Limits...
A hippocampal network for spatial coding during immobility and sleep

View Article: PubMed Central - PubMed

ABSTRACT

How does an animal know where it is when it stops moving? Hippocampal place cells fire at discrete locations as subjects traverse space, thereby providing an explicit neural code for current location during locomotion. In contrast, during awake immobility, the hippocampus is thought to be dominated by neural firing representing past and possible future experience. The question of whether and how the hippocampus constructs a representation of current location in the absence of locomotion has stood unresolved. Here we report that a distinct population of hippocampal neurons, located in the CA2 subregion, signals current location during immobility, and furthermore does so in association with a previously unidentified hippocampus-wide network pattern. In addition, signaling of location persists into brief periods of desynchronization prevalent in slow-wave sleep. The hippocampus thus generates a distinct representation of current location during immobility, pointing to mnemonic processing specific to experience occurring in the absence of locomotion.

No MeSH data available.


Locomotor STAs and theta analysisUnit spiking at speeds >4 cm/s was analyzed. a, Locomotor STAs. Plotted are mean STAs of hippocampal LFP for each principal unit population. LFP from four distinct recording sites (REF, CA2, CA3, DG) are plotted in rows. Vertical lines correspond to the time of spiking. The width of the trace indicates ± s.e.m. across individual unit STAs. The total trace length is 2 s. REF: reference electrode located in corpus callosum overlying dorsal hippocampus, reporting signals relative to a cerebellar ground screw. Scale bars: x: 250 ms, y: 50 μV. b, Theta phase locking analysis of each principal unit population. For comparison of theta phase preferences between unit populations in simultaneously recorded data, analysis was restricted to subjects in which all four unit types (CA1, CA3, CA2 N and CA2 P) were recorded. First row: mean circular distribution of spikes for each unit population. Error bars: ± s.e.m. across individual units. Second row: the distribution of mean circular phases for significantly modulated units (p < 0.05, Rayleigh tests, total number of significant units reported at upper right). Bottom row: the distribution of modulation depths (resultant length) for all units. In plots with theta phase (bin size: 15°; troughs at 180°, indicated in dotted lines), two cycles are shown to aid visual comparison. Surprisingly, we did not observe a ∼90° phase lead of CA3 relative to CA1 as reported in a previous study32, perhaps due to differences in CA3 recording locations.
© Copyright Policy
Related In: Results  -  Collection


getmorefigures.php?uid=PMC5037107&req=5

Figure 6: Locomotor STAs and theta analysisUnit spiking at speeds >4 cm/s was analyzed. a, Locomotor STAs. Plotted are mean STAs of hippocampal LFP for each principal unit population. LFP from four distinct recording sites (REF, CA2, CA3, DG) are plotted in rows. Vertical lines correspond to the time of spiking. The width of the trace indicates ± s.e.m. across individual unit STAs. The total trace length is 2 s. REF: reference electrode located in corpus callosum overlying dorsal hippocampus, reporting signals relative to a cerebellar ground screw. Scale bars: x: 250 ms, y: 50 μV. b, Theta phase locking analysis of each principal unit population. For comparison of theta phase preferences between unit populations in simultaneously recorded data, analysis was restricted to subjects in which all four unit types (CA1, CA3, CA2 N and CA2 P) were recorded. First row: mean circular distribution of spikes for each unit population. Error bars: ± s.e.m. across individual units. Second row: the distribution of mean circular phases for significantly modulated units (p < 0.05, Rayleigh tests, total number of significant units reported at upper right). Bottom row: the distribution of modulation depths (resultant length) for all units. In plots with theta phase (bin size: 15°; troughs at 180°, indicated in dotted lines), two cycles are shown to aid visual comparison. Surprisingly, we did not observe a ∼90° phase lead of CA3 relative to CA1 as reported in a previous study32, perhaps due to differences in CA3 recording locations.

Mentions: In contrast to STAs from locomotor periods (characterized by the expected ∼8 Hz theta frequency modulation18,32, Extended Data Fig. 6), STAs from non-SWR immobility periods (Fig. 4b, c, Extended Data Fig. 7a) showed that N units fired at the time of a positive transient LFP pattern lasting ∼200 ms. The pattern was smallest on the parent electrode in CA2, larger in CA3, and largest at DG, suggesting broad engagement of the hippocampal circuit. Furthermore, unlike N units, P units showed a mean STA characterized by a negative transient similar to the canonical sharp wave transient of SWRs33 (Fig. 4b, c).


A hippocampal network for spatial coding during immobility and sleep
Locomotor STAs and theta analysisUnit spiking at speeds >4 cm/s was analyzed. a, Locomotor STAs. Plotted are mean STAs of hippocampal LFP for each principal unit population. LFP from four distinct recording sites (REF, CA2, CA3, DG) are plotted in rows. Vertical lines correspond to the time of spiking. The width of the trace indicates ± s.e.m. across individual unit STAs. The total trace length is 2 s. REF: reference electrode located in corpus callosum overlying dorsal hippocampus, reporting signals relative to a cerebellar ground screw. Scale bars: x: 250 ms, y: 50 μV. b, Theta phase locking analysis of each principal unit population. For comparison of theta phase preferences between unit populations in simultaneously recorded data, analysis was restricted to subjects in which all four unit types (CA1, CA3, CA2 N and CA2 P) were recorded. First row: mean circular distribution of spikes for each unit population. Error bars: ± s.e.m. across individual units. Second row: the distribution of mean circular phases for significantly modulated units (p < 0.05, Rayleigh tests, total number of significant units reported at upper right). Bottom row: the distribution of modulation depths (resultant length) for all units. In plots with theta phase (bin size: 15°; troughs at 180°, indicated in dotted lines), two cycles are shown to aid visual comparison. Surprisingly, we did not observe a ∼90° phase lead of CA3 relative to CA1 as reported in a previous study32, perhaps due to differences in CA3 recording locations.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC5037107&req=5

Figure 6: Locomotor STAs and theta analysisUnit spiking at speeds >4 cm/s was analyzed. a, Locomotor STAs. Plotted are mean STAs of hippocampal LFP for each principal unit population. LFP from four distinct recording sites (REF, CA2, CA3, DG) are plotted in rows. Vertical lines correspond to the time of spiking. The width of the trace indicates ± s.e.m. across individual unit STAs. The total trace length is 2 s. REF: reference electrode located in corpus callosum overlying dorsal hippocampus, reporting signals relative to a cerebellar ground screw. Scale bars: x: 250 ms, y: 50 μV. b, Theta phase locking analysis of each principal unit population. For comparison of theta phase preferences between unit populations in simultaneously recorded data, analysis was restricted to subjects in which all four unit types (CA1, CA3, CA2 N and CA2 P) were recorded. First row: mean circular distribution of spikes for each unit population. Error bars: ± s.e.m. across individual units. Second row: the distribution of mean circular phases for significantly modulated units (p < 0.05, Rayleigh tests, total number of significant units reported at upper right). Bottom row: the distribution of modulation depths (resultant length) for all units. In plots with theta phase (bin size: 15°; troughs at 180°, indicated in dotted lines), two cycles are shown to aid visual comparison. Surprisingly, we did not observe a ∼90° phase lead of CA3 relative to CA1 as reported in a previous study32, perhaps due to differences in CA3 recording locations.
Mentions: In contrast to STAs from locomotor periods (characterized by the expected ∼8 Hz theta frequency modulation18,32, Extended Data Fig. 6), STAs from non-SWR immobility periods (Fig. 4b, c, Extended Data Fig. 7a) showed that N units fired at the time of a positive transient LFP pattern lasting ∼200 ms. The pattern was smallest on the parent electrode in CA2, larger in CA3, and largest at DG, suggesting broad engagement of the hippocampal circuit. Furthermore, unlike N units, P units showed a mean STA characterized by a negative transient similar to the canonical sharp wave transient of SWRs33 (Fig. 4b, c).

View Article: PubMed Central - PubMed

ABSTRACT

How does an animal know where it is when it stops moving? Hippocampal place cells fire at discrete locations as subjects traverse space, thereby providing an explicit neural code for current location during locomotion. In contrast, during awake immobility, the hippocampus is thought to be dominated by neural firing representing past and possible future experience. The question of whether and how the hippocampus constructs a representation of current location in the absence of locomotion has stood unresolved. Here we report that a distinct population of hippocampal neurons, located in the CA2 subregion, signals current location during immobility, and furthermore does so in association with a previously unidentified hippocampus-wide network pattern. In addition, signaling of location persists into brief periods of desynchronization prevalent in slow-wave sleep. The hippocampus thus generates a distinct representation of current location during immobility, pointing to mnemonic processing specific to experience occurring in the absence of locomotion.

No MeSH data available.