Thus, while on average Schaffer waves led in anterior sites (0.52 ± 0.06 and 0.67 ± 0.33 ms for the L and R sides, respectively; L-R: F(1,12) = 0.3, p=0.6) in compliance with a global antero-posterior lamellar topology of Schaffer fibers, we found quite different lags depending on which a-p site had longer waves. For waves that were longer in anterior sites the a-p lag increased to 2.6 ± 0.3 and 2.2 ± 0.3 ms in the right and left sides, respectively (R-L: F(1,12) = 0.65, p=0.4; total vs. longer R: F(1,12) = 102, p<0.001). More notably, when posterior waves were longer they preceded anterior ones by 1.13 ± 0.5 and 1.8 ± 0.3 ms for the R and L sides, respectively (R-L: F(1,12) = 1.24, p=0.29; total vs. longer L: F(1,12) = 53, p<0.001). Thus the large CA3 PC assemblies initiate firing on any side and location, regardless of the overall bilateral coupling that maintains a global precedence on the right-hand side. Tight ipsilateral synchrony but weak bilateral entrainment characterizes the CA3 gamma waves in the soma layer To delve further into the mechanisms of bilateral entrainment of Schaffer gamma oscillations, we explored the ipsi- and bilateral expression of the gamma activity in the soma layer of the CA3 region itself, and its relationship to Schaffer activity (outgoing CA3 quanta). This so-called the CA3som generator is known to be part of a gamma pacemaker in this region (Traub et al., 1996; Fisahn et al., 1998; Bartos et al., 2002; Csicsvari et al., 2003; Hájos et al., 2004; Mann et al., 2005; Oren et al., 2006; Hájos and Paulsen, 2009; Pietersen et al., 2009; Gulyás et al., 2010; Mann and Mody, 2010; Kohus et al., 2016). The CA3som gamma-paced wavelets were recorded over 1 to 3 contiguous electrodes in different animals and they appeared as positive non-overlapping events riding on a flat baseline (Figure 1C and Figure 1—figure supplement 1B). Ipsilateral comparisons of CA3som LFPs between anterior and posterior sites in the two sides were only possible in two animals (see Figure 4 for an illustrative experiment), although partial comparisons were obtained in another four. The data were pooled by side (La-Lp and Ra-Rp: n = 7) or position (La-Ra and Lp-Rp: n = 8), and like the Sch LFPs, the CA3som LFPs displayed close-fitting within-side activities, whereas bilateral synchrony was far less marked and mismatches of individual waves were more frequent (unilateral CA3som waves: 22 ± 1.2 and 26 ± 2.3% for the L and R sides, respectively; Figure 4A, La-Lp vs. Lp-Rp traces). Accordingly, the antero-posterior wide band coherence gave significant values for frequencies above 25 Hz in all cases, whilst none gave significant values for bilateral comparisons (Figure 4A, spectral coherence plots). The CCs behaved similarly (a-p: 0.66 ± 0.6; L-R: 0.27 ± 0.02; F(1,12) = 32, p<0.001, with a non-significant phase difference between a-p comparisons (τmax: 0.1 ± 0.2 ms), but similar to Schaffer activity in R-L comparisons (0.42 ± 0.8 ms). The comparisons between extracted CA3som gamma waves yielded similar results as that for Schaffer activity (Figure 4—figure supplement 1A). Thus, the amplitude covariance of bilateral waves was stronger in intra (ρA = 0.62 ± 0.06) than interhippocampal waves (ρA = 0.24 ± 0.04; F(1,14) = 42, p<0.001), although the amplitude did not differ in the left and right hemispheres (La: 162 ± 26; Ra: 183 ± 28 μV; (F(1,10) = 0.32, p=0.58). Also, on average R-waves led by 0.34 ± 0.1 ms (n = 8), and this lag increased to 2.72 ± 0.01 ms when the R-waves were longer (total vs. longer R: F(1,14) = 297, p<0.001), and longer L-waves also preceded the right-hand ones by 2.28 ± 0.02 ms (total vs. longer L: F(1,14) = 643, p<0.001; (Figure 2—source data 1), matching the relationships to the Schaffer waves. Figure 4 with 1 supplement see all Download asset Open asset CA3som gamma activity has weak bilateral coherence but is coupled to ipsilateral Schaffer. (A) Comparison of CA3som activities between pairs of sites. The histograms of spectral coherence only show significant values (blue) for ipsilateral comparisons. The sample traces show tight matching in superimposed activities at a-p sites (upper traces) and frequent mismatch in bilateral comparisons in the same epoch (lower traces). Cyan and black traces correspond to the left and right sides. (B) Comparisons between Schaffer and CA3som activities (blue and maroo" @default.
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• W4250069235 title "Decision letter: The right hippocampus leads the bilateral integration of gamma-parsed lateralized information" @default.
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