The Orienting Reflex Reveals Behavioral States Set by Demanding Contexts: Role of the Superior Colliculus

Abstract

Sensory stimuli can trigger an orienting reflex (response) by which animals move the head to position their sensors (e.g., eyes, pinna, whiskers). Orienting responses may be important to evaluate stimuli that call for action (e.g., approach, escape, ignore), but little is known about the dynamics of orienting responses in the context of goal-directed actions. Using mice of either sex, we found that, during a signaled avoidance action, the orienting response evoked by the conditioned stimulus (CS) consisted of a fast head movement containing rotational and translational components that varied substantially as a function of the behavioral and underlying brain states of the animal set by different task contingencies. Larger CS-evoked orienting responses were associated with high-intensity auditory stimuli, failures to produce the appropriate signaled action, and behavioral states resulting from uncertain or demanding situations and the animal's ability to cope with them. As a prototypical orienting neural circuit, we confirmed that the superior colliculus controls and codes the direction of spontaneous exploratory orienting movements. In addition, superior colliculus activity correlated with CS-evoked orienting responses, and either its optogenetic inhibition or excitation potentiated CS-evoked orienting responses, which are likely generated downstream in the medulla. CS-evoked orienting responses may be a useful probe to assess behavioral and related brain states, and state-dependent modulation of orienting responses may involve the superior colliculus.SIGNIFICANCE STATEMENT Humans and other animals produce an orienting reflex (also known as orienting response) by which they rapidly orient their head and sensors to evaluate novel or salient stimuli. Spontaneous orienting movements also occur during exploration of the environment in the absence of explicit, salient stimuli. We monitored stimulus-evoked orienting responses in mice performing signaled avoidance behaviors and found that these responses reflect the behavioral state of the animal set by contextual demands and the animal's ability to cope with them. Various experiments involving the superior colliculus revealed a well-established role in spontaneous orienting but only an influencing effect over orienting responses. Stimulus-evoked orienting responses may be a useful probe of behavioral and related brain states.

Keywords: avoidance; behavioral states; escape; midbrain; orienting.

Figure 1.

CS-evoked orienting responses in the context of signaled active avoidance. A, Arrangement of the shuttle box used during signaled avoidance tasks. B, Schematic represents the timing of avoidance, escape, and intertrial intervals during the three avoidance procedures (AA1, AA2, and AA3). AA1 and AA2 are signaled avoidance tasks, where ITCs are punished in AA2. AA3 is a discrimination procedure. CS2 (4 kHz) in AA3 signals to passively avoid (“do not cross or get US, if you cross”), while CS1 (8 kHz) signals to actively avoid (“cross or get US when the escape interval begins, if you don't cross”). C, CS-evoked orienting response measured by tracking overall head speed. The orienting response is triggered by the onset of the auditory stimulus that signals the avoidance interval. The orienting response movement is followed by the avoidance movement (i.e., when the animal moves to avoid the US). The traces show the first training session (black) and the fifth session (red) for naive mice trained in AA1. Right, Close-up of the left panel. D, Rotational and translational components of the overall head speed shown in C. E, Linear (forward) and sideways components of the translational movements shown in D. Overall head tilt is also shown.

Figure 2.

CS-evoked orienting responses habituate as naive mice learn the AA1 signaled active avoidance procedure. A, Behavioral performance during five AA1 sessions showing the percentage of active avoids (black circles), avoidance latency (orange triangles), and number of ITCs (gray bars). B, Baseline (−0.5 to 0 s window vs CS onset), orienting response (0-0.5 s window), and avoidance response (0.5-5 s) measured as overall, rotational, and translational movement speed (cm/s in all figures). Orienting and avoidance movements are corrected by the baseline movement. Orienting responses were large on the first training session but habituated rapidly as mice acquired signaled avoidance. Population data and traces are mean ± SEM in all figures.

Figure 3.

CS-evoked orienting responses vary in association with the behavioral states set by No US, AA1, AA2, and AA3 procedures. A, Behavioral performance during the different procedures (panel details are as per Fig. 1). B, Baseline and orienting response (overall) movement, including the rotational and translational components of the orienting response during the different procedures. C, Overall head movement traces for different procedures. D, The rotational and translational components of the traces shown in C.

Figure 4.

CS-evoked orienting responses depend on SPL and prepare for the ensuing action. A, Head speed traces evoked by the CS1 (8 kHz) and CS2 (4 kHz) pips, including the CS1 and CS2 proper during performance of AA3. Auditory pips were evoked at three different SPLs for the CS1 and CS2 frequencies. B, Head speed traces of CS1 and CS2 trials in which mice performed the correct response (active avoids for CS1 and passive avoids for CS2) or the incorrect response (escapes for CS1 and errors for CS2). C, Population measures of the orienting responses (Max and Min) evoked by the pips shown in A decomposed into rotational and translational movement components. *p < 0.05, significant differences between pips at the same frequency or between frequencies. Rightward panels represent the same measures for avoidance trials classified as correct versus incorrect responses during AA1/AA2 or CS1 in AA3 (Active avoids vs Escapes), and CS2 in AA3 (Passive avoids vs Errors). These populations measures compare the CS-evoked orienting responses shown in B. *p < 0.05, significant differences between the correct and incorrect responses. ^#The differences for all trials (unclassified) between CS1 and CS2.

Figure 5.

During signaled active avoidance, the CS-evoked orienting response orients the head toward the escape route. Change in distance from the forward-looking head marker (nose) to the speaker or the door during signaled active avoidance trials. Negative indicates that the distance toward the noted location was reduced during the orienting response. Shown are all trials, and those trials classified as avoids or escapes. *p < 0.05, significant change.

Figure 6.

CS-evoked orienting responses are associated with superior colliculus activation measured with calcium imaging fiber photometry. A, Parasagittal section showing the optical fiber tract reaching superior colliculus and GCaMP6f fluorescence expressed in CaMKII neurons around the fiber ending. The main panel blends a dark-field image of the section with the green channel of the GCaMP6f fluorescent image. Inset, Close-up of the fluorescent image (green and blue DAPI channels) without blending with the dark-field image. B, Cross-correlation between head movement and superior colliculus F/F_o for the rotational and translational components. C, Linear fit (correlation, r) between overall head movement and superior colliculus F/F_o, including the rotational and translational components. D, Traces of F/F_o and head movement rotational and translational components evoked by the CS during AA1/AA2 (left panels) and CS1/CS2 trials during AA3. In these mice, the CS2 tone had a lower SPL (60-65 dB) than the regular CS2 tone, and did not evoke a noticeable inhibitory component. E, Per trial correlations between orienting response overall, rotational, and translational movements with superior colliculus F/F_o. Lines indicate the linear fits between the measured variables before (red) and after scrambling one of them (gray). The correlation of the red line fit is significant (p < 0.0001), but the gray line is not.

Figure 7.

Schematic of the different optogenetic groups of mice used in the present study to inhibit (A) or excite (B) the superior colliculus. Blue represents blue light and expression of ChR2. Green represents green light and expression of Arch. As noted, opsin expression occurs in GABAergic (Vgat), glutamatergic (Vglut or CaMKII), or cholinergic (Chat) afferents and/or local neurons in the superior colliculus. The GABAergic afferents originated in SNr. Light was always applied by optical fibers implanted within the superior colliculus. C, PSTHs represent unit firing in superior colliculus (SC) recorded from an implanted optrode in freely moving Vgat-ChR2 mice. Application of blue light (500 ms) into superior colliculus inhibited spontaneous firing. The inhibition was stronger for continuous blue light than for trains at 20 or 40 Hz (10 ms pulses in the trains). D, Population analysis of the data shown in C.

Figure 8.

Altering CS-evoked superior colliculus activation with optogenetic inhibition or excitation enhances CS-evoked orienting responses during AA1. A, Optogenetic inhibition of the superior colliculus during the CS presentation enhanced overall, rotational, and translational movements of CS-evoked orienting responses compared with CS alone trials. Bottom, Behavioral performance. *p < 0.05, optogenetic versus natural CS trials within the same sessions. B, When optogenetic inhibition of the superior colliculus was used as a CS (without the natural tone CS), the animals sustained high levels of avoidance responses (albeit at lower levels than the natural CS) and the orienting responses evoked by inhibiting the superior colliculus were slightly larger in overall, rotational, and translational movement compared with the orienting responses evoked by the natural CS. C, D, Same as per A, B, but the optogenetic manipulations excited superior colliculus neurons. The orienting responses evoked by the optogenetic stimulation were larger than the orienting responses evoked by the natural CS. However, the enhancement of orienting responses evoked by exciting superior colliculus involved mostly translational, not rotational, components. Although superior colliculus excitation was an effective signal to avoid the US, performance was worse than when the natural CS was used. E, Example orienting response traces showing rotational (red and dashed black) and translational (blue and dashed cyan) movements for the procedure in B. Dashed traces represent optogenetic inhibition of the superior colliculus used as a CS. Continuous traces represent the natural auditory CS. Note the larger dashed traces. F, Example orienting response traces represent rotational (red and dashed black) and translational (blue and dashed cyan) movements for the procedure in D. Dashed traces represent optogenetic excitation of the superior colliculus used as a CS. Continuous traces represent the natural auditory CS. Note the larger translational orienting movement during optogenetic excitation (dashed cyan) compared with the natural CS (blue). Left, The traces on the right expanded in both axes. This reveals a shift of the translational avoidance movement to the left (sooner) when it is evoked by superior colliculus excitation (dashed cyan) compared with the natural CS (blue).

Figure 9.

Population superior colliculus neuron activity measured with calcium imaging fiber photometry reveals the direction of spontaneous exploratory orienting movements. A, F/F_o calcium imaging, head turn bias, and head speed traces classified by the turning direction (ipsiversive and contraversive) versus the side of the recording (implanted optical fiber). At time 0, the animals spontaneously turn the head in the indicated direction. Columns represent all head turns (left), those that included a previous turn within 1 s (middle), and those that were devoid of a previous turn within 1 s (right). The speeds of the movements were similar in both directions. B, Population measures (peak amplitude and time to peak) of the F/F_o signal before (pre-) and after (post-) movement onset (zero in A) for >1 s turns (to reduce the impact of previous turns). The negative valley was measured around movement onset. *p < 0.05, between both directions.

Figure 10.

Superior colliculus unit activity measured with electrophysiology reveals two groups of neurons that predict spontaneous exploratory orienting movements. A, PSTH of unit firing (Hz), head turn bias, and speed traces classified by the turning direction (ipsiversive and contraversive) versus the side of the recording microelectrodes for >1 s turns. At time 0, the animals spontaneously turned their head in the indicated direction. The speeds of the movements were similar in both directions. B, Units shown in A classified with principal component analysis as Group 1 (75% of units) and Group 2 (25% of units) have two different firing patterns during the movements. C, Population measures of unit firing for Group 1 and Group 2 neurons. Bottom, The firing corrected by the baseline firing. *p < 0.05, significant differences between both directions. ^#p < 0.05, significant differences between both groups of units. D, A selected group of very well-isolated single units (n = 17) from the population of recorded units all fall within the Group 1 category.

Figure 11.

Optogenetic inhibition of the superior colliculus biases ipsiversively spontaneous exploratory orienting movements. A, Each panel overlays the effects of trains (blue only) or continuous (blue or green) light on head bias (angle in degrees), and rotational and translational movement components (speed, cm/s) during exploration of an open field for the different groups used to inhibit the superior colliculus (noted in Fig. 7A), including No Opsin controls. B, Population measures of peak head bias and peak rotational and translational movements for the different groups in A. *p < 0.05 versus No Opsin mice. ^#p < 0.05 between optogenetic stimuli within a group.

Figure 12.

Optogenetic excitation of the superior colliculus biases contraversively spontaneous exploratory orienting movements. A, Each panel overlays the effects of trains (blue only) or continuous (blue or green) light on head bias (angle in degrees), and rotational and translational movement components (speed, cm/s) during exploration of an open field for the different groups used to excite the superior colliculus (noted in Fig. 7B). B, Population measures of peak head bias and peak rotational and translational movements for the different groups in A. *p < 0.05 versus No Opsin mice (shown in Fig. 11). ^#p < 0.05 between optogenetic stimuli within a group.