Fig 1.
Overview of the wireless telemetry system.
A: Wireless telemetry transmitter (Tosaka) that was designed to be attached to the head of a rat. It was 2.6 cm in length, 1.0 cm in width, and 1.9 cm in height, and it weighed 6.0 g. Transmitter range was approximately 10 m. A commercially available lithium coin cell battery (CR2032) was inserted into the Tosaka. Battery life was approximately 12 h. B: Drawing showing a Tosaka on the head of a rat (viewed from the right side). A Tosaka was attached into a U-shaped plate with plastic screws. A flexible electric wire was plugged into the Tosaka and IC pins that were connected to the recording electrodes. C: Drawing showing a block of dental acrylic cemented to the skull before attaching the Tosaka shown in (B). D: Drawing showing a Tosaka on the head of a rat (viewed from behind). CB: circuit board. E: Drawing showing a block of dental acrylic cemented to the skull before attaching the Tosaka shown in (D). F: System diagram of the transmitter and receiver. A neural signal was inputted into the input connector of a Tosaka, amplified with a gain of 1000, band-pass filtered (100–3000 Hz) with 3 pole band-pass filters, and modulated with a central frequency of 7.5 kHz by a voltage-controlled oscillator (sub-modulator). The signal was finally converted to a radio-frequency signal with a central frequency of 315, 433, or 565 MHz (main carrier frequency) by an RF modulator (main-modulator), and transmitted via an antenna. The radio frequency signal was received by 4 dipole antennas that were attached to the outside surface of a test box, demodulated by a main-demodulator, and then re-demodulated by a sub-demodulator. The signal was band-pass filtered (100–3000 Hz) and sent to a data acquisition system. G: Photograph of a rat equipped with a Tosaka. The Tosaka looks like a crest. A Tosaka with a flexible electric wire was usually wrapped with surgical tape for protection during the social interaction test. H, I: Neural activity was recorded from the PL in an anesthetized rat using a conventional tethered system (H) and the wireless telemetry system (I) simultaneously, in order to assess the wireless telemetry system. Comparison of the signals indicated that the signals obtained using the wireless telemetry system were comparable in quality to those acquired using the tethered recording system. Some differences were observed in spike waveforms and noise levels, which are thought to be mainly a result of differences in filtering and sampling.
Fig 2.
Wireless recording of multiunit activity in a freely moving rat.
A: Raw neural activity recorded from the IL during the social interaction test. B: Close up view of the neural activity enclosed by a rectangle in (A). Multiunit activities with various amplitudes are observed. C: Multiunit activities extracted from the raw neural activity in (A). Multiunit activities with various amplitudes show similar waveforms, which suggests that all of the neurons recorded are the same type.
Fig 3.
Examples showing the behavior of the rats during the social interaction test.
A Tosaka was attached to each animal’s head. The back of one of the pair was marked with black spray. The pair of rats was placed in a test box located in a darkened room. A, B: Sole behavior. Rats are behaving separately. The rat (no mark on its back) is exploring around by itself at the lower left corner of the test box and the partner (a black mark on its back) is resting at the lower right corner (A). Both rats are walking along the wall (B). C, D: Approaching behavior. The rat (arrow) is approaching the partner (C), and the partner (arrow) is approaching the rat (D). E–G: Contact behavior. Rats are sniffing (E) and boxing (F) each other, and the rat (arrow) is pinning and biting the partner (G). H, I: Leaving behavior. The rat (arrow) is leaving the partner (H), and the partner (arrow) is leaving the rat (I).
Table 1.
Duration and frequency of behaviors of group-reared rats (n = 32) during the 15-min social interaction test.
Fig 4.
Photomicrographs showing the position of the recording sites.
A, B: Arrows indicate the mark of the tip of a recording electrode in the PL (A) and IL (B). The tip of the recording electrode is identified with a blue spot of deposited iron. Outlines of the PL and IL are indicated with solid and dashed lines. Scale bars = 0.5 mm.
Fig 5.
Histograms illustrating multiunit activity of PL and IL neurons during the social interaction test.
A: Multiunit activity recorded in the PL. The blue, red, orange, and green columns represent firing rate during sole, approaching, contact, and leaving behavior, respectively. The firing rate increases during approaching (red columns) and contact (orange columns) behavior. The arrowheads indicate some of the instances when increased firing rates were observed during approaching behavior. Mean firing rates during sole, approaching, contact, and leaving behavior in this rat were 6.5 Hz, 9.0 Hz, 7.5 Hz, and 6.4 Hz, respectively. B: Multiunit activity recorded in the IL. The blue, red, orange, and green columns represent firing rate during sole, approaching, contact, and leaving behavior, respectively. The firing rate increases during leaving behavior (green columns). The arrowheads indicate some of the instances when increased firing rates were observed during leaving behavior. Mean firing rates during sole, approaching, contact, and leaving behavior in this rat were 5.0 Hz, 3.4 Hz, 4.9 Hz, and 6.4 Hz, respectively. The histogram bin size is 1 s. The gray columns indicate that multiunit activity was not discriminated from the artificial noise generated by sharp head shaking and self-grooming. When more than 2 behaviors were observed in a period of 1 column, the color of the behavior observed for the longest time is applied to the column.
Fig 6.
Firing rate of PL and IL neurons in the social interaction test.
A, B: Mean firing rates of PL neurons (n = 15) (A) and IL neurons (n = 12) (B) during sole (blue columns), approaching (red columns), contact (orange columns), and leaving (green columns) behavior. The firing rates of PL neurons during approaching and contact behavior were significantly higher than during sole and leaving behavior (A). The firing rate of IL neurons during leaving behavior was significantly higher than during sole, approaching, and contact behavior (B). Data represent means ± SEM. *P < 0.05, **P < 0.01; one-way repeated measures ANOVA with Bonferroni post hoc test.
Fig 7.
Firing rate of PL and IL neurons during sole, approaching, contact, and leaving behavior.
A, B: The firing rate of PL (A) and IL (B) neurons during sole behavior. Sole behavior was classed into non-walking (white columns) and walking (black columns) behavior. There were no significant differences between the firing rates during non-walking and walking behavior. C, D: The firing rate of PL (C) and IL (D) neurons during approaching behavior. Approaching behavior was classed into “the rat approaching the partner” (white columns) and “the partner approaching the rat” (black columns). There were no significant differences between the firing rates when the rat approached the partner and when the partner approached the rat. E, F: The firing rate of PL (E) and IL (F) neurons during contact behavior. Contact behavior was classified into 3 groups: socially exploring (gray columns), aggressive (white columns), and defensive (black columns). The firing rate during aggressive behavior was significantly higher than during socially exploring and defensive behavior in PL neurons (E), whereas no significant change in firing rate was observed in IL neurons (F). G, H: The firing rate of PL (G) and IL (H) neurons during leaving behavior. Leaving behavior was classed into “the rat leaving the partner” (white columns) and “the partner leaving the rat” (black columns). There was no significant difference between the firing rates of PL neurons when the rat left the partner and when the partner left the rat (G). The firing rate of IL neurons when the partner left the rat was significantly higher than when the rat left the partner (H). Data represent means ± SEM. *P < 0.05, **P < 0.01.
Table 2.
Duration and frequency of the behaviors of isolation-reared rats (n = 32) during the 15-min social interaction test.
Fig 8.
Histograms illustrating multiunit activity of PL and IL neurons of isolation-reared rats during the social interaction test.
A: Multiunit activity recorded in the PL. The blue, red, orange, and green columns represent firing rate during sole, approaching, contact, and leaving behavior, respectively. The firing rate increases during approaching (red columns) behavior. The arrowheads indicate some of the instances when increased firing rates were observed during approaching behavior. The firing rate appears to increase during contact (orange columns) behavior. Mean firing rates during sole, approaching, contact, and leaving behavior in this rat were 5.1 Hz, 6.9 Hz, 6.3 Hz, and 4.4 Hz, respectively. B: Multiunit activity recorded in the IL. The blue, red, orange, and green columns represent firing rate during sole, approaching, contact, and leaving behavior, respectively. Mean firing rates during sole, approaching, contact, and leaving behavior in this rat were 7.5 Hz, 5.8 Hz, 5.6 Hz, and 6.6 Hz, respectively. The histogram bin size is 1 s. The gray columns indicate that multiunit activity was not discriminated from the artificial noise generated by sharp head shaking and self-grooming. When more than 2 behaviors were observed in a period of 1 column, the color of the behavior observed for the longest time is applied to the column.
Fig 9.
Firing rate of PL and IL neurons of isolation-reared rats in the social interaction test.
A, B: Mean firing rates of PL neurons (n = 14) (A) and IL neurons (n = 12) (B) during sole (blue columns), approaching (red columns), contact (orange columns), and leaving (green columns) behavior. The firing rates of PL neurons during approaching and contact behavior were significantly higher than during sole and leaving behavior (A). No significant changes in the firing rate of IL neurons were observed during the 4 behaviors (B). Data represent means ± SEM. *P < 0.05, **P < 0.01; one-way repeated measures ANOVA with Bonferroni post hoc test.
Fig 10.
Firing rate of PL and IL neurons of isolation-reared rats during sole, approaching, contact, and leaving behavior.
A, B: The firing rate of PL (A) and IL (B) neurons during sole behavior. Sole behavior was classed into non-walking (white columns) and walking (black columns) behavior. There were no significant differences between the firing rates during non-walking and walking behavior. C, D: The firing rate of PL (C) and IL (D) neurons during approaching behavior. Approaching behavior was classed into “the rat approaching the partner” (white columns) and “the partner approaching the rat” (black columns). There were no significant differences between the firing rates when the rat approached the partner and when the partner approached the rat. E, F: The firing rate of PL (E) and IL (F) neurons during contact behavior. Contact behavior was classified into 3 groups: socially exploring (gray columns), aggressive (white columns), and defensive (black columns). There were no statistical significant differences among these firing rates. G, H: The firing rate of PL (G) and IL (H) neurons during leaving behavior. Leaving behavior was classed into “the rat leaving the partner” (white columns) and “the partner leaving the rat” (black columns). There were no significant differences between the firing rates when the rat left the partner and when the partner left the rat. Data represent means ± SEM.