|MadSci Network: Neuroscience|
"how many new neural connections would be made during an hour of watching tv (ID = 1046268059.Ns)" This is an interesting question - sorry it took so long to get back to you with an answer. The brain is quite interesting with its ability to form connections and communication with various other cells. Your question specifically is hard to answer since early in human development (say a newborn) the brain is not fully developed but as a teen or an adult most of the connections are well set into place. However, there is a recent surge in understanding of how neurons continue to be formed and added into adult brains. Lets first start with early development and watching TV. You probably heard of parents playing music to a mother's belly so that a fetus can "hear" the music. There is evidence that well developed fetuses can hear this sound. How this effects brain development is hard to determine, but that sound (noise) could also come from TV that pregnant mothers listens to and maybe the visual scenes that a pregnant mother watches might also have an indirect effect. So let say a pregnant mother is watching a horror movie on TV with bad scenes that scar her and she is very stressed out over the photos. Well that will trigger hormones to be released by the mother and those hormones will also be exposed to the developing fetus. It is known that hormones effect neural development and circuitry. So maybe these hormones released from a mother's TV watching will effect brain development. It is hard to know to what extent since it is to hard to make direct conclusions since so many other variables also have a role in brain development. I think your not interested in fetal development but I wanted to give you a full picture from the start. There is also strong evidence that in a new born and young babies the brains and the circuitry are not fully developed. Many environment cues from vision, sound, touch, taste, and smell effect how the brain will develop. Since your mostly interested to TV (vision and sound) lets just stick with vision since most of the current knowledge comes from earlier studies in vision. Sensory input at a baby or young child makes central circuits which can become relatively hard wired after defined critical periods. A critical period is a time in which the brain is still very plastic in forming circuits. After this time the brain (central nervous system) does not have as much plasticity (i.e., the ability it form new connections). This was most eloquently shown in the 1960's experimentally for the visual system in cats and monkeys (Hubel and Wiesel, 1963a,b, 1968, 1970) and is clinically relevant to man. This won Hubel and Wiesel a Noble Prize. Other parts of the brain also show similar dependences on sensory activity in development. The formation of cortical (the parts in the front of your brain) circuits is of interest since this controls thought processes and forms of learning (see a review by Pallas, 2001). Detailed experimentation of sensory systems defining the central nervous system (CNS) and motor nerves have been possible in relatively less complex organisms. An example is in the development of the asymmetric claws (a cutter and crusher claw) of lobsters (Lang et al. 1978) where Govind and his colleagues have demonstrated that juvenile lobsters depend on sensory stimulation for the asymmetry to occur (Govind and Pearce, 1986). When lobsters are not allowed to manipulate objects in their claws they will develop two cutter claws, where as if one claw is exercised a crusher claw will develop over subsequent molts for the side that had enhanced sensory stimulation. Not only is the muscle phenotype, biochemistry, and cuticle differentiated but the number of sensory neurons and the central nuropile in the thoracic ganglion is modified during development of the asymmetry (Govind et al, 1988; Govind and Pearce, 1985; Cooper and Govind, 1991). In my lab, we currently work in Drosophila (a fruit fly), to investigate sensory function in shaping central control of motor output. For proper function of synapses (the sites where one nerve cell communicates to another nerve cell), the communication is tightly regulated while at the same time remaining plastic enough to respond to changing circumstances and requirements. If synaptic transmission is too strong or weak, an inappropriate signal will be relayed. This kind of regulation is on going throughout an animals life (babies and adults) at the sites where motor nerves and muscle communication takes place. Studies of this phenomenon is well documented at the Drosophila neuromuscular junction during larval development (Li and Cooper 2001;Li et al., 2002). Genetic mutations in the Drosophila have been used to study regulation of development, plasticity, and maturation of synapses (Bennett and Pettigrew, 1975; Nudell and Grinnell, 1983; Wilkinson and Lunin, 1994; Wilkinson et al., 1992). Ok- so now I think there is a good understanding that in development of a baby watching TV, there would be many synapses being made from the visual cues. Maybe a baby or young child would get excited depending on what was showing. Think if a cute dog or cat was on and the baby or child started to jump up and down. That would help with making connections in the brain for muscle control. The child might lift its arm up and point at the TV- that would also add in sensory and motor connections to be made. On the other hand watching TV with nothing really showing, like some boring (for a kid or baby) talk show they might not get much stimulation out of it and thus not as many circuits would be active. Taking this to the next step related to your question, then probably not many synapses would be made. So how many synapses are made with an hour of TV ? Well , now you see that this question is hard to answer and if one considers the whole brain for learning, vision, hearing and muscle control it is very hard to understand how many synapses are used and being reinforced for developing circuits. For teens and adults maybe that 1 hour of TV watching, with something exciting on, has an effect on continued brain development but likely not as much as it would before the critical periods for young kids and babies, since after a critical period the brain is close to being "hard wired". But as I mentioned above, there is new evidence that new brain cells (neurons) are made in the adult brain from layers called the subventricular zone in our brains. These cells turn into neurons and migrate into the brain regions. This means that if the cells are to make new connections with other nerve cells that likely activity of these cells will have a large role in making the new connections remain active and stable. So maybe 1 hour of TV might help for connections with visual learning or trying to retain new information. This idea in adults of the new neurons joining into new circuits is very interesting and is currently one area of research that is very active in the neurosciences (See below 2 papers on this information obtained from the www from current papers on the subject): >> 1. The subventricular zone: new molecular and cellular developments. Conover JC, Allen RL. Cell Mol Life Sci 2002 Dec;59(12):2128-35 The Jackson Laboratory, 600 Main Street, Bar Harbor, Maine 04609, USA. email@example.com The subventricular zone (SVZ), which lines the lateral walls of the lateral ventricle, persists as a neurogenic zone into adulthood and functions as the largest site of neurogenesis in the adult brain. In recent years, with the acceptance of the concept of postembryonic mammalian neurogenesis, neurogenesis in the adult SVZ has been an area of active research. With the rapid accumulation of new information on the SVZ, some of which is contradictory, summarizing existing knowledge on the SVZ and outlining future research directions in this area become important. In this review, we will cover recent molecular and cellular investigations that characterize the SVZ niche, SVZ neurogenesis, and SVZ cell migration within the adult brain. 2. Current concepts in central nervous system regeneration. Gurgo RD, Bedi KS, Nurcombe V. Journal of Clinical Neuroscience 2002 Nov;9 (6):613-7 Department of Neurosurgery, Princess Alexandra Hospital, Brisbane, Australia A dictum long-held has stated that the adult mammalian brain and spinal cord are not capable of regeneration after injury. Recent discoveries have, however, challenged this dogma. In particular, a more complete understanding of developmental neurobiology has provided an insight into possible ways in which neuronal regeneration in the central nervous system may be encouraged. Knowledge of the role of neurotrophic factors has provided one set of strategies which may be useful in enhancing CNS regeneration. These factors can now even be delivered to injury sites by transplantation of genetically modified cells. Another strategy showing great promise is the discovery and isolation of neural stem cells from adult CNS tissue. It may become possible to grow such cells in the laboratory and use these to replace injured or dead neurons. The biological and cellular basis of neural injury is of special importance to neurosurgery, particularly as therapeutic options to treat a variety of CNS diseases becomes greater. >>> In short, to answer your question, it is very difficult to know how 1 hour of TV watching effects the number of synapses formed. It depends on so many factors (age, what type of show is on, the persons attention to the show). Also which parts of the brain are affected are hard to determine because maybe the person is not really paying attention, thus not learning, but just kind of sitting as a couch potato in a zoned out state of mind. Sorry for the long winded answers above but I wanted to make sure you understand why this is not a simple question and a simple answer can not be given. All the best, Robin L. Cooper References used above: Cooper RL, Govind CK (1991) Axon composition of the proprioceptive PD nerve during growth and regeneration of lobster claws. J Exp Zool 260:181- 193. Cooper RL, Neckameyer WS (1999) Dopaminergic neuromodulation of motor neuron activity and neuromuscular function in Drosophila melanogaster. Comp Biochem Physiol [B] 122:199-210. Cooper RL, Stewart BA, Wojtowicz JM, Wang S, Atwood HL (1995) Quantal measurement and analysis methods compared for crayfish and Drosophila neuromuscular junctions and rat hippocampus. J Neurosci Meth 61: 67-78. Govind CK, Pearce J (1985) Lateralization in number and size of sensory axons to the dimorphic chelipeds of crustaceans. J Neurobiol 16:111-125. Govind CK, Pearce J. (1986) Differential reflex activity determines claw and closer muscle asmmetry in developing lobsters. Science 233:354-356. Govind CK, Pearce J, Potter DJ (1988) Neural attrition following limb loss and regeneration in juvenile lobsters. J Neurobiol 19:667-680. Hubel DH, Wiesel TN (1963a) Receptive fields of cells in striate cortex of very young, visually inexperienced kittens. J Neurophysiol 26:994-1002. Hubel DH, Wiesel TN (1963b) Shape and arrangement of columns in cat striate cortex. J Physiol 165:559-568. Hubel DH, Wiesel TN (1968) Receptive fields and functional architecture of monkey striate cortex. J Physiol 195:215-243. Hubel DH, Wiesel TN (1970) The period of susceptibility to the physiological effects of unilateral eye closure in kittens. J Physiol 206:419-436. Lang F, Govind CK, Costello WJ (1978) Experimental transformation of muscle fiber properties in lobster. Science 201:1037-1039. Li H, Cooper RL (2001) Effects of the ecdysoneless mutant on synaptic efficacy and structure at the neuromuscular junction in Drosophila larvae during normal and prolonged development. Neurosci 106:193-200. Li H, Harrison D, Jones G, Jones D, Cooper RL (2001) Alterations in development, behavior, and physiology in Drosophila larva that have reduced ecdysone production. J Neurophysiol 85: 98-104. Li H, Peng X, Cooper RL (2002) Development of Drosophila larval neuromuscular junctions: Maintaining synaptic strength. Neurosci 115:505- 513. Nudell, B.M., and Grinnell , A.D. (1983) Regulation of synaptic position, size and strength in anuran skeletal muscle. J. Neurosci. 3: 161-176 Pallas SL (2001) Intrinsic and extrinsic factors that shape neocortical specification. Trends Neurosci 24:417-423. Wilkinson, R.S., and Lunin, S.D. (1994) Properties of "reconstructed" motor synapses of the garter snake. J. Neurosci. 14: 3319-3332. Wilkinson, R.S., Lunin, S.D., and Stevermer, J.J. (1992) Regulation of single quantal efficacy at the snake neuromuscular junction. J. Physiol. 448: 413-436.
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