Minds brains and machines Part II Josep M. Sopena
Course Evaluation • Exam (to be decided). • In this part of the course, I will give you some home or class exercises which I can use to evaluate you. • You should also read two papers which I will put on the course web site. The papers will be on the web site tomorrow.
Preliminaries Joshua Greene and Jonathan Cohen (2004) For the law, neuroscience changes nothing and everything
Is there something wrong with this text? • “When a composer conceives a symphony, the only way he or she can present it to the public is through an orchestra. . . If the performance is poor, the fault could lie with the composer’s conception, or the orchestra, or both. . . Will is expressed by the brain. Violence can be the result of volition only, but if a brain is damaged, brain failure must be at least partly to blame”. (Pincus 2001, p. 128) Tema 7
To our untutored intuitions, this is a perfectly sensible analogy, but it is ultimately grounded in a kind of dualism that is scientifically untenable. It is not as if there is you, the composer, and then your brain, the orchestra. You are your brain, and your brain is the composer and the orchestra all rolled together. Tema 7
And is this other text? • Most of the developmental research on cognitive and psychosocial functioning in adolescence measures behaviors, selfperceptions, or attitudes, but mounting evidence suggests that at least some of the differences between adults and adolescents have neuropsychological and neurobiological underpinnings. (Steinberg & Scott 2003, p. 5) Tema 7
Criticism • Some of the differences? Unless some form of dualism is correct, every mental difference and every difference in behavioural tendency is a function of some kind of difference in the brain. But here it is implicitly suggested that things like ‘behaviours, self-perceptions, or attitudes’ may be grounded in something other than the brain. Tema 7
Mind, brain and behavior • Dualism is scientifically untenable. • The mind is what the brain does. • All behavior is a product of brain activity.
Common sense is not a good source of evidence • Our common sense tell us that our will governs our behavior an it is uncaused, but … • Common sense is nothing more than a deposit of prejudices laid down by the mind before you reach eighteen (Einstein)
Common sense • “None of us enjoys the thought that what we do depends on processes we do not know; we prefer to attribute our choices to volition, will, or self-control. . . . Perhaps it would be more honest to say, ‘My decision was determined by internal forces I do not understand’” (Marvin Minsky 1985; 306).
Computational Neuroscience A brief intoduction
The questions • How the brain controls behavior? • How the brain makes emotions? • How intelligence emerges from neural activity? • …… Tema 7
Computational Neuroscience • To answer these and other related questions is the main goal of Computational Neuroscience. • It relies on mathematical modeling approaches to understand the function of the nervous system and to design systems that duplicate/simulate behaviors.
Classes of brain models(first approximation) • Realistic brain models (more descriptive). • Simplified brain models (more explicative).
Realistic models(Sejnowsky et al. 1988) • Realistic brain models try to incorporate as much of the cellular detail as is available.
Realistic brain models(are they adequate?) • Lets suppose we are observing the neuron number 12345789 (we have 1011 neurons and 1016 connections) and find out that: The neuron is resting, and, as usual, there is a higher concentration of potassium ions inside the cell than outside (namely a concentration g ions/mm), and a higher concentration (l) of sodium ions outside than inside. Within the neuronal membrane are gated sodium and potassium channels, each specific to either sodium or potassium, respectively. In response to a stimulus, both of these channels open, in which case there is an influx of sodium ions down their concentration gradient and an outflux of potassium ions down their concentration gradient. The effect of the influx of sodium ions is to increase the membrane voltage (Vm) and the effect of the outflux of potassium ions is to decrease the membrane voltage….
Exercise • Is this all that we need to answer the questions above? • How the brain controls behavior? • How the brain makes emotions? • How intelligence emerges from neural activity?
Problems with this class of models • Neurons along the brain are similar. • If this is so, what is the difference between a neuron in the auditory cortex and one in the visual cortex? • Can we find the difference between these two neurons in descriptions like those above?
Computational Neuroscience(a more precise definition) • The ultimate aim of computational neuroscience is to explain how electrical and chemical signals are used in the brain to represent and process information. • Neurons and neuron circuits are best defined by their function. And their function is to represent and process information.
Cognitive Science and the Computational Theory of Mind (CTM) • PROBLEM: How desires, intentions, etc. can be the cause of behavior (how do pure mental phenomena cause behavior). • SOLUTION: (remember that dualism is untenable) • Analogy between the functioning of the mind and a computer program. • Mind is like software, brain is like hardware.
The CTM and Functionalism • Things are described by their function. • “..trying to understand perception by studying only neurons is like trying to understand flight by studying only feathers: It just cannot be done…”(Marr, 1982) Tema 7
Functionalism • We can design a mechanism made of iron, springs, pumps … that has the same function as a human heart and that can replace it. Hearts can be defined by their function. • We can imagine an alien completely different from us (without neurons, heart, ..) and who can do very complex reasoning. We can describe neurons or neural circuits by their function.
Cognitive Science • There are two key concepts: • Representations (information about the world or the inner state of the animal). • Computations (representations are computed and transformed in new representations). • We do not need neuroscience to understand intelligent behavior. Tema 7
The mind: a very complex computer • The mind is a system of organs of computation, designed by natural selection to solve the kinds of problems our ancestors faced in their foraging way of life, in particular, understanding and outmaneuvering objects, animals, plants, and other people. (Pinker 1997). • The mind is what the brain does; specifically, the brain processes information, and thinking is a kind of computation.
An example. Text to voice, the task of reading phonological representation /teik/ What are these neural circuits doing? Computing Orthografic representations TAKE Tema 7
HowdoesthebrainRepresentinformation? • Current representations: firing rate (number spikes/T). • Stored representations: synapses Tema 7
Testing the hypothesis“Single cell recording” • This technique has the highest resolution of all neuroimage techniques. • A thin electrode is inserted inside an animal's brain to record electrical changes of a single neuron. • We can count the spikes and then determine the firing rate of the neuron. Tema 7
Face representations (Desimone, 1991) Imagen reproducida de Desimone, R. (1991) Face-selective cells in the temporal cortex of monkeys, Journal of Cognitive Neuroscience, Vol 3(1), Tema 7
A B Desimone, R.(1991) Face-selective cells in the temporal cortex of monkeys, Journal of Cognitive Neuroscience, 3, (1). Tema 7
Testing the hypothesis Mirror - neurons • Definition: A mirror neuron is a neuron which fires both when performing an action and when observing the same action performed by another (possibly conspecific) creature. Tema 7
mirror-neurons Rizolatti, Fogassi and Gallese (2001) Neurophysiological mechanism underlying the understanding of imitation and action, Nature Reviews Neuroscience2, 661 - 670 Tema 7
Registro actividad neuronal del córtex premotor mientras el mono ve coger un objeto Idem, pero ahora el mono no ve cómo finaliza la acción pero “sabe” que hay un objeto Idem, pero ahora el mono no ve como finaliza el gesto pero “sabe” que no hay objeto Idem, mientras el mono ve el gesto pero ahora no hay objeto Tema 7
Mirrors • Seeing actions, emotions and feelings of other individuals may activate resonant mechanisms that allow the empathic understanding of others’ states. Being crucial for implementing pro-social behaviors, empathy is considered as inherently altruistic. • How? Tema 7
Mirror Neurons • They seem to explain the capacity of imitation and empathy of animals. • It is possible to explore whether the personal experience of pain make individuals less inclined to share others’ pain. • Perception of pain in others is self-centered (it depends of how we experience pain) Tornar Tema 7
Testing the hypothesis Microstimulatión • We can use electrodes to microstimulate neurons and cause modifications in their firing rates, usually increasing them. Tema 7
Visual cortex • We can imagine light impinging upon the eye and, from this origin point, a cascade of action potentials streaming from neuron to neuron, area to area, forwards, lateral and back again. In the abstract we know that it is these signals that are responsible for our vision of the external world. But how do these millions of patterned spikes resolve themselves into an actual percept?
Visual cortex • The brain breaks down every external image into components (e.g. lines, colors, textures, shades, and motion, etc.). • Neurons in the visual cortex are highly specialized to detect only one or a subset of these features (e.g. lines, colors, textures, shades, and motion, etc.).
Visual cortex Neurons in the visual cortex respond selectively to perceptually salient features of the visual scene, such as the direction and speed of moving objects, the orientation of local contours, or the colour or relative depth of a visual pattern
Testing orientation • The classic method for testing orientation and direction selectivity is to measure the spike rate of a single cell in response to drifting oriented luminance bars and/or drifting luminance spots .
Neuron specialization: orientation With this technique we can find in the V1 area neurons with a strong orientation and direction selectivities
Excersise • We can use microstimulatión to test the hypothesis on how the brain represents information. • How? • Have you seen “Matrix”?
Newsome experiment Nichols, M.J. & Newsome, W.T. (2002) Journal of Neuroscience, 22(21)9530:9540 Tema 7
100 % Coherencia • 0 % Coherencia • 5 % Coherencia Nichols, M.J. & Newsome, W.T. (2002) Journal of Neuroscience, 22(21)9530:9540 http://monkeybiz.stanford.edu/ Tema 7
Where the decisions take place motor cortex Visual cortex motor Tema 7
microestimulation Where the decisions take place Motor cortex Visual cortex Tornar Respuesta motora Tema 7
Inducing representations using microstimulation • Microstimulating the prelimbicsubregion excites fear behavior while the microstimulation of infralimbicsubregion inhibits fear behavior (Vidal-Gonzalez et al., 2006) • Phantom sensations generated by thalamic microstimulation (Davis et al, 2008) • Complex Movements Evoked by Microstimulation of Precentral Cortex (mardiz et al. 2006) Tema 7
Testing the hypothesis with FMRi ad the phenomenon of synesthesia http://www.fisicahoy.com/fisicaHoy/bioCerebro/bioCerebro.html Tema 7