Calling song recognition in female crickets: temporal tuning of identified brain neurons matches behavior

Abstract

Phonotactic orientation of female crickets is tuned to the temporal pattern of the male calling song. We analyzed the phonotactic selectivity of female crickets to varying temporal features of calling song patterns and compared it with the auditory response properties of the ascending interneuron AN1 (herein referred to as TH1-AC1) and four newly identified local brain neurons. The neurites of all brain neurons formed a ring-like branching pattern in the anterior protocerebrum that overlapped with the axonal arborizations of TH1-AC1. All brain neurons responded phasically to the sound pulses of a species-specific chirp. The spike activity of TH1-AC1 and the local interneuron, B-LI2, copied different auditory patterns regardless of their temporal structure. Two other neurons, B-LI3 and B-LC3, matched the temporal selectivity of the phonotactic responses but also responded to some nonattractive patterns. Neuron B-LC3 linked the bilateral auditory areas in the protocerebrum. One local brain neuron, B-LI4, received inhibitory as well as excitatory synaptic inputs. Inhibition was particularly pronounced for nonattractive pulse patterns, reducing its spike activity. When tested with different temporal patterns, B-LI4 exhibited bandpass response properties; its different auditory response functions significantly matched the tuning of phonotaxis. Temporal selectivity was established already for the second of two sound pulses separated by one species-specific pulse interval. Temporal pattern recognition in the cricket brain occurs within the anterior protocerebrum at the first stage of auditory processing. It is crucially linked to a change in auditory responsiveness during pulse intervals and based on fast interactions of inhibition and excitation.

Figure 1.

Structure and location of auditory neurons in the cricket brain. A, Axonal projections of ascending neuron TH1-AC1 in the anterior protocerebrum. B, Morphology of B-LC3 with a cell body next to the optic nerve; dendritic arborizations overlap the ring-like arborization patterns of the ipsilateral TH1-AC1 and axonal projections overlap the contralateral one. C–E, Morphology of B-LI2, B-LI3, and B-LI4 with a lateral cell body.

Figure 2.

Activity of TH1-AC1 and phonotactic tuning of female crickets to different PD, PI, and PP. A, Top, Response of TH1-AC1 at PD-8, 20, and 40 ms. Bottom, Phonotactic (gray) and neural (black) PD-response functions. B, Top, TH1-AC1 responses at PI-5, 15, and 60 ms. Bottom, Phonotactic (gray) and neural (black) PI-response functions. C, Top, Response of TH1-AC1 at PP-18, 34, and 90 ms. Bottom, Phonotactic (gray) and neural (black) PP-response functions. The left scale indicates relative neural and phonotactic activity, and the right scale shows the absolute values of spike activity. Neural data are based on N = 9 females and n = 54 test sequences; phonotactic data are based on N = 10 (A, B) and N = 15 (C) animals. Error bars show SD of relative values.

Figure 3.

Activity of B-LI2, B-LC3, B-LI3, and B-LI4 and phonotactic tuning of females to different PD. Top, Response of neurons at PD-8, 20, and 40 ms. Bottom, Phonotactic (gray) and neural (black) PD-response functions. A, Activity and response function of B-LI2. Neural data are based on N = 2 females and n = 13 test sequences, 2 stainings. B, Activity and response function of B-LC3. Neural data are based on N = 5 females and n = 23 test sequences, 4 stainings. C, Activity and response function of B-LI3. Neural data are based on N = 5 females and n = 18 test sequences, 4 stainings. D, Activity and response function of B-LI4. Neural data are based on N = 3 females and n = 10 test sequences, 2 stainings. The left scale indicates relative neural and phonotactic activity, and the right scale shows the absolute values of spike activity. Error bars show SD of relative values.

Figure 4.

Activity of B-LI2, B-LC3, B-LI3, and B-LI4 and phonotactic tuning of females to different PI. Top, Response of neurons at PI-5, 15, and 60 ms. Bottom, Phonotactic (gray) and neural (black) PD-response functions. A, Activity and response function of B-LI2. Neural data are based on N = 2 females and n = 13 test sequences, 2 stainings. B, Activity and response function of B-LC3. Neural data are based on N = 5 females and n = 23 test sequences, 4 stainings. C, Activity and response function of B-LI3. Neural data are based on N = 5 females and n = 18 test sequences, 4 stainings. D, Activity and response function of B-LI4. Neural data are based on N = 3 females and n = 10 test sequences, 2 stainings. The left scale indicates relative neural and phonotactic activity, and the right scale shows the absolute values of spike activity. Error bars show SD of relative values.

Figure 5.

Activity of B-LI2, B-LC3, B-LI3, and B-LI4 and phonotactic tuning of females to different PP. Top, Response of neurons at PP-18, 34, and 90 ms. Bottom, Phonotactic (gray) and neural (black) PD-response functions. A, Activity and response function of B-LI2. Neural data are based on N = 2 females and n = 13 test sequences, 2 stainings. B, Activity and response function of B-LC3. Neural data are based on N = 5 females and n = 23 test sequences, 4 stainings. C, Activity and response function of B-LI3. Neural data are based on N = 5 females and n = 18 test sequences, 4 stainings. D, Activity and response function of B-LI4. Neural data are based on N = 3 females and n = 10 test sequences, 2 stainings. The left scale indicates relative neural and phonotactic activity, and the right scale shows the absolute values of spike activity. Error bars show SD of relative values.

Figure 6.

Relative responses of phonotaxis and brain neurons plotted against pulse duration (abscissa) and pulse interval (ordinate) based on all data points of the PD, PI, and PP test paradigms (e.g., data along the diagonal from the bottom left to the top right represent responses to the PP paradigm). In each plot, the x-axis starts at a pulse duration of 4 ms. Responses are color coded with red showing the area of maximum response, indicated by asterisks.

Figure 7.

Responses of TH1-AC1, B-LC3, and B-LI4 to different PI that were varied within a sequence of sound pulses or pairs of pulses; PD kept constant at 21 ms. A, Recording of TH1-AC1 (top) and PSTH (4 ms/bin) with averaged instantaneous spike frequency (bottom; N = 1 female, n = 40 sequences). B, Recording of B-LC3 (top) and PSTH (4 ms/bin) with averaged instantaneous spike frequency (bottom; N = 1 female, n = 10 sequences). C, Averaged synaptic activity of B-LI4 to single pulses (bottom) and pairs of sound pulses with PI ranging from 5 to 60 ms (N = 1 female, n = 16 for single pulses, and n = 4 for pairs of pulses).