Comunicação serial assíncrona com o cérebro: padrões temporais de microestimulação elétrica ditando o comportamento

Abstract

Electrical microstimulation (ES) of primary sensory areas has shown some promising results on imputing information to the brain. In quite general terms, the modal perception is based on the area electrodes are placed, while the intensity of perception is driven by the ES frequency pattern. One unexplored possibility is that a single electrode delivering temporally coded stimuli, mimicking an asynchronous serial communication port to the brain, can trigger the emergence of different brain-states. Thus, this work tests the hypothesis if whether a specific polymodal associative area (the amygdaloid complex) may distinguish between two different temporally organized sequences of ES. In other words, if two binary sequences (same number of 0s and 1s bits), are used to control a ES device connected to the AMY, would it be possible to associate different qualia of perception to each binary sequence? Wistar rats (250 310 g) were submitted to a surgical implant of ES electrodes in the amygdala basolateral complex. Animals then underwent a classical conditioning paradigm, which consisted of pairing distinct patterns of ES (conditioned stimuli - biphasic square waves, 25 A, 100 s) to an unconditioned stimulus (footshock, 0.4 mA, during 2 s). The acquisition of conditioned behavior was evaluated by measuring the freezing (no movements - except breathing - for 3 s). In the first protocol we used a periodic pattern of 6 Hz ES (166.7 ms inter pulse interval - IPI) as conditioned stimulus. The freezing response was significantly higher in the paired group (69 ± 5%) when compared to the unpaired group (25 ± 8%, p < 0.001). In the second protocol, we used two distinct temporal patterns of ES, both with six pulses per second: (A) 1110000111 and (B) 1001111001, with bits separated by a 10ms IPI. During the conditioning phase, all animals were stimulated as: 1) A-paired and B-unpaired; 2) A-unpaired and B-paired and 3) A-unpaired and B-unpaired. Conditioned behavior was evaluated for 3 consecutive days using only one ES pattern per day; respectively, pattern B A B. A proper conditioned response was observed, in Day 1, only for the B-paired group (B-paired: 49 ± 7%; A-paired: 22 ± 5%, p < 0.05; Unpaired: 13 ± 4%, p < 0.001). In Day 2, only the A-paired group showed significant freezing (B-paired: 10 ± 2%; A-paired: 49 ± 12%, p < 0.001; Unpaired: 8 ± 2%, p < 0.001). In Day 3 results were similar to Day 1 (B-paired: 42 ± 8%; A-paired: 27 ± 10%, p=ns; Unpaired: 14 ± 3%, p < 0.01). In order to determine the neural substrates recruited by the different stimulation patterns, c-Fos expression was evaluated one and a half hours after the last retention test. Animals conditioned to word-B, after stimulation with word-B, demonstrated increased hypothalamic c-Fos staining. Animals conditioned to word-A, however, showed increased prefrontal c-Fos labeling. In addition, prefrontal-cortex and hypothalamic c-Fos staining for, respectively, word-B and word-A conditioned animals, was no different than that of an unpaired control group. Our results suggest that, depending on the valence acquired from previous learning, temporally coded microstimulation activates distinct neural networks and associated behavior.