There exits
a general agreement on the fact that
the mechanism of stimulus reinforcement learning which characterises
the responses of amygdala neuronal is probably located within the amygdala
itself, and they are based on i based on their physical characteristics of
the incoming signals [1, 3, 4, 5]
It is generally
accepted that, at least in primates,
the amygdala process the visual stimuli reaching it from
cortical areas in emotional terms. [4, 6,7 8].
LeDoux's [2,
5] has put into evidence the l, poorly coded, sensory inputs reaching directly
the amygdala for conditioned reinforcing The nature of the circuit
put into evidence by LeDoux implies the very simple nature of such stimuli (such as pure tones for the auditory
aspects). Rolls [4] underlies how a visual stimulus is normally analysed at
the object level before we can conceive a useful “representation
for input to a stimulus-reinforcement evaluation system such as the amygdala
or orbitofrontal cortex”…The point here is that emotions
are usually elicited to environmental stimuli analysed to the object level
(including other organisms), and not to retinal arrays of spots or pure tones
.
Rolls suggests the to elicit normally observed emotions,
human mind needs to process the information at the object level[4].
The amygdala reacts to a number of sensory stimulations as sound (LeDoux, ) and visual signals [4].
There are evidences of the tendency of the amygdala neurons
to oppose the reversing of learned responses [8] as opposite to other areas
of the brain involved in emotional states.
Some amygdala neurons that respond to rewarding visual stimuli also respond to relatively novel visual stimuli; this may implement the reward value which novel stimuli have[ 4]
It is quite clear from single neuron studies in non-human primates that some amygdala neurons are activated by a large class of rewarding and punishing stimuli [7, 8, 9, 10, 11].
Amygdala [12] projects its signals to the hypothalamus, the autonomic brainstem.
to the basal ganglia [13]. and to many areas of the temporal, orbitofrontal,
and insular cortices from which it receives inputs by backprojections.
[1] Damasio, A. 1994. Descartes' Error: Emotion, Reason, and the Human Brain. New York: Avon Press.
[2] LeDoux, J. 1996. The Emotional Brain. The Mysterious Underpinnings Of Emotional Life. New York: Simon and Schuster.
[3] Panksepp, J. 1998. Affective Neuroscience. Oxford: Oxford University Press.
[4] Rolls, E. T. (1999) The Brain and Emotion . Oxford University Press.
[5] LeDoux, J. E. (1994) Emotion, memory and the brain. Scientific American 270: 32-39.
[6] Leonard, C. M., Rolls, E. T., Wilson, F. A. W. and Baylis, G. C. (1985) Neurons in the amygdala of the monkey with responses selective for faces. Behavioural Brain Research 15: 159-176.
[7] Rolls, E. T. (1992a) Neurophysiological mechanisms underlying face processing within and beyond the temporal cortical visual areas. Philosophical Transactions of the Royal Society 335: 11-21.
[8] Rolls, E. T. (1992b) Neurophysiology and functions of the primate amygdala. In: The Amygdala , pp. 143-165, ed. J. P. Aggleton. Wiley-Liss.
[9] Ono, T. and Nishijo, H. (1992) Neurophysiological basis of the Kluver-Bucy syndrome: responses of monkey amygdaloid neurons to biologically significant objects. In: The Amygdala , pp. 167-190, ed. J. P. Aggleton. Wiley-Liss.
[10] Sanghera, M. K., Rolls, E. T. and Roper-Hall, A. (1979) Visual responses of neurons in the dorsolateral amygdala of the alert monkey. Experimental Neurology 63: 610-626.
[11] Wilson, F. A. W. and Rolls, E. T. (1993) The effects of stimulus novelty and familiarity on neuronal activity in the amygdala of monkeys performing recognition memory tasks. Experimental Brain Research 93: 367-382.
[12] Amaral, D. G., Price, J. L., Pitkanen, A. and Carmichael, S. T. (1992) Anatomical organization of the primate amygdaloid complex. In: The Amygdala , pp. 1-66, ed. J. P. Aggleton. Wiley-Liss.
[13] Everitt, B. and Robbins, T. W. (1992) Amygdala-ventral striatal interactions and reward-related processes. In: The Amygdala , pp. 401-430, ed. J. P. Aggleton. Wiley.
[14] Bush G., Luu P., Posner M. I., (2000), Cognitive and Emotional Influences in anterior cingulate cortex, Trends in Cognitive Sciences, 4, 6, pp. 215-222
[16] Morris JS, Frith CD, Perrett DI, Rowland D, Young AW, Calder AJ, Dolan RJ.A differential neural response in the human amygdala to fearful and happy facial expressions.Nature 1996 Oct 31;383(6603):812-5
[17]Paul J. Whalen, Scott L. Rauch, Nancy L. Etcoff, Sean C. McInerney, Michael B. Lee, and Michael A. Jenike Masked Presentations of Emotional Facial Expressions Modulate Amygdala Activity without Explicit Knowledge The Journal of Neuroscience, January 1, 1998, 18(1):411-418
[18] Ryuta Kawashima, Motoaki Sugiura, Takashi Kato, Akinori Nakamura, Kentaro Hatano, Kengo Ito, Hiroshi Fukuda, Shozo Kojima and Katsuki Nakamura The human amygdala plays an important role in gaze monitoring Brain, Vol. 122, No. 4, 779-783, April 1999
[19] Rolls, E. T. and Treves, A.
(1998) Neural Networks and Brain Function . Oxford University Press