Klinische Neurophysiologie 2013; 44 - P99
DOI: 10.1055/s-0033-1337240

Noise and Signal in the Human Brain

F Iliopoulos 1, T Nierhaus 1, A Villringer 1
  • 1MPI for Human Cognitive and Brain Sciences, Leipzig, Berlin, Deutschland

Background: It is well known that background noise interferes with sensory stimulation leading to the phenomenon of Stochastic Resonance (SR) {1, 2, 3}. SR predicts that the response of a nonlinear SR system to a weak input signal increases by the presence of a particular, nonzero level of noise. There is indication that SR related phenomena may occur both peripherally and in the central nervous system {4}. Cross modal SR developments further support that notion {5,6,7}. Here we investigate the behavioral SR effects of Electrical Noise Stimulation (ENS) on the perception of somatosensory stimuli in human subjects. Noise and detectable signal are of the same modality (direct current signals). The amount of noise was always mantained subliminal. We compare the likelihood of conscious perception during presence versus absence of different noise levels over three near threshold pulse intensities.

Methods/Results: Five psychophysical experiments are presented. In all five experiments, “test” signals consist of pulse nerve stimulation of the left index finger. Noise is applied intermittently in 20sec blocks. In exp 1 and 2, noise is delivered to the same finger, in exp 3 – 5 to the adjacent middle finger:

  • Detection of near-threshold pulses with and without noise at same finger. The Detection rate for near-threshold pulses of different intensities applied on the index finger is increased with additional noise; the effect is stronger for the two lowest pulse intensities.

  • Sinusoidal waveform vs. Single pulses. The Detection Rate (DR) for pulses of the lowest intensity increases with the addition of a sinusoidal signal while DR for pulses of the highest intensity evenly diminishes.

  • Noise vs. Single pulses. Presence of noise on the index or the adjacent finger decreases DR for pulses of the highest intensity.

  • Noise vs. Train pulses. Subjects improve the DR for the two lowest intensity train pulses with addition of noise on the index finger. Noise on the adjacent finger decreases detection of the highest train pulses.

  • Fast Noise vs. Long Single Pulses. Following the same paradigm, participants were subjected in a “yes” or “no” discrimination task of long (10 ms) pulse detection. D' values show that ample spectrum noise applied on the index finger significantly improves the ability of 9 out of 12 subjects to detect all 3 periliminal intensities of pulses.

Conclusion: In summary, we clearly confirm the presence of stochastic resonance effects in our model. These results provide a characteristic signature of SR and allow identifying a signal attribute set (time-amplitude parameters) for individual subjects that optimizes their performance.

References:

1. Douglass, J. K., L. Wilkens, E. Pantazelou, and F. Moss, 1993, Nature (London) 365, 337.

2. Levin JE, Miller JP (1996) Broadband neural encoding in the cricket cercal sensory system enhanced by stochastic resonance. Nature 380:165 – 168.

3. Bahar S, Neiman A, Wilkens LA, Moss F (2002) Phase synchronization and stochastic resonance effects in the crayfish caudal photoreceptor. Phys Rev E Stat Nonlin Soft Matter Phys 65:050901.

4. Manjarez et al., The Journal of Neuroscience, 15 March 2003, 23(6): 1997 – 2001

5. Ward LM, Desai S, Rootman D, Tata MS, Moss F. Noise can help as well as hinder seeing and hearing. Bull Am Phys Soc 2001; 46:N23.002.

6. Zeng F-G, Fu Q-J, Morse R. Human hearing enhanced by noise. Brain Res Interact 2000; 869:251 – 5.

7. Kitajo K, Nozaki D, Ward LM, Yamamoto Y. Behavioral stochastic resonance within the human brain. Phys Rev Lett 2003; 90:218103.