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Connections between neurons are said (by Wikipedia) to be strengthened as part of learning - can they also be weakened (below the original level)?

I understand the concept of the connections strengthening. After reading the article Ants Swarm Like Brains Think, my understanding is that positive feedback (I forget the words that I should use for positive vs negative action potentials) should strengthen the connection, and negative feedback should weaken it.

I'm interested to know whether neural connections can weaken below their original connection strength.

I'm curious about this so as to grasp the way that the human brain (or even simply the ant brain) learns good and bad. If I'm not completely wrong about what I'm asking, then I think I get it pretty well: The things that are good (like finding food) trigger positive feedback among the associated neuron groups, and the things that are bad (like pain or danger) trigger negative feedback in the associated neurons, and that's basically how brains learn good from bad.

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Short answer
Yes, neural connections can be weakened.

Background
Chemical connections between neurons (synapses) can certainly be strengthened or weakened, dependent on their input. Single synapses can undergo long term potentiation (LTP) or long term depression (LTD). As a typical example there are hippocampal neurons. High-frequency (tetanic) electrical stimulation in hippocampal neurons can result in long-term potentiation (strengthening) of synaptic connections in the hippocampus Moreover, when a synapse receives synchronous input from multiple incoming axons they can potentiate each other's responses (Purves et al, 2001). In contrast, low-frequency stimulation and prolonged inactivity of synapses in the hippocampus can weaken them (Bear & Abraham, 1996).

The connection between learning, let alone good and bad as you ask for in your question, is far from clear. However, LTP and LTD do provide plausible mechanisms that could underpin these processes at the cellular level (Purves et al, 2001).

References
- Bear & Abraham, Ann Rev Neurosci (1996); 19: 437-62
- Purves et al., eds. Neuroscience, 2nd ed., Sunderland (MA): Sinauer Associates; 2001

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What you are talking about called synaptic plasticity, and sure it is possible to weaken connection between neurons, that's why for instance you can forget things.

In neuroscience, synaptic plasticity is the ability of synapses to strengthen or weaken over time, in response to increases or decreases in their activity.1 Plastic change also results from the alteration of the number of neurotransmitter receptors located on a synapse.2 There are several underlying mechanisms that cooperate to achieve synaptic plasticity, including changes in the quantity of neurotransmitters released into a synapse and changes in how effectively cells respond to those neurotransmitters.[3] Synaptic plasticity in both excitatory and inhibitory synapses has been found to be dependent upon postsynaptic calcium release.2 Since memories are postulated to be represented by vastly interconnected networks of synapses in the brain, synaptic plasticity is one of the important neurochemical foundations of learning and memory.

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neural connections can be weaken below their original connection strength. from neuroscience, new memories mean new neural connections, and the new neural connections require repeated activation. neurons that fire together, wire together, so it neurons or groups of neurons donot fire together often enough, new connections do not form.

i am not sure the relationship with ants, i think the neural connections is strength by frequently practice.

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  • $\begingroup$ So are you saying rather than the strength of individual connections increasing, more connections form which in turn makes the over-all connection between the two neurons stronger? $\endgroup$
    – J.Todd
    Commented Oct 15, 2014 at 18:36
  • $\begingroup$ yes. but i am not sure is there other thing or action can increase the strength of individual connection $\endgroup$
    – Viola philippica
    Commented Oct 15, 2014 at 18:48
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    $\begingroup$ It would be great if you provided some references for your response! $\endgroup$
    – Behzad Rowshanravan
    Commented Oct 15, 2014 at 19:00
  • $\begingroup$ I DO not remember where i found that, i only remember it is about Recursive Hierarchical Recognition (RHR) $\endgroup$
    – Viola philippica
    Commented Oct 15, 2014 at 19:16

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