Skip to main page content
Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
. 2018 Mar 28;38(13):3287-3302.
doi: 10.1523/JNEUROSCI.1814-17.2018. Epub 2018 Feb 27.

Testing the Efficacy of Single-Cell Stimulation in Biasing Presubicular Head Direction Activity

Affiliations
Free PMC article

Testing the Efficacy of Single-Cell Stimulation in Biasing Presubicular Head Direction Activity

Stefano Coletta et al. J Neurosci. .
Free PMC article

Abstract

To support navigation, the firing of head direction (HD) neurons must be tightly anchored to the external space. Indeed, inputs from external landmarks can rapidly reset the preferred direction of HD cells. Landmark stimuli have often been simulated as excitatory inputs from "visual cells" (encoding landmark information) to the HD attractor network; when excitatory visual inputs are sufficiently strong, preferred directions switch abruptly to the landmark location. In the present work, we tested whether mimicking such inputs via juxtacellular stimulation would be sufficient for shifting the tuning of individual presubicular HD cells recorded in passively rotated male rats. We recorded 81 HD cells in a cue-rich environment, and evoked spikes trains outside of their preferred direction (distance range, 11-178°). We found that HD tuning was remarkably resistant to activity manipulations. Even strong stimulations, which induced seconds-long spike trains, failed to induce a detectable shift in directional tuning. HD tuning curves before and after stimulation remained highly correlated, indicating that postsynaptic activation alone is insufficient for modifying HD output. Our data are thus consistent with the predicted stability of an HD attractor network when anchored to external landmarks. A small spiking bias at the stimulus direction could only be observed in a visually deprived environment in which both average firing rates and directional tuning were markedly reduced. Based on this evidence, we speculate that, when attractor dynamics become unstable (e.g., under disorientation), the output of HD neurons could be more efficiently controlled by strong biasing stimuli.SIGNIFICANCE STATEMENT The activity of head direction (HD) cells is thought to provide the mammalian brain with an internal sense of direction. To support navigation, the firing of HD neurons must be anchored to external landmarks, a process thought to be supported by associative plasticity within the HD system. Here, we investigated these plasticity mechanisms by juxtacellular stimulation of single HD neurons in vivo in awake rats. We found that HD coding is strongly resistant to external manipulations of spiking activity. Only in a visually deprived environment was juxtacellular stimulation able to induce a small activity bias in single presubicular neurons. We propose that juxtacellular stimulation can bias HD tuning only when competing anchoring inputs are reduced or not available.

Keywords: cortical physiology; head direction cell; in vivo electrophysiology; single-cell stimulation; spatial navigation.

Figures

Figure 1.
Figure 1.
Juxtacellular recordings of presubicular HD neurons in head-fixed rats. A, Schematic representation of the Open recording configuration, consisting of a head-fixed rat on a rotating platform in the presence of a rich set of proximal and distal cues (see also Preston-Ferrer et al., 2016). B, Reconstruction of the dendritic (blue) and axonal morphology (red) of a layer 3 pyramidal HD cell recorded in a head-fixed rat. The axon is truncated for display purposes. The borders of the presubicular layers are indicated (L1–L6). Bottom, Polar plot showing the directional tuning for the representative reconstructed cell. Peak firing rate and HD index are indicated. Scale bar, 100 μm. C, Schematic outline of parasagittal sections through the rat brain at three mediolateral extents of the dorsal PreS (gray): medial (top), intermediate (middle), and lateral (bottom) (see Materials and Methods for details). The locations of reconstructed tracks through the PreS (color lines) and identified cells (color dots) are represented in different colors for three representative brains (the number of recovered tracks of penetration attempts are indicated). Green arrowheads indicate the two representative tracks shown in D. WM, White matter (angular bundle), Sub, subiculum, RS, retrosplenial cortex, PaS, parasubiculum. Scale bar, 500 μm. D, Left, Parasagittal section stained for calbindin (green) and neurobiotin (red) showing two electrode tracks (white arrowheads) through the dorsal PreS. In the anterior penetration, spillover of Neurobiotin was performed to aid anatomical recovery of the track (see details in Materials and Methods). Right, Same section stained for NeuN (the two tracks are indicated by the arrowheads).WM, White matter (angular bundle), Sub, subiculum, RS, retrosplenial cortex. Scale bars, 200 μm.
Figure 2.
Figure 2.
Single-cell stimulation in a cue-rich familiar environment. A, Top, Schematic representation of the Open recording configuration consisting of a head-fixed rat on a rotating platform in the presence of a rich set of proximal and distal cues (see also Preston-Ferrer et al., 2016). Middle, Polar plot showing firing rate as a function of HD for a representative PreS HD neuron recorded during passive rotation. Peak firing rate and HD index are indicated. Bottom, High-pass-filtered spike trace for the HD cell recording shown above. B, Same as A but for juxtacellular stimulation (STIM) at ∼150° away from the preferred direction. The polar plot (middle) indicates the stimulus direction (red line). Bottom, High-pass-filtered voltage trace showing a spike train evoked by a brief juxtacellular current injection (see Materials and Methods). The onset of current injection is indicated by the lightning bolt symbol. The asterisk indicates stimulus artifact, truncated for display purposes. C, Same as in A but after the juxtacellular stimulation shown in B. Note that HD tuning remained largely unchanged compared with before stimulation (A). D, Raster plot (top) and average firing rate histogram (bottom) for all spike trains evoked in HD neurons under passive rotation (n = 130 stimulations in 81 neurons). Recordings are aligned by the first spike of the evoked stimulus train (lightning bolt symbol). For display purposes, all stimulations are shown in the raster plot; however, multiple stimulations within individual neurons were averaged before being entered into the firing rate histogram so that each cell contributed one data point. E, Scatterplot showing preferred directions computed before and after the stimulation. Red line indicates the identity line. The red and green circles correspond to the representative examples shown in AC and H, respectively. The number of cells and the p-value (Wilcoxon signed-rank test) are indicated. F, Cumulative probability plot showing the correlation coefficients for HD tuning curves computed before and after stimulation (black) and for the two halves of the recordings before stimulation (gray). The number of cells and the p-value are indicated. G, Scatter plot showing Δ preferred directions (i.e., preferred direction after stimulation-preferred direction before stimulation) as a function of the stimulus distance from the preferred direction (i.e., preferred direction-STIM direction). The red and green circles correspond to the representative examples shown in AC and H, respectively. The linear regression line (red), the correlation coefficient (r), the number of cells, and the p-value are indicated. H, Polar plots showing the activity of another HD cell before and after the stimulation (rotated by 45° for display purposes). Dotted lines indicate the 30° interval centered on the stimulus direction (red line) used for computing the Q ratios (see I and text for more details). Peak firing rates and HD indices are indicated. I, Scatterplot showing the Q ratios (i.e., the ratios between the average firing rate within and outside a 30° interval centered on the stimulus direction) computed for all cells before and after the stimulation. The red and green circles correspond to the representative examples shown in AC and H, respectively. Red line indicates the identity line and the blue line on the top histogram represents the median. The number of cells and the p-value (Wilcoxon signed-rank test) are indicated. More details about the stimulation procedures can be found in Figures 2-1 and 2-2.
Figure 3.
Figure 3.
Unstable HD activity in the presence of a single proximal visual cue. AC, Top, Schematic representation of the recording protocol in which the activity of the neurons (n = 69) was sequentially monitored in the Open (A, Open_1) and Closed (B) configuration. For a subset of neurons (n = 23), the activity was monitored in the Open configuration again (C, Open_2). Note the presence of a cylinder surrounding the animal and a single proximal visual cue (LED) in the Closed configuration. Bottom, Polar plots showing firing rate as a function of HD for a representative HD cell recorded sequentially in the Open_1, Closed, and Open_2 configurations. Peak and average firing rates and HD indices are indicated. D, Spike trajectory plot showing the angular HD as a function of time for the same cell shown in AC. Spikes (black dots) are indicated. The dotted red line indicates the transition across the different configurations. Note the sharp HD tuning of the cell in both Open Configurations (Open_1 and Open_2) compared with the Closed configuration (Closed). E, Color-coded distribution of preferred direction for all HD cells (n = 69) recorded sequentially in the Open (left) and Closed (right) configurations. Each row represents the firing rate of a single neuron (normalized relative to its peak firing rate; red) ordered by the location of their peak firing rates relative to the rat's HD in the Open Configuration. F, Polar plots showing the activity of representative “stable” and “unstable” HD cells sequentially recorded in the Open and the Closed configuration. Peak and average firing rates and HD indices are indicated. G, Average firing rates and HD indices computed in the Open and Closed configuration (n = 69 neurons, gray lines). Black lines indicate the averages. Error bars indicate SEM. p-values are indicated (Wilcoxon signed-rank test). H, Cumulative probability plot showing the correlation coefficients of HD tuning curves for the Open_1 versus Closed configuration (gray) and for the Open_1 versus Open_2 configuration (black). The number of cells and the p-value (Wilcoxon signed-rank test) are indicated. I, HD indices computed in the Open_1, Closed, and Open_2 configurations (n = 23 neurons, gray lines). Black line indicates the average. Error bars indicate SEM. p-values are indicated (Wilcoxon signed-rank test; Bonferroni correction for multiple comparisons).
Figure 4.
Figure 4.
Extracellular recordings of visual responses in the PreS of anesthetized rats. A, Schematic representation of the experimental configuration. Multiunit extracellular recordings were performed in anesthetized rats while light-flash stimuli (2 s) were presented to the contralateral eye (see Materials and Methods for details). B, Parasagittal section through the dorsal PreS stained for calbindin (green; top) and cytochrome-oxidase activity (bottom). The electrolytic lesion site (dotted line), corresponding to the location of the extracellular recording shown in C, is indicated by the arrowhead. WM, White matter (angular bundle); Sub, subiculum; RS, retrosplenial cortex. Scale bars, 200 μm. C, Top, Representative high-pass filtered voltage trace showing the increase in multiunit activity evoked by the visual stimulus. The duration of the stimulation presentation (light) is outlined by the gray bar (2 s). The raster plot (middle) and the peristimulus time histogram (bottom) for all stimulation trials (n = 28) are shown. D, Average firing rates computed for 0.5 s before (baseline) and 0.5 after (Stim ON) the onset of the visual stimulus (n = 14 neurons). Black line indicates the average, blue line the recording shown in C. Error bars indicate SEM. p-value is indicated (Wilcoxon signed-rank test).
Figure 5.
Figure 5.
HD cell realignment after cue rotations. A, Schematic drawing showing the recording protocol for 90° cue rotations (LED1→LED2 and LED2→LED1). Cue rotations were interleaved with brief dark phases (see Materials and Methods for details). B, Angular HD as a function of time for a representative HD cell recorded following the protocol shown in A. Spikes (black dots) are indicated. Note the consistent shift of the neuron's preferred direction upon cue rotations (LED1→LED2 and LED2→LED1). C, Polar plots showing firing rates as a function of HD computed for LED1 (left), LED2 (middle), and the return to LED1 (right) for the same cell shown in B. Preferred directions (red arrows) and peak firing rates are indicated. D, Scatter diagrams showing the amount of angular shift of preferred directions between LED1 and LED2 configurations. Each dot represents a single cell (n = 11). The preferred directions shown by all cells in the LED1 configuration are aligned at 0°; therefore, those shown during the LED2 configuration are represented clockwise (because LED2 was placed 90° clockwise with reference to LED1). The average angle is indicated by the red arrow.
Figure 6.
Figure 6.
Single-cell stimulation under “instability” of the HD system. A, Top, Schematic representation of the Open recording configuration consisting of a head-fixed rat on a rotating platform in the presence of a rich set of proximal and distal cues. Middle, Polar plot showing firing rate as a function of HD for a representative PreS HD neuron recorded during passive rotation. Peak and average firing rates and HD indices are indicated. Bottom, High-pass-filtered spike trace for the HD cell recording shown above (scale bars as in D). B, Same as A but for the Closed recording configuration. C, Same as A but for juxtacellular stimulation (STIM). The polar plot (middle) indicates the stimulus direction (red line). Bottom, High-pass filtered voltage trace showing a spike train evoked by a brief juxtacellular current injection (see Materials and Methods). The onset of current injection is indicated by the lightning bolt symbol. The asterisk indicates stimulus artifacts truncated for display purposes. Scale bars are as in D. D, Same as in B but after the juxtacellular stimulation shown in C. Note the redistribution of firing around the stimulus direction (red line). E, Raster plot (top) and average firing rate histogram (bottom) for all spike trains evoked in PreS neurons under passive rotation (n = 42 stimulations in 25 neurons). Recordings are aligned by the first spike of the evoked stimulus train (lightning bolt symbol). For display purposes, all stimulations are shown in the raster plot; however, multiple stimulations within individual neurons were averaged before being entered into the firing rate histogram, so that each cell contributed one data point. F, Polar plots showing the activity of another HD cell in the Open and before and after the stimulation (HD indices: Open, 0.65; before STIM, 0.07; after STIM, 0.61; average firing rates: Open, 2.9 Hz; before STIM, 1.4 Hz; after STIM, 1.2 Hz; peak firing rates are indicated). Dotted lines indicate the 30° interval centered on the stimulus direction (red line) used for computing the Q ratios (see G and text for more details). G, Scatterplot showing the Q ratios (i.e., the ratios between the average firing rate within and outside a 30° interval centered on the stimulus direction) computed for all cells before and after the stimulation. The red and green circles correspond to the representative examples shown in AD and (F), respectively. Red line indicates the identity line, blue cross the mean ± SEM, and blue line the mean. The number of cells and the p-value (Wilcoxon signed-rank test) are indicated. H, Graph showing the subtraction of the average normalized tuning curves computed before and after stimulation (After STIM-Before STIM) aligned at the stimulus direction (0°). Note that a peak becomes apparent around the stimulus direction (red line). Dashed lines show SEM. I, Shuffled distribution of COM shifts (gray) computed by randomly shuffling individual recording epochs before and after stimulation (see details in Materials and Methods). The observed COM shift for the STIM-Closed dataset (vertical line) and the corresponding p-value are indicated. J, Box pots showing the Q ratios computed before and after stimulation for each dataset (STIM-Open, STIM-Closed, and No-STIM). Whiskers represent 1.5 IQR. Outliers are not shown for display purposes. p-values are indicated (Wilcoxon signed-rank test). More details about the STIM-Closed and No-STIM datasets can be found in Table 1.

Similar articles

See all similar articles

Publication types

LinkOut - more resources

Feedback