Fast and slow transitions in frontal ensemble activity during flexible sensorimotor behavior

Abstract

The ability to shift between repetitive and goal-directed actions is a hallmark of cognitive control. Previous studies have reported that adaptive shifts in behavior are accompanied by changes of neural activity in frontal cortex. However, neural and behavioral adaptations can occur at multiple time scales, and their relationship remains poorly defined. Here we developed an adaptive sensorimotor decision-making task for head-fixed mice, requiring them to shift flexibly between multiple auditory-motor mappings. Two-photon calcium imaging of secondary motor cortex (M2) revealed different ensemble activity states for each mapping. When adapting to a conditional mapping, transitions in ensemble activity were abrupt and occurred before the recovery of behavioral performance. By contrast, gradual and delayed transitions accompanied shifts toward repetitive responding. These results demonstrate distinct ensemble signatures associated with the start versus end of sensory-guided behavior and suggest that M2 leads in engaging goal-directed response strategies that require sensorimotor associations.

Figure 1. Behavioral performance of head-fixed mice in an adaptive sensorimotor decision-making task

(a) Schematic of experiment. Each trial begins with an auditory cue. A response window starts 0.5 s after cue onset, during which the first lick is recorded as the response for that trial. Water reward is delivered contingent on a correct response. (b) There are three trial types, which vary by their cue-response mappings. In sound-guided trials, the correct response is left for the upsweep sound (5-to-15 kHz frequency-modulated) and right for the downsweep sound (15-to-5 kHz). For action-guided left and right trials, the correct responses are left and right, respectively, for either sound cue. Trials of the same type are presented in blocks. Block switches, in which a new trial type is introduced, occur when the correct rate reaches 85% for the last 20 trials. (c) Behavioral performance surrounding a block switch, either from action to sound (top) or sound to action (bottom). Filled circle, hit rate. Open circle, perseverative error rate. Dotted line, other error rate. Mean±s.e.m. of 33 action to sound switches and 38 sound to action switches. (d) Performance from one example behavioral session. Each trial results in 1 of 4 outcomes: correct (filled circle), perseverative error (open circle), other error (open triangle), or miss (cross). Vertical line, block switch. (e) Lick rates detected at the left and right lick ports for upsweep or downsweep sound cues during all correct sound-guided (black), action-left (red), and action-right (blue) trials. For each choice direction, lick rates in action trials were compared with those in sound trials in 0.1 s bins, and the bars atop the panels denote significant differences (p<0.01, paired t-test). Line, mean. Shading, ±s.e.m. n = 9 sessions from 5 mice.

Figure 2. Bilateral inactivation of secondary motor cortex impairs adjustment to sound-guided trials

(a) Schematic of experiment. (b) Task performance after bilateral infusion of saline vehicle (Veh) or muscimol (Mus) into M2 (c) Effects of muscimol infusion on action-to-sound and sound-to-action block shifts. Gray lines, individual paired experiments. Bar, mean±s.e.m. Wilcoxon signed-rank test. n = 11 mice.

Figure 3. Two-photon calcium imaging of task-related activity in secondary motor cortex

(a) Example post hoc and (b) in vivo two-photon images of GCaMP6s-expressing neurons in layer 2/3 of M2. (c) Fractional fluorescence changes (ΔF/F) in example M2 neurons during performance of sound-guided trials. Vertical line indicates the time of response associated with correct left (solid black), correct right (dotted black), or incorrect (magenta) trials. (d) Trial-averaged ΔF/F of four M2 neurons for correct left (solid line) and correct right (dotted line) responses in sound-guided (black) and action-guided (red) trials. Line, mean. Gray shading, 95% confidence intervals.

Figure 4. Transitions in ensemble activity occur earlier and are more abrupt following switch to sound-guided trials

(a) A schematic illustrating ensemble activity dynamics around a block switch. Each curved line represents a single-trial neural trajectory deduced from calcium imaging data. When the contingencies switch, neural trajectories move within the representational space. Trial-by-trial location of ensemble activity patterns was determined by calculating a ratio of Mahalanobis distances, d_origin/(d_origin + d_dest), where d_origin and d_dest are the Mahalanobis distance from neural trajectory in the current trial to those of the 20 trials pre-switch for the last and current blocks, respectively. (b) Trial-by-trial location of ensemble activity patterns surrounding two switches from action to sound block. Trial outcomes are plotted on the top row: correct (filled circle), perseverative error (open circle), and other error (open triangle). Filled circles, Mahalanobis distance ratios for individual trials. Line, fit to the logistic function. Upward arrow, behavioral transition trial. Downward arrow, neural transition trial. (c) Same as (b) for two switches from sound to action block. Note the vertical axis is inverted for presentation purposes. (d) Summary of parameters extracted by fitting action-to-sound neural transitions with the logistic function. Arrow, median value. (e) Neural transition trials plotted against behavioral transition trials for action-to-sound switches (see Methods for definition of transition trials). Each symbol represents one block switch. Symbol shapes denote the different sessions. Large circle, median value. (f) Mean hit and error rates at the behavioral trial corresponding to specific neural transition locations as estimated by the logistic fit for each action-to-sound transition. Circles, mean±s.e.m. (g–i) Same as (d–f) for switches from sound to action block; black arrows in (f) shown for comparison with (c). *, p<0.05; **, p<0.01, Wilcoxon rank-sum test. Difference in range, L, was not significant (sound: 0.36, action: 0.38, median; p = 0.8, z = 0.28, Wilcoxon rank-sum test). Rightmost bar of the histogram includes all instances above the range. n = 33 action-to-sound and 35 sound-to-action switches from 9 sessions from 5 mice.

Figure 5. Multiple strategies are associated with distinct population activity patterns

(a) Neuronal circuit trajectories for an ensemble of 56 simultaneously imaged cells in one experiment. Trajectories were determined from trial-averaged ΔF/F for 44 correct left (dotted line) and 59 correct right (solid line) responses in sound-guided trials. Open circle, time of response. Filled circles, 3 and 6 s after response. PC, principal component. (b) Same axes as (a), with additional trajectories from 51 correct action-left (red) and 51 correct action-right (blue) trials. Left, trajectories calculated using trial-averaged ΔF/F. Right, three representative single-trial trajectories from each trial type. (c) Median accuracy of decoding trial type from individual population activity vectors. S, sound; AL, action-left; AR, action-right. Open triangles, individual experiments. Filled triangles, mean±s.e.m. Dotted line, chance-level accuracy. (d) Temporal dependence of ensemble decoding accuracy, calculated by repeating the decoding analysis separately for each 0.28-s-long window with step size of 0.28 s. The window duration is the inverse of imaging frame rate, which is 3.6 Hz. Gray, individual experiments. Black, mean. Dotted line, chance-level accuracy. (e) Median accuracy of decoding trial type from fluorescence transients of single neurons. Green circles, trial type-selective cells, i.e. 95% percentile confidence intervals are above chance-level of 33.3%. Black circles, other cells. Black line, mean decoding accuracy using ensemble activity. Dotted line, chance-level accuracy. (f–g) Same as (b–c) except restricting to trials matching these conditions: stimulus was upsweep, choice was left, and outcome was reward for the current trial, and choice was left for the prior trial. Trial type could be decoded well above chance (sound: 87±5%, action-left: 88±5%; versus chance level of 50%, p = 7 x 10⁻⁵, 7 x 10⁻⁵, t(8) = 7.50, 7.52, one-sample t-test). (h–i) Same as (b–c) except restricting to trials matching these conditions: stimulus was downsweep, choice was right, and outcome was reward for the current trial, and choice was right for the prior trial. Trial type could be decoded well above chance (sound: 85±5%, action-right: 86±4%; versus chance level of 50%, p = 7 x 10⁻⁵, 8 x 10⁻⁶, t(8) = 7.54, 10.01, one-sample t-test). n = 9 sessions from 5 mice.

Figure 6. M2 ensembles revisit previous activity patterns upon re-exposure to corresponding trial-type

(a) Neural circuit trajectories, calculated from trial-averaged ΔF/F for each trial block during one behavioral session. Circled numbers denote temporal order in which trial blocks were presented. Open circles, time of response. Black, sound-guided. Blue, action-right. Red, action-left. (b) Normalized distance between neural circuit trajectories from different trial types across all experiments (see Methods) for sound (S), action-left (AL), and action-right (AR). Open triangles, median distances from individual experiments. Solid triangles, mean±s.e.m. **, p<0.01, Wilcoxon rank-sum test, corrected α = 0.01. n = 9 sessions except for AL-AL (n = 4) and AR-AR (n = 8) because mice did not perform enough switches to experience the same block type again in some sessions. n = 9 sessions from 5 mice.

Figure 7. Comparison between neural activity patterns in M2, ALM, and V1 during flexible sensorimotor behavior

(a) Multiple linear regression analysis was used to evaluate the fraction of 562 M2 neurons encoding choice signals as a function of time. Regression was performed with a moving window (duration = 0.5 s, step = 0.5 s) to test for significance with α = 0.01 on all sound-guided trials where the current and prior outcomes are hits (i.e. R(n) = 1 and R(n-1) = 1). The bars atop the panels denote significant fractions (p<0.01, binomial test). Gray shading, significance level of 0.01. Dotted line in the middle panel, fraction of cells significant for the interaction term C(n)*C(n-1). n = 9 sessions from 5 mice. (b) Same as (a) for 518 ALM neurons. n = 8 sessions from 4 mice. (c) Same as (a) for 227 V1 neurons. n = 4 sessions from 2 mice. (d) Median accuracy of decoding trial type from individual population activity vectors restricted to matched trials, comparing M2, ALM, and V1 ensembles. For the S:AL subset, sound and action-left trial types were decoded from trials where stimulus was upsweep, choice was left, and outcome was reward for the current trial, and choice was left for the prior trial. For the S:AR subset, sound and action-right trial types were decoded from trials where stimulus was downsweep, choice was right, and outcome was reward for the current trial, and choice was right for the prior trial. Trial type decoded with high accuracy using ensemble activity from M2 (matched sound: action-left trials: 84±4%, t(8)=8.37; p=3 x 10⁻⁵; matched sound: action-right trials: 81±2%, t(8)=12.73; p=1 x 10⁻⁶; versus chance level of 50%, one-sample t-test). Open triangles, individual experiments. Filled triangles, mean±s.e.m. Dotted line, chance-level accuracy. (e) Neural transition parameters obtained by fitting action-to-sound (black) and sound-to-action (red) transitions with the logistic function, comparing M2 and ALM ensembles. Difference in L for ALM was not significant (sound: 0.35, action: 0.31, median; p = 0.51, z = −0.65, Wilcoxon rank-sum test). Filled circle, median. Line, 25^th and 75^th percentiles. *, p<0.05; **, p<0.01, Wilcoxon rank-sum test.