Biologically Inspired Intelligent Systems

1. Biologically Inspired Intelligent Systems Lecture 7 Dr. Roger S. Gaborski

2. Different Regions of the Cortex • Different regions of the cortex have different functions  • The parietal lobe along the central sulcus is the primary somatic sensory cortex (S1).  Sensory signals from the body surface are mapped to it. • Four distinct regions. Known as Brodmann’s areas:3a, 3b, 1 and 2

4. The Somatic Sensory Cortex Motor & Sensory Cortex: http://predator.pnb.uconn.edu/beta/virtualtemp/nervous/Motor_and_Sensory_Cortexes.htm

5. The Somatic Sensory Cortex • The somatic sensory cortex strip is the part of the brain that receives input from receptors in the body. • It mediates our sense of touch • Different zones of somatosensory cortex are activated by stimulation of different sites on the skin

6. The Somatic Sensory Cortex • Cortical columns in somatosensory cortex respond to specific modalities: • Touch • Temperature • Pain

7. Somatotopic Map of the Body's Surface Cartoon Map: http://predator.pnb.uconn.edu/beta/virtualtemp/nervous/the_Homoculous.htm

8. Brain Mapping Somatotopic Map: http://predator.pnb.uconn.edu/beta/virtualtemp/nervous/Somatotopic%20Map.htm

9. The Somatic Sensory Cortex Motor & Sensory Cortex: http://predator.pnb.uconn.edu/beta/virtualtemp/nervous/Motor_and_Sensory_Cortexes.htm

11. Whiskers • Principal source of sensory information in rodents • QUESTION- how does neural activity represent the objects a rodent interacts with? • In the visual system photoreceptors transduce energy of photons • Rodents move their whiskers at a rate of 5-12 Hz • Mechanical properties of whiskers transduce contact information

12. Rat Whiskers • Whiskers in rats have been recognized as an important source of sensory input. • Used for object localization • Used for determining roughness and texture of surfaces • Used for detecting sizes and shapes of small objects • This sensory input probably developed to compensate for poor vision

13. Rat Whiskers • Rats can extend whiskers as far as two inches in front of them in order to sense objects • When the rat whisks an object, signals travel from the receptor cells in the whisker follicle to the trigeminal brainstem complex, and then to the thalamus and the primary somatosensory cortex

14. Whiskers are the interface between external objects and the sensory receptor neurons • Discriminative capacity exceeds those of humans using their fingertips

15. Rat WhiskersAn Active Process • Rat whisker system is an active process • The rat sweeps its whiskers through the air seeking out things • There is continuous determination of identifying objects • Each whisker follicle contains a bundle of 200-300 sensory fibers

16. Rat Whiskers The Path to the Brain • Sensory signals travel along the afferent nerve to the brain to the first synapse and through the axons to the thalamic somatosensory nuclei

17. Spatial Arrangement and Barrels • Somatosensory (SI) cortex in rats characterized by clustering of Layer IV neurons known as Barrels • Single Barrel represents structural unit - corresponds to a single whisker • Whisker that corresponds most directly w/ neuron is the Principal Whisker (PW) • Surround Whiskers (SW) correspond to a weaker neuron firing rate • Thus, the rodent pathway is a great model for studying spatial and temporal properties of cortical neurons

18. Spatial Arrangement and Barrels • The spatial arrangement of the whiskers on the rat’s face is one of a matrix of large hairs (5 rows x 5-9 columns) which is represented in these brain areas by a topographically similar matrix of cell rings. • The aggregates of cell rings in layer IV of the cerebral cortex are referred to as barrels. • Termed barrel cortex because the neurons are grouped in barrel-like arrangements, with a hollow center of lesser cell density surrounded by a circle of higher cell density, and because they appear as a stack of barrels when viewed from one end Source: Nackley, Andy: http://www.arches.uga.edu/~anackley/thesis2.htm

19. The Somatic Sensory Cortex • What is interesting about rats and their whisker sensory system? • The whisker sensory system is efficient and highly evolved • By modeling the whisker sensory system in rats it can be possible to model other systems like the human visual system • It was discovered in 1970 by Woolsey and Van der Loos that there is a one-to-one mapping between sensory receptors in rat whiskers to the brain in a columnar pattern

20. The Question • Is the signal from one whisker processed in a single columnar module or does a large set of columns process a single whisker? • Can one column support a meaningful behavior? • Is there such thing as single-whisker learning?

21. The Experiment Figure From: "Investigations into the organization of information in sensory cortex,"  Diamond M.E., Petersen R.S., Harris J.A., and Panzeri S

22. The Experiment • Train the barrel cortex • Clip all but one whisker off of the base of one side of the face - no whiskers on other side as well • Use dim red light so rat is forced to rely on single whisker to maneuver • Let rat use whisker to detect opposite platform before jumping across to obtain chocolate reward

23. The Experiment – The Training • Over time, extend gap • Vary platform position and occasionally remove platform

24. The Next Step • After one week of training, the single whisker is clipped and a “prosthetic” whisker is attached to the previously trained whisker stub using superglue • Other rats had prosthetic whisker placed in surrounding rows and columns of trained whisker • Other rats had prosthetic whisker placed on other side of face

25. The Experiment – Results • Rats appeared to use single whisker to confirm platform existence and identity (ex: size, angle, height) • When prosthetic whisker attached to immediate surrounding trained whisker, learning was much faster. Much slower when attached farther away

26. The Experiment - Results • Rats could rapidly transfer learning to whiskers symmetrically opposite the trained whisker, but more training was required for different rows and much more learning was required beyond that • Therefore, somatosensory cortex show signs of transfer of learning

27. Conclusion • Neural modifications in barrel cortex appear to be localized in columns • The behavior transfer of previous learning engages new cortical columns and the closer the sets are the more likely that little to no relearning is required

28. Experiments • Have shown that the majority of neurons had large (~4 - 13 whiskers) receptive fields for touch • Rat primary somatosensory cortex does not operate as static decoder of tactile info • Instead - tactile processing involves on-going interactions between neuron bundles • (ref: Ghazanfar, Nicolelis, “Spatiotemporal Properties of Layer V Neurons of the Rat Primary Somatosensory Cortex.” 1999).

29. Animals able to readily perceive and differentiate among signals to guide behavior • Suggests a nervous system capable of processing complex, time-dependent signals in “real-time”

30. Model Animal • It would be useful to be able to model this behavior - take in many signals, analyze time-dependent data efficiently

31. More about the rats • As previously stated, Rats employ whisker movements while exploring • It has been proposed that the time-dependent nature of RF in the rat thalamus reflects this active sensory processing (Nicolelis and Chapin, 1994) • When rats are prevented from using their whiskers actively - ability to explore is reduced (Carvell and Simons, 1996)

32. Next ExperimentDetermine Receptive Field Size • Craniotomy - part of the rat’s skull removed to access the brain • Microarray implanted in rat’s SI cortex to monitor spike activity

33. Results • The receptive field size of a neuron was assessed by counting # of whiskers that could elicit a response • ~ 4 - 13 whiskers corresponded to one Receptive Field • Some neurons responded to only ONE or TWO whiskers, while other neurons responded to nearly all whiskers

34. In Another Experiment • Hypothesized that cortical barrel non-principle whiskers produce a net inhibitory effect • Selected whiskers were cut • Absence of whiskers surrounding PW lead to 20% increase in cortical activity and 37% decrease in thalamic activity

35. Same Experiment • Removal of the PW resulted in 50% decrease in cortical neurons firing • What does this mean? • Consistent w/ idea that each barrel uses multiple whisker thalamic input and lateral inhibition to sharpen RF • (Kelly, Carvell, et al. - “Sensory Loss by Selected Whisker Removal Produces Immediate Disinhibition in the Somatosensory Cortex of Behaving Rats”, 1999.)

36. Other Results • Whisker trimming in neonatal animals leads to permanent abnormalities in cortex, cortical RF properties and whisker-based environmental exploration • In adult animals, alterations in cortical RFs are made within days of whisker removal

37. Whisker Model- Peter Konig • Simulation using artificial whiskers • Steel wire mounted to a servo mechanism that can sweep back and forth • Swept at 1Hz • At base of whisker a magnetic field sensor measured distortion to the magnetic field caused by the whisker movement

38. Experiments • Record whisker movement on 8 different types of sandpaper • Whisker movement characterized by power spectrum • The resulting power spectrum could be used to classify the different textures.

39. Israeli universities part of 'rodent whiskers' robotic projectFeb 10, 2008 21:28 | Updated Feb 10, 2008 22:20 Taking a lesson from mice and rats, which find their way in the dark with their whiskers, a multinational team that includes Israelis is developing innovative touch technologies, including a robot that will be able to quickly locate, identify and capture moving objects in space. The BIOTACT nature-imitation project, funded primarily by the EC Seventh Research Framework Program, includes participation by scientists from universities, research institutes and high-tech companies in Israel, Britain, Switzerland, Italy, France, Germany and the US. Based on principles of active sensing adopted widely in the animal kingdom, the multinational team plans to produce the "whiskered" robotic rat. "The use of touch in the design of artificial intelligence systems has been largely overlooked until now," says participant Prof. Ehud Ahissar of the neurobiology department at Rehovot's Weizmann Institute of Science.

40. EXAM 1 • General brain anatomy • MODELS: • Action Potential model • Neuron models: perfect integrator model and leaky integrator model • Hebb Learning • Spiking Neuron (“Spike-based strategies for rapid processing,” Simon J. Thorpe, Arnaud Delorme & Rufin VanRullen • Visual System (lectures 8 and 9) • Dorsal pathway & Ventral Pathway • Receptive fields