MadSci Network: Neuroscience

Re: how many new neural connections would be made during an hour of watching tv

Date: Mon Mar 31 11:16:35 2003
Posted By: Robin Cooper, Faculty, neurobiology, Univ. of Kentucky
Area of science: Neuroscience
ID: 1046268059.Ns

"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.

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

Department of Neurosurgery, Princess Alexandra Hospital, Brisbane, 

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-

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 

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-

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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